ﺑﺎﺯﮔﺸﺖ ﺑﻪ ﺻﻔﺤﻪ ﻗﺒﻠﯽ
خرید پکیج
تعداد آیتم قابل مشاهده باقیمانده : -41 مورد

Sonographic findings associated with fetal aneuploidy

Sonographic findings associated with fetal aneuploidy
Author:
Bryann Bromley, MD
Section Editor:
Louise Wilkins-Haug, MD, PhD
Deputy Editor:
Vanessa A Barss, MD, FACOG
Literature review current through: Apr 2025. | This topic last updated: May 29, 2024.

INTRODUCTION — 

Aneuploidy is the most common genetic abnormality detected by prenatal diagnosis and refers to an abnormal number of chromosomes [1]. The aneuploidies most frequently detected prenatally involve chromosomes 21, 18, 13, and the sex chromosomes (eg, XXX, XXY, XYY, XO), which accounted for 53, 13, 5, and 12 percent of all chromosome abnormalities in the European Surveillance of Congenital Anomalies database of cases diagnosed prenatally and before one year of age [2]. These aneuploidies are more commonly identified in the first and second trimesters than in live born infants because of an increased risk of spontaneous loss of aneuploid fetuses over the course of pregnancy and termination of some affected pregnancies [3,4].

The antepartum detection of fetal aneuploidy is one of the pillars of prenatal screening programs, although it represents only a portion of the total genetic and structural risks that affect the fetus. Parental risk factors for genetic disease, results of cell-free DNA or biochemical marker screening, and/or sonographic findings associated with variably increased risks for aneuploidy are all considered in assessing the risk that the fetus is affected by a genetic condition. Diagnostic genetic testing (typically chorionic villus sampling or amniocentesis) is required to obtain a definitive genetic diagnosis. Fetal blood or tissue sampling may be required for some conditions. (See "Diagnostic amniocentesis" and "Chorionic villus sampling".)

Sonographic findings associated with fetal aneuploidy are discussed here. Implications of the sonographic findings other than aneuploidy, including extended genetic etiologies, and the comprehensive evaluation of the anomalous fetus are reviewed separately. Clinically significant genetic finding such as copy number variants may occur in low-risk patients, with low-risk cell free DNA screening results, and without sonographic findings (structural or markers) [5,6].

(See "Down syndrome: Overview of prenatal screening".)

(See "First-trimester combined test and integrated tests for screening for Down syndrome and trisomy 18".)

(See "Prenatal screening for common fetal aneuploidies: Cell-free DNA test".)

(See "Prenatal genetic evaluation of the fetus with anomalies or soft markers".)

(See "Enlarged nuchal translucency and cystic hygroma".)

(See "Fetal cerebral ventriculomegaly".)

FIRST TRIMESTER

Background — First-trimester measurement of nuchal translucency (NT) was the mainstay of screening for trisomy 21 between the mid-1990s and the early 2020s. Numerous studies reported that its use as a component of the "combined test" (maternal age, serum total or free beta human chorionic gonadotropin [beta-hCG], serum pregnancy-associated plasma protein A [PAPP-A], and a precise sonographic measurement of NT) detected 82 to 91 percent of cases of trisomy 21 in singleton pregnancies in the first trimester, with a fixed false-positive rate of 5 percent [7-9]. In 2011, cell-free DNA screening was introduced into clinical practice. It detects over 99 percent of fetuses with trisomy 21 and 98 to 99 percent of those with trisomies 18 and 13, with an overall screen-positive rate of 0.13 percent [10].

Offering all pregnant people prenatal genetic screening (with or without measurement of NT) and/or diagnostic testing is a standard part of prenatal care. The American College of Obstetricians and Gynecologists supports offering cell-free DNA screening to all pregnant individuals regardless of a priori risk [9]. Over the last decade, the expanded indications for the utilization of cell-free DNA screening and its superior screening performance has led to its broad utilization and concurrent decline in combined first-trimester screening using the NT measurement in the United States (and other countries) [11-13]. (See "First-trimester combined test and integrated tests for screening for Down syndrome and trisomy 18" and "Prenatal screening for common fetal aneuploidies: Cell-free DNA test".)

The identification of first-trimester ultrasound findings is of critical relevance as features such as enlarged (also called increased) NT, cystic hygroma, absent nasal bone, megacystis, first-trimester growth delay or structural anomalies, are additional factors for pregnant individuals to consider when deciding whether to pursue prenatal genetic screening, including the type of screening test, or whether to go directly to diagnostic testing [14,15].

Although medical societies appreciate and/or recommend the utilization of a baseline obstetrical ultrasound prior to cell-free DNA screening, there has been a decrease in utilization of first-trimester ultrasound in the setting of cell-free DNA screening for aneuploidy [16]. Forgoing the early anatomic fetal assessment between 11+0 and 13+6 weeks is not cost effective and delays diagnosis of many potentially detectable major and lethal malformations [17-21].

Nuchal translucency at 11+0 to 13+6 weeks

Diagnosis – Nuchal translucency (NT) is the clear space at the posterior fetal neck, between the spine and the skin edge (image 1). It is measured sonographically in the fetal midsagittal plane, most commonly when the crown-rump length (CRL) is 45 to 84 mm (approximately 11 to 14 weeks of gestation), but sometimes as early as CRL 38 mm (approximately 10+5 weeks of gestation).

An enlarged NT (image 2) is variably defined as measuring ≥3 or 3.5 mm or ≥95th or 99th percentile for gestational age by CRL.

Clinicians performing NT measurement as part of first-trimester combined risk assessment for common aneuploidies should be appropriately credentialed and quality performance monitored [22,23]. (See "First-trimester combined test and integrated tests for screening for Down syndrome and trisomy 18", section on 'Timing' and "Enlarged nuchal translucency and cystic hygroma", section on 'Prenatal diagnosis'.).

Significance – The risk of fetal genetic abnormalities and other adverse outcomes (eg, structural abnormalities, particularly congenital heart disease or fetal demise) increases as the NT becomes progressively larger [24-27]. If an enlarged NT is identified on ultrasound examination, genetic counseling should be provided to discuss its clinical significance (risk of genetic and structural abnormalities) and options for further evaluation [9].

A detailed first-trimester early anatomic ultrasound should be performed if resources are available and may impact the positive predictive value of an abnormal screening result [17,21,28-31]. Diagnostic genetic testing (via amniocentesis or chorionic villus sampling) and performance of a detailed ultrasound evaluation and fetal echocardiogram between 18 to 22 weeks of gestation to assess for structural abnormalities are recommended [32-34]. An intermediate early second-trimester obstetrical ultrasound evaluation can be considered as it will identify a significant number of structural anomalies [7].

If the patient declines diagnostic genetic testing, the option for screening with cell-free DNA can be considered, if not already performed. Although a precise measurement of NT is an important component of the combined test, in patients undergoing cell-free DNA screening for trisomy 21, 18, and 13, a precise measurement may not be required if the NT subjectively appears normal [17]. However, evaluation of the nuchal region and NT remain important, and if it subjectively appears enlarged, a precise measurement is useful to stratify risk for other genetic associations. An enlarged NT is associated with clinically relevant atypical chromosomal abnormalities (eg, deletion, duplication, unbalanced structural rearrangement, mosaicism, rare autosomal trisomy), submicroscopic aberrations, and single gene disorders (including RASopathies) [19,35-38]). If initial diagnostic genetic testing is normal, whole exome sequencing is an option but its role in this setting remains to be established [39].

Disappearance of an enlarged NT prior to 14 weeks gestation occurs in approximately 1 in 5 fetuses and is associated with an improved prognosis compared with those without regression. There is, however, a residual risk of aneuploidy (8 percent for NT >95th percentile [40]) and adverse outcome (17 percent for NT >95th percentile [40]).

More detailed information on pathogenesis, fetal evaluation, management, and prognosis are available separately. (See "Enlarged nuchal translucency and cystic hygroma", section on 'Enlarged nuchal translucency'.)

Early fetal lymphangiectasia (enlarged nuchal region/edema at 9 to 10 weeks)

Diagnosis – Early lymphangiectasia can be defined as NT >95th percentile for CRL 28 to 44 mm [41] or >2.2 mm [42] (image 3), or ≥2.5 mm [43,44], but data to establish these thresholds are limited.

Significance – In contrast to enlarged NT at 11+0 to 13+6 weeks, the significance of lymphangiectasia (early fetal edema) or thickened nuchal region at 9 to 10 weeks of gestation (CRL <45 mm) is not definitively established. It has been reported to be a marker for common autosomal trisomies, monosomy X, and other genetic and structural abnormalities [41-44]. Genetic counseling should be offered and detailed early anatomic imaging should be recommended, if resources are available [17,45]. (See 'Nuchal translucency at 11+0 to 13+6 weeks' above and 'Cystic hygroma' below.)

In a retrospective cohort study of 104 cases of early fetal edema, nuchal edema (>2.2 mm at CRL 28 to 44 mm) was present in 38.5 percent of cases and generalized edema was seen in 61.5 percent of cases [42]. An adverse pregnancy outcome (defined as a significant chromosomal abnormality, major structural defect, or miscarriage without genetic testing) occurred in 24 percent of cases. Overall, significant chromosomal anomalies were identified in 19.2 percent of cases (10 percent with nuchal edema and 25 percent with generalized edema).

In fetuses that reached the 11+0 to 13+6 week scan, the edema resolved (<3.5 mm) in 81.9 percent. Fetuses with NT <3.5 mm had fewer adverse outcomes than those with persistent NT ≥3.5 mm (10.9 versus 76.5 percent) [42].

In a study of 120 fetuses with a CRL <45 mm and NT ≥2.5 mm, 49.1 percent had a genetic abnormality and an additional 7.5 percent had a structural anomaly [43]. In this cohort, 32.5 percent of embryos ultimately were liveborn with no anomalies.

In a prospective study of 109 fetuses with CRL 25 to 44.9 mm and NT ≥2.5 mm, 35.8 percent had a composite adverse outcome [44]. Aneuploidy was detected in 22.9 percent, other genetic abnormalities in 6.4 percent, and structural anomalies without aneuploidy in 3.7 percent. Pregnancy loss occurred in 2.7 percent. In the subgroup of 41 patients with NT between 2.5 and 3.4 mm, 22 percent had adverse pregnancy outcome. Fetuses with persistently elevated NT on follow-up scan had a significantly higher risk of adverse outcome than those in whom the NT normalized (65.2 percent versus 14.3 percent). The authors recommended referring all patients with an NT ≥2.5 mm before 11 weeks to maternal-fetal medicine units.

Cystic hygroma

Diagnosis – A cystic hygroma is a singular or multi-loculated fluid collection, typically along the posterior fetal neck and back (image 4).

Significance – The cystic fluid collection is thought to represent abnormal lymphatic development with delayed communication between the lymphatic and vascular system. Communication may subsequently occur, resulting in reversal of this finding [46].

Cystic hygroma is associated with a substantially increased risk of autosomal trisomy (50 to 60 percent), copy number variants, as well as RASopathies (eg, Noonan syndrome) compared with fetuses without an enlarged NT [32,36,37,47]. Fetuses with a large septated cystic hygroma are at higher risk for monosomy X (Turner syndrome; 45,X). In euploid fetuses, 30 to 50 percent have structural anomalies, most commonly cardiac malformations [32,48].

If a cystic hygroma is identified on ultrasound examination, genetic counseling should be provided to discuss its clinical significance (risk of genetic and structural abnormalities) and options for further evaluation [9]. A detailed first-trimester early anatomic ultrasound should be performed if resources are available [17,21,28,29,49]. Diagnostic genetic testing (via amniocentesis or chorionic villus sampling) and performance of a detailed ultrasound evaluation and fetal echocardiogram at 18 to 22 weeks of gestation to assess for structural abnormalities are recommended. An early interim second-trimester obstetrical ultrasound evaluation can be considered as it will identify a significant number of structural anomalies [7]. If the patient declines diagnostic testing, the option for primary or secondary screening with cell-free DNA can be considered, if not already performed. More detailed information on pathogenesis, fetal evaluation, management, and prognosis are available separately. (See "Enlarged nuchal translucency and cystic hygroma", section on 'Cystic hygroma'.)

Jugular lymphatic sacs

Diagnosis – Fluid collections in the anterolateral aspect of the neck are thought to represent jugular lymphatic sacs (image 5). They are occasionally seen during the evaluation of NT and in the early second trimester.

Significance – The fluid collections are presumed to be due to delayed communication between the primitive lateral lymphatic cysts and the jugular lymphatic veins and are most commonly seen when NT is enlarged [50-52]. When associated with an enlarged NT, structural anomaly, or nuchal fold, there is a significant risk of genetic abnormality and adverse outcome [36]. Since jugular lymphatic sacs and enlarged NT are part of the same lymphatic process, they have not been added to screening paradigms and we don't really know if there is an increased contribution to risk above the NT or other findings. (See 'Nuchal translucency at 11+0 to 13+6 weeks' above and 'First-trimester structural anomalies' below and 'Thick nuchal fold' below and 'Second-trimester structural anomalies' below.)

If they are small and noted as an isolated finding in a patient with a normal NT, they tend to resolve and outcome is typically favorable [53,54].

First-trimester absent nasal bone

Diagnosis – When the fetal profile is viewed in the midsagittal plane, the nasal bone appears as an echogenic line within the bridge of the nose, under the skin edge. The nasal bone is considered present if this line is more echogenic than the overlying skin, and absent if it is not visualized, or less echogenic, than the overlying skin (image 6) [55].

Significance – In one review, the frequency of an absent nasal bone in euploid, trisomy 13, trisomy 18, and trisomy 21 fetuses was 2.5, 45, 53, and 60 percent, respectively [24]. In a euploid fetus, a nonvisualized nasal bone may reflect delayed maturation, rather than true absence of the nasal bone, and is reported in 4.7 percent of euploid fetuses with CRL 45 to 54 mm, progressively decreasing to 1 percent in those with a CRL of 74 to 84 mm.

Fetal karyotype has been suggested for fetuses with both absent nasal bone and NT between 95th and 99th percentile and microarray has been suggested for those with normal karyotype and both absent nasal bone and NT >99th centile [56].

Megacystis

Diagnosis – Megacystis (ie, an enlarged fetal bladder) is defined by longitudinal bladder length ≥7 mm at 10 to 14 weeks of gestation (image 7) [57,58].

Significance – Megacystis occurs in approximately 1 in 1500 pregnancies. It has been associated with chromosomal abnormalities, genetic syndromes, and anomalies of the urinary tract, but also may resolve spontaneously with good outcome [59].

In a retrospective cohort study of 98 patients with megacystis, the overall aneuploidy rate was 12 percent; trisomy 18 accounted for 50 percent of cases and trisomies 13 and 21 each accounted for 25 percent of cases [58]. The frequency of aneuploidy was unrelated to the magnitude of bladder distension in this and another study [60], but others have reported an association (approximately 24 percent frequency of aneuploidy at 7 to 15 mm and 11 percent frequency at >15 mm and these cases were associated with an increased risk for obstructive uropathy [57]).

In the subgroup of fetuses with isolated megacystis and NT measurement <95th percentile, no cases of aneuploidy were identified and 96 percent had resolution of the megacystis [58]. Of the 51 livebirths with resolution of the megacystis, 80 percent had normal outcome, 6 percent had vertebral defects, anal atresia, cardiac defects, tracheo-esophageal fistula, renal anomalies, and limb abnormalities (VACTERL) or imperforate anus/fistula, and 14 percent had other urologic diagnosis. In two patients with persistent megacystis, major urologic conditions were present. There were no cases of lower urinary tract obstruction among fetuses with a bladder length <12 mm.

First-trimester growth restriction

Diagnosis – If the gestational age has been established by history and an early ultrasound examination, then the diagnosis of growth delay is made when the CRL on a subsequent first-trimester ultrasound examination performed at least one to two weeks later indicates a gestational age that is >5 to 7 days younger than expected by the initial ultrasound examination. Additional information on diagnosis is available separately. (See "Diagnosis and outcome of first-trimester growth delay", section on 'Diagnosis'.)

Significance — Growth restriction associated with aneuploidy can occur as early as the first trimester. The severity of growth restriction correlates with the severity of the chromosomal abnormality.

In a study that compared the CRL of 144 aneuploid and 440 euploid fetuses between 9 and 13 weeks of gestation, a shorter than expected CRL (ie, observed/expected CRL ≤0.86) increased the risk of aneuploidy more than twofold (odds ratio [OR] 2.52) [61].

In other studies, the association between short CRL and aneuploidy was strong for trisomy 18 and 13 and triploidy, but not observed for trisomy 21 [61-63].

Additional information on the causes, evaluation, and outcome of first-trimester growth restriction is available separately. (See "Diagnosis and outcome of first-trimester growth delay", section on 'Possible etiologies' and "Diagnosis and outcome of first-trimester growth delay", section on 'Postdiagnostic evaluation' and "Diagnosis and outcome of first-trimester growth delay", section on 'Pregnancy outcome (singleton pregnancy)'.)

First-trimester structural anomalies

Diagnosis – The expanded use of ultrasound in the latter part of the first-trimester has led to the structured evaluation of fetal anatomic landmarks and subsequent early detection of fetal anomalies, and is cost effective [18]. In a systematic review, the overall detection rate for structural abnormalities among fetuses undergoing ultrasonography at 11 to 14 weeks was 51 percent (472 of 957) [64]. In a retrospective review of fetuses without known chromosomal abnormalities, the detection rate of anomalies was 27.6 percent in the first trimester [28]. In a similar study of twin gestations, the detection rate of anomalies was 27.1 percent for dichorionic twins and 52.6 percent for monochorionic twins (reflecting higher number of anomalies related to this type of twinning) [34].

Some anomalies, such as holoprosencephaly, abdominal wall defects, and major abnormalities of fetal contour, should be identifiable in most cases. Other abnormalities, including major cardiac malformations (movie 1) [65], facial clefts, and limb anomalies, are potentially identifiable, while still other anomalies, such as microcephaly or agenesis of the corpus callosum, are not seen in the first trimester due to their timing in development [28]. Use of a structured protocol including color Doppler imaging of the outflow tracts is important to maximize detection of fetal anomalies [17,21,29,45,49,65].

Significance – The finding of a fetal structural anomaly increases the possibility of a chromosomal abnormality or genetic defect. The frequency of a chromosomal abnormality depends on the specific anomaly, the number of anomalies, and the combination of anomalies identified. (See 'Second-trimester structural anomalies' below.)

The identification of a malformation should prompt consultation with a sonologist experienced in first-trimester anatomic imaging and genetic counseling, as well as consideration of diagnostic genetic testing.

Other — First-trimester Doppler markers for aneuploidy screening are not routinely assessed in the United States as they have a limited role given the widespread availability of cell-free DNA screening. Furthermore, the measurements are challenging to obtain, require additional credentialing, and Doppler has the potential to produce biologically significant temperature rises in the first-trimester fetus.

Although not typically of additional value in routine aneuploidy screening, the combination of the NT measurement, tricuspid valve, and ductus venosus flow patterns may be helpful in the early identification of congenital cardiac anomalies [66]. (See "Overview of ultrasound examination in obstetrics and gynecology", section on 'Safety'.)

Abnormal flow in the ductus venosus — Abnormal ductus venosus flow velocities have been observed in both aneuploid and euploid fetuses [67]. In one review, the frequency of reversed a-wave in the ductus venosus by karyotype was: euploid fetuses (3 percent), trisomy 13 (55 percent), trisomy 18 (58 percent), and trisomy 21 (66 percent) [24].

The incorporation of ductus venosus flow into the combined first-trimester risk assessment protocol has been reported to improve screening metrics for trisomy 21 [68,69]. An abnormal flow in the ductus venosus is also associated with major congenital cardiac anomalies, and utilization may enhance early detection [70,71].

Tricuspid regurgitation — Tricuspid regurgitation may be seen in both aneuploid and euploid fetuses. In one study, the frequency of tricuspid regurgitation at 11 to 13 weeks by karyotype was euploid fetuses (0.9 percent), trisomy 21 (55.7 percent), trisomy 18 (33.3 percent), trisomy 13 (30 percent), and monosomy X (37.5 percent) [72]. As an isolated finding, it is a poor screening tool for aneuploidy and congenital heart defects [73,74].

SECOND TRIMESTER

Background — Soft markers (described below) are sonographic findings that typically reflect normal variation in fetal anatomy but are associated with a small-to-moderate increased risk of aneuploidy. They may be transient, resolving with advancing gestational age or after birth, often with no clinical sequelae.

Historically, ultrasound findings were incorporated into a Bayes theorem to refine the patient's a priori risk for carrying a fetus with trisomy 21 based on maternal age or second-trimester screening results in what was termed a "genetic sonogram" [75-78]. At least one soft marker is identified by ultrasound in approximately 15 percent of second-trimester fetuses, with specific markers carrying different likelihood ratios with respect to trisomy 21 screening (table 1) [75-77,79]. The presence of multiple markers increases the likelihood of trisomy 21 [75-77,79], whereas the absence of markers has been associated with a 50 to 80 percent reduction in the maternal age-related risk, thus providing the parents with information that could be used to make informed choices on whether to pursue diagnostic genetic testing [75-78]. They should also understand the residual risk of genetic conditions in the setting of a low-risk cell-free DNA screen or combined first-trimester screen, including in the setting of a normal ultrasound examination [6].

Second-trimester soft markers include:

Echogenic intracardiac focus (EIF)

Choroid plexus cysts (CPCs)

Single umbilical artery (SUA)

Urinary tract dilation

Slightly shortened long bones (humerus, femur)

Hyperechoic bowel

Thickened nuchal fold

Absent or hypoplastic nasal bone

Because of the increased risk for fetal aneuploidy (table 1), the identification of a soft marker warrants a detailed sonographic evaluation of fetal anatomy to exclude the presence of additional markers, structural malformations, and growth restriction. The contemporary use of soft markers alone in screening for or excluding aneuploidy is inefficient compared with the first-trimester combined screening test and clinically negligibly contributive with respect to the major autosomal trisomies when cell-free DNA screening results are low risk. Even reporting the presence of some soft markers (EIF, CPCs) is controversial in a low-risk patient because this information is anxiety-provoking, requires considerable clinician time for counseling, and may lead to unwarranted diagnostic genetic testing.

The Society for Maternal-Fetal Medicine (SMFM) does not support diagnostic testing for aneuploidy in a patient solely for the indication of an isolated soft marker in the setting of a low-risk cell-free DNA screen [80,81]. This is because of the high specificity of cell-free DNA screening (near zero residual risk of trisomy 21) and the typically low or moderate increased risk conferred by the presence of an isolated marker (table 1) does not increase the risk estimate of aneuploidy sufficiently to warrant a recommendation for diagnostic testing [81]. However, in the setting of multiple soft markers, genetic counseling by a specialist provider is recommended as the residual risk depends on the specific marker and diagnostic genetic testing, including chromosomal microarray, may be reasonable [81,82]. Some soft markers, as described below, may have clinical implications other than aneuploidy; thus, amniocentesis may be recommended to evaluate for these other clinical conditions.

The genetic evaluation of the fetus with an isolated or multiple soft markers is reviewed separately. (See "Prenatal genetic evaluation of the fetus with anomalies or soft markers", section on 'Approach to the evaluation of the fetus with "soft markers" and no structural anomalies'.)

Soft markers

Echogenic intracardiac focus

Diagnosis – An echogenic intracardiac focus (EIF) is a punctate echogenic area that is typically seen in the left cardiac ventricle but may be seen in either or both ventricles. To be considered an EIF, it must be as bright as bone and seen in two imaging planes (image 8).

Significance – EIFs are not associated with myocardial dysfunction or structural cardiac anomalies [83]. An isolated EIF in the setting of an otherwise normal detailed structural survey (table 1) is considered a normal variant in the setting of a low-risk cell-free DNA screen.

The location and number of EIFs do not significantly affect the risk of aneuploidy. In the second trimester, 21 to 28 percent of fetuses with trisomy 21 have an EIF, compared with 3 to 5 percent of euploid fetuses [75]. The incidence varies across races (present in up to 30 percent of fetuses of Asian descent) and decreases with advancing gestational age [84,85]. It is thought to be related to microcalcification and fibrosis of the papillary muscle or chordae. In an autopsy study of abortuses, stillbirths, and perinatal deaths, discrete central papillary muscle calcification was more common in fetuses with trisomy 13 than trisomy 21 (39 and 16 percent, respectively, versus 2 percent of euploid controls) [86].

EIF is different from diffuse, extensive myocardial calcification, which is rare and associated with myocardial dysfunction [87].

For pregnant people with no previous aneuploidy screening and an isolated EIF, the SMFM recommends counseling to estimate the probability of trisomy 21 and a discussion of options for noninvasive aneuploidy screening with cell-free DNA, or quad screen if cell-free DNA is unavailable or cost-prohibitive [81]. For those with negative serum or cell-free DNA screening results and an isolated EIF, they recommend no further evaluation (ie, no indication for fetal echocardiography, follow-up ultrasound imaging, or postnatal evaluation).

Choroid plexus cysts

Diagnosis – Choroid plexus cysts (CPCs) are typically small (<10 mm in diameter) sonolucent structures with well-delineated borders within the choroid plexus of the cerebral lateral ventricles (image 9). They have a wide range of appearances, from unilateral single simple cysts to septated, bilateral, or multiple cysts.

Significance – Isolated CPCs in the setting of an otherwise normal detailed obstetrical ultrasound and low-risk aneuploidy screening are considered a normal variant [80]. They are not associated with adverse long-term developmental outcomes [88]. Those that persist beyond the second trimester are typically asymptomatic and benign.

CPCs are thought to result from filling of the neuroepithelial folds with cerebrospinal fluid [89]. The majority of studies suggest that a CPC that is isolated after a detailed anatomic survey (including examination of the face, heart, great vessels, and extremities including open hands) is highly reassuring of a normal karyotype [90,91]. In a meta-analysis, there were no cases of trisomy 18 among 1016 fetuses with isolated CPCs and maternal age less than 35 years [92].

Nonisolated CPCs increase the chances of aneuploidy. CPCs are present in 30 to 50 percent of fetuses with trisomy 18 compared with 0.6 to 3 percent of all second-trimester fetuses [93,94]; the frequency of CPCs is not increased in fetuses with trisomy 21 [95,96]. (See 'Trisomy 18 (Edward syndrome)' below.)

For pregnant people with no previous aneuploidy screening and isolated CPCs, the SMFM recommends counseling to estimate the probability of trisomy 18 and a discussion of options for noninvasive aneuploidy screening with cell-free DNA, or alternative aneuploidy screening if cell-free DNA is unavailable or cost-prohibitive [81]. For those with negative serum or cell-free DNA screening results and isolated CPCs, they recommend no further aneuploidy evaluation and no follow-up ultrasound imaging or postnatal evaluation.

Single umbilical artery

Diagnosis – Prenatal diagnosis of single umbilical artery (SUA) is based on ultrasound examination showing two instead of three vessels in the umbilical cord (cross section or longitudinally) (image 10). Color flow Doppler in the region of the bifurcation of the fetal aorta shows intra-abdominal umbilical vessels on only one side of the fetal bladder, which is pathognomonic of SUA (image 11). (See "Single umbilical artery", section on 'Prenatal diagnosis'.)

Significance – Aneuploidy is rare in a fetus with an isolated SUA after a detailed anatomic survey, and chromosomal analysis is not typically performed when no other malformations or indications for genetic amniocentesis are present [97]. However, when additional fetal malformations are detected, an association between SUA and risk of aneuploidy (trisomy 18) has been reported [98]. For fetuses with an isolated SUA, the SMFM recommends no additional evaluation for aneuploidy, regardless of whether previous results of aneuploidy screening were low risk or testing was declined [81].

Whether an isolated SUA is associated with other adverse outcomes such as fetal growth restriction (FGR) or stillbirth is unclear; however, given this possibility, a third-trimester scan for fetal growth is suggested and consideration of antenatal testing for fetal well-being [81]. Evaluation, management, and prognosis are discussed in more detail separately. (See "Single umbilical artery", section on 'Postdiagnostic evaluation' and "Single umbilical artery", section on 'Pregnancy management' and "Single umbilical artery", section on 'Pregnancy outcome'.)

Urinary tract dilation

Diagnosis – Mild (grade 1) antenatal (A) urinary tract dilation (UTD-A1; previously known as mild pyelectasis), is usually defined as a renal pelvic diameter of 4 to <7 mm pelvic dilation at 16 to 27 weeks of gestation (image 12 and figure 1). The maximal anterior-posterior dimension of the intrarenal pelvis should be measured with the fetal spine at 6 or 12 o'clock [99].

Significance – UTD-A1 is seen in 1 to 2 percent of fetuses overall, but 11 to 17 percent of fetuses with trisomy 21 (image 13) [75,99]. However, the presence of both a detailed anatomic survey and a low-risk cell-free DNA screen for fetal aneuploidy is reassuring. For pregnant people with no previous aneuploidy screening and isolated UTD-A1, the SMFM recommends counseling to estimate the probability of trisomy 21 and a discussion of options for noninvasive aneuploidy screening with cell-free DNA, or other screening options, if cell-free DNA is unavailable or cost-prohibitive; diagnostic genetic testing solely for the indication of UTD is not recommended in these cases [81]. For those with a negative serum or cell-free DNA screening results and UTD, they recommend no further aneuploidy evaluation. (See "Prenatal screening for common fetal aneuploidies: Cell-free DNA test".)

In most fetuses with UTD-A1, the finding is physiologic and transient, resolving over the course of gestation or in the postnatal period. Approximately 12 percent of fetuses with UTD-A1 have a postnatal urologic condition, and therefore follow-up imaging is recommended around 32 weeks gestation; if not resolved, postnatal follow-up is recommended [81,99]. For fetuses with more severe urinary tract dilation (antenatally categorized as UTD-A2 or 3), follow-up imaging and care should be individualized based on sonographic features and clinical circumstance. Prenatal and postnatal management are discussed in detail separately. (See "Fetal hydronephrosis: Etiology and prenatal management".)

Slightly short long bones

Diagnosis – Various criteria have been published for determining whether a femur or humerus is short with respect to aneuploidy screening [75,78]. The criteria are usually based on observed-to-expected ratios or multiple of the median with respect to biparietal diameter (BPD) [75,78]. We consider an observed-to-expected length ratio <0.9 to be abnormal (the expected length for gestational age is based on the 50th percentile for long bone length at the BPD-based gestational age) [75,78].

The femur must be measured meticulously with an angle of insonation perpendicular to the bone and the calipers at the end of the diaphysis. It is reported that as many as 13 percent of fetuses with a slightly short femur will have a normal femoral length on follow-up sonography within a short interval of time (false positive) [100].

Significance – The criteria for slightly short long bones overlap the range observed in unaffected fetuses and vary among different populations. A slightly short femur is detected in approximately 28 percent of fetuses with trisomy 21 and 6 percent euploid fetuses [75]. A shortened humerus is a slightly better predictor of trisomy 21 than a shortened femur (positive likelihood ratio 4.8 and 3.7, respectively) [75]. These two markers often occur in conjunction with each other [75,76].

For pregnant people with no previous aneuploidy screening and isolated shortened humerus, femur, or both, the SMFM recommends counseling to estimate the probability of trisomy 21 and a discussion of options for noninvasive aneuploidy screening with cell-free DNA, or other screening methods if cell-free DNA is unavailable or cost-prohibitive [81]. For those with negative serum or cell-free DNA screening results, they recommend no further aneuploidy evaluation but a third-trimester ultrasound examination for reassessment and evaluation of growth.

In contrast, a very short femur (<5th percentile) or abnormal appearing long bones may be a sign of a skeletal dysplasia, early onset FGR, and presence of pathogenic copy number variants [82,100-103]. Genetic counseling is strongly recommended to discuss residual risk of other genetic and structural anomalies. (See "Approach to prenatal diagnosis of life-limiting skeletal dysplasias".)

Echogenic bowel (hyperechoic bowel)

Diagnosis – Fetal hyperechoic bowel refers to increased echogenicity (brightness) of the fetal bowel noted on second-trimester sonographic examination (image 14A-B). To be considered hyperechoic, the bowel must be as bright as bone using a transabdominal transducer with a frequency of ≤5 MHz, with harmonics turned off and lower gain. This is important because higher frequency transducers and harmonics may result in the bowel appearing echogenic when it is not.

Significance – Hyperechoic bowel is seen in 13 to 21 percent of fetuses with trisomy 21 and 1 to 2 percent of euploid fetuses [75]. In fetuses with hyperechoic bowel, trisomy 21 is the most common aneuploidy identified. Isolated hyperechoic bowel has been reported with sex chromosome aneuploidies, which are potentially detectable with cell-free DNA screening [10]. (See "Prenatal screening for common fetal aneuploidies: Cell-free DNA test", section on 'Sex chromosome aneuploidies'.)

For pregnant people with no previous aneuploidy screening and isolated echogenic bowel, the SMFM recommends counseling to estimate the probability of trisomy 21 and a discussion of options for noninvasive aneuploidy screening with cell-free DNA, or quad screen if cell-free DNA is unavailable or cost-prohibitive [81]. For those with negative serum or cell-free DNA screening results, they recommend no further aneuploidy evaluation.

Hyperechoic bowel is transient, regressing or disappearing in up to 72 percent of fetuses [104], but it also can be associated with a variety of fetal and pregnancy complications, including cystic fibrosis, congenital infection, intraamniotic bleeding, FGR and gastrointestinal pathology. Clinical evaluation for these entities is discussed separately. (See "Fetal echogenic bowel".)

Because of the association with FGR, follow-up imaging in the third trimester is recommended to assess fetal growth. The appearance of an echogenic loop of large bowel in the late third trimester is normal and represents meconium. Early third-trimester appearance of echogenic bowel may be a harbinger of other genetic abnormalities, including cystinuria (image 15).

Thick nuchal fold

Diagnosis – The nuchal fold refers to the skin in the back of the fetal neck evaluated in the second trimester. The skin thickness is measured in an axial plane of the fetal head where the cavum septi pellucidum, thalami, cerebral peduncles, and the cerebellar hemispheres are demonstrated (image 16). The measurement is made from the outer edge occipital bone to the skin edge. A nuchal fold is considered thick if the measurement is ≥6 mm.

Significance – Increased thickness of the nuchal fold is one of the most sensitive markers for trisomy 21 in the second trimester, detected in at least 20 to 50 percent of fetuses with trisomy 21 and 0.5 to 2 percent of euploid fetuses. As an isolated finding, it carries a likelihood ratio for trisomy 21 of between 3 and 11 [75,76,79,105-108]. Although the thickened nuchal fold can revert to normal with advancing gestation, the risk of trisomy remains. (See 'Trisomy 21 (Down syndrome)' below.)

The SMFM recommends that pregnant people with no previous aneuploidy screening and isolated thickened nuchal fold receive counseling to estimate the probability of trisomy 21 and discuss options for noninvasive aneuploidy screening via cell-free DNA or quad screen if cell-free DNA is unavailable or cost-prohibitive, or diagnostic testing via amniocentesis, depending on clinical circumstances and patient preference [81]. For those with negative serum screening results and isolated thickened nuchal fold, they recommend counseling to estimate the probability of trisomy 21 and a discussion of options for no further aneuploidy evaluation, noninvasive aneuploidy screening via cell-free DNA, or diagnostic testing via amniocentesis, depending on clinical circumstances and patient preference. For those with low-risk cell-free DNA screening results and an isolated thickened nuchal fold or absent or hypoplastic nasal bone, they recommend no further aneuploidy evaluation.

A thick nuchal fold has also been observed with sex chromosome anomalies [109].

Second-trimester absent nasal bone

Diagnosis – Different methods have been proposed for determining a nasal bone to be short or hypoplastic; the most commonly utilized are a nasal bone length of ≤2.5 mm or a gestational age threshold of <2.5th or 5th percentile or <0.75 multiples of the median for gestational age (image 17) [110].

Significance – The reported sensitivity of absent nasal bone for trisomy 21 varies but is generally lower in the second than in the first trimester [111,112]. In the second trimester, the nasal bone is absent in approximately 30 to 40 percent of fetuses with trisomy 21 and 0.3 to 0.7 percent of euploid fetuses [75,113]. It is hypoplastic in approximately 50 to 60 percent of fetuses with trisomy 21 and 6 to 7 percent of euploid fetuses [113].

The finding of an isolated absent or hypoplastic nasal bone carries a likelihood ratio of 6.6 for trisomy 21 (table 1) [75]. For pregnant people with no previous aneuploidy screening and isolated absent or hypoplastic nasal bone, SMFM recommends counseling to estimate the probability of trisomy 21 and a discussion of options for noninvasive aneuploidy screening via cell-free DNA or quad screen if cell-free DNA is unavailable or cost-prohibitive, or diagnostic testing via amniocentesis, depending on clinical circumstances and patient preference [81]. For those with negative serum screening results and isolated absent or hypoplastic nasal bone, they recommend counseling to estimate the probability of trisomy 21 and a discussion of options for no further aneuploidy evaluation, noninvasive aneuploidy screening via cell-free DNA, or diagnostic testing via amniocentesis, depending on clinical circumstances and patient preference. For those with negative cell-free DNA screening results and isolated absent or hypoplastic nasal bone, they recommend no further aneuploidy evaluation.

Other markers

Mild to moderate ventriculomegaly

Diagnosis – Ventriculomegaly is identified on a transventricular view of the fetal head. The atria is measured at the level of the parieto-occipital sulcus with the calipers on the internal margin of the medial and lateral walls of the ventricle (image 18). Ventriculomegaly is diagnosed when the atrial diameter is ≥10 mm (irrespective of gestational age), which is 2.5 to 4 standard deviations above the mean, depending on the study. It is usually classified as mild: 10 to 12 mm; moderate: 13 to 15 mm; or severe: >15 mm (image 19).

Significance – The risk of an abnormal outcome in fetuses with mild ventriculomegaly depends on the cause (eg, trisomy 21, infection [eg, cytomegalovirus, toxoplasmosis], idiopathic) and increases with the degree of ventriculomegaly, progression over time, and presence of other anomalies. Mild to moderate ventriculomegaly is detected in 4 to 13 percent of fetuses with trisomy 21 and 0.1 to 0.4 percent of euploid fetuses [75].

The diagnosis, etiology, evaluation, pregnancy management, and prognosis of fetal ventriculomegaly are discussed in detail separately. (See 'Trisomy 21 (Down syndrome)' below and "Fetal cerebral ventriculomegaly".)

Second-trimester structural anomalies

Diagnosis – Sonographic examination is routinely performed at 18 to 22 weeks of gestation to evaluate the fetus for structural anomalies. (See "Overview of ultrasound examination in obstetrics and gynecology", section on 'Obstetric sonography'.)

Significance – As in the first trimester, the frequency of chromosomal abnormalities is increased in fetuses with sonographic evidence of structural anomalies. The magnitude of risk for a chromosomal abnormality is highly dependent upon both the specific malformation and the number of malformations. (See 'First-trimester structural anomalies' above.)

In retrospective series of prenatally detected anomalies on second- or third-trimester ultrasound that prompted genetic studies, an isolated fetal anomaly was associated with chromosome abnormalities in 2 to 18 percent of cases; multiple anomalies were associated with a fetal chromosome abnormality in 13 to 35 percent of cases [114-116]. By comparison, approximately 0.5 to 0.7 percent of all live born infants have a karyotypic abnormality [117,118]. Refer to individual topic reviews on specific congenital abnormalities for information on the risk of abnormal karyotype with each abnormality.

A low-risk result on cell-free DNA screening may be falsely reassuring in the setting of a structural anomaly and further diagnostic genetic testing (eg, genetic amniocentesis for microarray on amniocytes) may be indicated [119,120]. Even in the setting of a low-risk cell-free DNA screen and normal ultrasound, there is a residual risk of genetic abnormality [5,6]. (See "Prenatal genetic evaluation of the fetus with anomalies or soft markers".)

Second-trimester growth restriction

Diagnosis – Sonographic estimation of either fetal weight <10th percentile for gestational age or abdominal circumference <10th percentile for gestational age is the best finding on which to base the diagnosis of FGR. (See "Fetal growth restriction: Screening and diagnosis".)

Significance – Although the most common etiologies for small fetal size are uteroplacental insufficiency and constitutional factors, aneuploidy has been detected in 20 percent of pregnancies referred for further evaluation of a small fetus [121,122]. Most growth-restricted fetuses with chromosomal anomalies have associated findings, however, 2 to 6 percent of fetuses with isolated growth restriction have an abnormal karyotype [123]. Chromosomal microarray increases the detection of chromosomal abnormalities by 4 percent in nonanomalous fetuses and by 10 percent in those with structural abnormalities [124].

The incidence of growth restriction also varies with the type of aneuploidy. Among fetuses with trisomy 21, 13, and 18, growth restriction has been reported in 30, 50, and 90 percent of cases, respectively [125].

The SMFM suggests a detailed obstetrical ultrasound evaluation, genetic counseling, and offering diagnostic testing for patients with unexplained growth restriction before 32 weeks or anytime in gestation when noted in combination with a fetal malformation or polyhydramnios [122].

Other findings

Although more prevalent in fetuses with trisomy 21 than euploid fetuses, historical markers, such as a sandal gap, short ear length, and a hypoplastic wedge-shaped middle phalanx of the fifth digit that causes it to curve toward the fourth finger (clinodactyly), are common normal variants [126] and are not useful for aneuploidy screening.

An aberrant right subclavian artery is more common in fetuses with trisomy 21, being seen in 19 to 28 percent compared with 1 percent of euploid fetuses. In fetuses with trisomy 21, it is typically not an isolated finding [127,128]. It is also not usually associated with cardiac anomalies [129].

SONOGRAPHIC FEATURES OF SELECTED ANEUPLOIDIES

Trisomy 21 (Down syndrome) — Trisomy 21 is the most common aneuploidy to result in a live birth, occurring in 1 of 730 live births. (See "Down syndrome: Clinical features and diagnosis" and "Down syndrome: Routine health care, management of comorbidities, and prognosis".)

Approximately one-third of fetuses with trisomy 21 have one or more sonographically detectable structural malformations (major or minor) in the following systems [130]:

Cardiovascular, notably endocardial cushion defects and ventricular septal defects (40 to 50 percent)

Central nervous system (eg, mild ventriculomegaly)

Gastrointestinal system (eg, duodenal atresia [after 22 weeks] (image 20))

Craniofacial (eg, cystic hygroma, brachycephaly)

Hydrops fetalis (image 21)

Historically, identification of affected fetuses was achieved by utilizing Bayes theorem and genetic sonography (see 'Background' above) to modify a patient's a priori risk based on age and/or second-trimester maternal serum screening results. This approach is now obsolete, as it has been replaced by more sensitive and specific screening methods. The small-to-moderately increased risk of trisomy 21 conferred by the presence of an isolated soft marker is a negligible contributor to aneuploidy risk assessment after a low-risk cell-free DNA screen [81]. (See "Down syndrome: Overview of prenatal screening".)

Trisomy 18 (Edward syndrome) — Trisomy 18 is the second most common autosomal trisomy detected in the second trimester, occurring in 1 of 5000 live births. (See "Congenital cytogenetic abnormalities", section on 'Trisomy 18 syndrome'.)

Sonographic abnormalities include structural anomalies and markers (image 22):

Cardiovascular anomalies (complex congenital heart defects, ventriculoseptal defects, and valvular defects)

Central nervous system anomalies (neural tube defects, abnormal cisterna magna, agenesis of the corpus callosum, cerebellar anomalies, ventriculomegaly)

Facial anomalies (clefts, micrognathia, low-set ears, microphthalmia)

Gastrointestinal anomalies (omphalocele, diaphragmatic hernia)

Urogenital anomalies (horseshoe kidney, hydronephrosis)

Limb abnormalities (upper limb reduction [eg, radial ray defect]), clenched hands with overlapping index finger, clubbed feet, rocker bottom feet)

Nuchal fold thickening or cystic hygroma

Choroid plexus cyst(s) (CPC)

Strawberry shaped calvarium (pointed front and a flat occiput)

Single umbilical artery (SUA), umbilical cord cysts

Fetal growth restriction (FGR)

The frequency of sonographically detected anomalies in fetuses with trisomy 18 varies depending on gestational age, with anomalies detected in 76 percent of those less than 20 weeks and 93 percent at 20 weeks and beyond [131]. Some authorities have opined that by 19 to 20 weeks of gestation, genetic ultrasounds (detailed obstetrical ultrasounds) by experienced imagers should have 100 percent sensitivity (no false negatives) for detecting trisomy 18 [90,132]. (See "Prenatal screening for common fetal aneuploidies: Cell-free DNA test".)

In the third trimester, fetuses with trisomy 18 may have the unusual combination of polyhydramnios and FGR. In one series, 21 percent of trisomy 18 fetuses had FGR and polyhydramnios [133]. Trisomy 18 is especially likely when both findings are observed and associated with abnormal hand positioning.

Trisomy 13 (Patau syndrome) — Trisomy 13 occurs in 1 of 5000 live births, is the least common of the three major autosomal trisomies, and is associated with more severe and extensive structural malformations than trisomy 21 or 18. (See "Congenital cytogenetic abnormalities", section on 'Trisomy 13 syndrome'.)

Trisomy 13 is sonographically detectable in >95 percent of cases due to the presence of multiple major structural malformations of numerous organ systems, including [134-136]:

Central nervous system (alobar holoprosencephaly, neural tube defects, posterior fossa abnormalities, agenesis of the corpus callosum, ventriculomegaly)

Severe midline facial abnormalities (cyclopia, midline facial clefts, anophthalmia, hypoplastic nose)

Cardiac anomalies (complex congenital heart defects, ventriculoseptal defects)

Gastrointestinal anomalies (omphalocele, diaphragmatic hernia)

Renal anomalies (polycystic kidneys, enlarged echogenic kidneys, horseshoe kidneys)

Skeletal anomalies (postaxial polydactyly, club feet, rocker bottom feet)

Triploidy — Fetuses with triploidy have an extra haploid set of chromosomes (69). It affects 1 to 2 percent of conceptuses, with the majority resulting in first-trimester pregnancy loss. The prevalence decreases with advancing gestational age and is rare in live births. It is not associated with advancing maternal age.

Triploidy is associated with severe fetal anomalies and high mortality [137,138]. Fetal structural anomalies are seen in 84 percent of affected fetuses and are heterogeneous [137,138]:

Central nervous system anomalies (posterior fossa malformations, holoprosencephaly neural tube defects, ventriculomegaly)

Facial defects

Cardiac anomalies (complex congenital heart defects, tetralogy of Fallot, and transposition of great arteries)

Renal anomalies (agenesis and multicystic kidneys)

Syndactyly of the third and fourth digits, clenched hands

Clubbed feet

Absent gallbladder

Single umbilical artery (SUA)

Two phenotypic types are identifiable (image 23). When the extra set of chromosomes is maternal (digynic), FGR is associated with a normal size or large head, small trunk and limbs, a small placenta, and oligohydramnios. Abdominal circumference lagged behind head circumference by two weeks in one report of 21 cases between 12 and 16 weeks [139]. The nuchal translucency (NT) in fetuses with digynic triploidy is typically normal.

By comparison, when the extra set of chromosomes is paternal (diandric), FGR is symmetric and moderate and the placenta is usually large, cystic, and hydropic, suggesting a partial mole [139,140]. Fetuses with diandric triploidy may have a thickened NT. The additional paternal haploid complement is associated with maternal complications, including early onset hypertension, theca lutein cysts, hyperemesis gravidarum, and hyperthyroidism [138,141]. (See "Congenital cytogenetic abnormalities", section on 'Triploidy syndrome' and "Gestational trophoblastic disease: Pathology and genetics", section on 'Hydatidiform mole'.)

Monosomy X (Turner syndrome) — Monosomy X (45,X) occurs in 1 in 2000 live born females. In contrast to trisomy 21, 18, and 13, which occur as a result of nondisjunction and increase in incidence with increasing maternal age, monosomy X is caused by several different mechanisms and the incidence does not increase with increasing maternal age. Most conceptuses with monosomy X are spontaneously aborted in the first trimester. Those that survive pregnancy most often have either placental or fetal mosaicism of a 45,X and a euploid cell line.

Sonographic findings include [142,143]:

Large septate cystic hygroma (image 24)

Thickened nuchal fold

Hydrops fetalis, total body lymphangiectasia

Cardiac abnormalities (coarctation of aorta, ventriculoseptal defects, tetralogy of Fallot)

Short femur

Sixty percent of affected fetuses develop signs of hydrops [144]. Generalized hydrops associated with large septate cystic hygromata has a very poor prognosis, with only 1 percent surviving to infancy [145].

SUMMARY AND RECOMMENDATIONS

First trimester

Background – First-trimester measurement of nuchal translucency (NT) and assessment of serum analytes (total or free beta human chorionic gonadotropin [beta-hCG], pregnancy-associated plasma protein A) had been the mainstay of first-trimester screening for the three most common aneuploidies (trisomies 21, 18, and 13). Since 2011, use of cell-free DNA screening has been increasing because of its superior performance for these aneuploidies. As a result, precise measurements of nuchal translucency and identification of other sonographic markers associated with aneuploidy have decreased. Sonography is still important as aneuploidy represents only a portion of the total genetic and structural risks that may be identified in the fetus. (See 'Background' above.)

Sonographic findings associated with aneuploidy – First-trimester sonographic findings associated with, but not diagnostic of, major aneuploidies include NT ≥3 or 3.5 mm, cystic hygroma, absent nasal bone, megacystis, growth delay, and structural anomalies. (See 'Nuchal translucency at 11+0 to 13+6 weeks' above and 'Cystic hygroma' above and 'First-trimester absent nasal bone' above and 'Megacystis' above and 'First-trimester structural anomalies' above.)

Timing – First-trimester anatomic ultrasound screening is performed between 11+0 and 13+6 weeks and supports the optimal use of cell-free DNA screening. The use of a standardized imaging protocol will identify many major and lethal anatomic abnormalities. Utilization of color Doppler to assess the heart and great vessels improves the sensitivity of diagnosis for congenital cardiac abnormalities. If an anomaly is detected on screening, a detailed first-trimester anatomic assessment is recommended if resources are available.

When early anatomic imaging is not performed, many potentially detectable anomalies are not identified until the second trimester. Patients may lose the opportunity for timely retrieval of genetic information and access to multidisciplinary consultation. Patients who choose to terminate their pregnancies as part of their reproductive choice options may not be able to do so.

Approach to pregnancies with sonographic findings associated with aneuploidy – While offering all pregnant people fetal aneuploidy testing or diagnostic testing is part of routine care, the identification of an ultrasound finding is an additional factor that is important to consider when a patient assesses the options for genetic screening or diagnostic testing. (See 'Background' above.)

Second trimester

Risk of aneuploidy in fetuses with an isolated soft marker (echogenic intracardiac focus [EIF], choroid plexus cyst [CPC], single umbilical artery [SUA], urinary tract dilation [UTD], thickened nuchal fold, or absent/hypoplastic nasal bone) – The presence of one of these isolated soft markers alone is not an indication for diagnostic genetic testing for aneuploidy in patients with a low-risk cell-free DNA screen. (See 'Background' above.)

Risk of aneuploidy in fetuses with multiple soft markers – In the setting of multiple soft markers and a low-risk cell-free DNA screen, genetic counseling by a specialist provider is recommended as the residual risk will be dependent on the specific markers present. (See 'Background' above.)

Evaluation of fetuses with urinary tract dilation, echogenic (hyperechoic bowel), slightly short long bones (<5th percentile), and mild to moderate ventriculomegaly – Fetuses with any of these findings are at increased risk for adverse outcomes in addition to aneuploidy and thus have additional indications for diagnostic genetic testing (karyotype or microarray), other types of testing (eg, cystic fibrosis, infection), and structured follow-up. (See 'Urinary tract dilation' above and 'Echogenic bowel (hyperechoic bowel)' above and 'Slightly short long bones' above and 'Mild to moderate ventriculomegaly' above.)

Evaluation of fetuses with growth restriction – A detailed obstetrical ultrasound evaluation, genetic counseling, and the offer of diagnostic genetic testing for aneuploidy are indicated for patients with unexplained growth restriction before 32 weeks or anytime in gestation when noted in combination with a fetal malformation or polyhydramnios. (See 'Second-trimester growth restriction' above.)

Fetuses with sonographic evidence of a structural anomaly – These fetuses are at increased risk of having a genetic abnormality. The magnitude of risk is dependent upon the specific malformation and whether isolated or multiple structural anomalies are identified. A detailed ultrasound is recommended if not previously performed. The finding of a structural anomaly should prompt genetic counseling and a recommendation for diagnostic testing. Cell-free DNA screening is a less informative option for those declining diagnostic genetic testing. (See 'Second-trimester structural anomalies' above.)

ACKNOWLEDGMENT — 

The UpToDate editorial staff acknowledges Beryl R Benacerraf, MD, who contributed to earlier versions of this topic review.

  1. Toufaily MH, Westgate MN, Lin AE, Holmes LB. Causes of Congenital Malformations. Birth Defects Res 2018; 110:87.
  2. Wellesley D, Dolk H, Boyd PA, et al. Rare chromosome abnormalities, prevalence and prenatal diagnosis rates from population-based congenital anomaly registers in Europe. Eur J Hum Genet 2012; 20:521.
  3. Hook EB, Topol BB, Cross PK. The natural history of cytogenetically abnormal fetuses detected at midtrimester amniocentesis which are not terminated electively: new data and estimates of the excess and relative risk of late fetal death associated with 47,+21 and some other abnormal karyotypes. Am J Hum Genet 1989; 45:855.
  4. Loane M, Morris JK, Addor MC, et al. Twenty-year trends in the prevalence of Down syndrome and other trisomies in Europe: impact of maternal age and prenatal screening. Eur J Hum Genet 2013; 21:27.
  5. Maya I, Salzer Sheelo L, Brabbing-Goldstein D, et al. Clinical utility of expanded non-invasive prenatal screening compared with chromosomal microarray analysis in over 8000 pregnancies without major structural anomaly. Ultrasound Obstet Gynecol 2023; 61:698.
  6. Maya I, Salzer Sheelo L, Brabbing-Goldstein D, et al. Residual risk for clinically significant copy number variants in low-risk pregnancies, following exclusion of noninvasive prenatal screening-detectable findings. Am J Obstet Gynecol 2022; 226:562.e1.
  7. Le Lous M, Bouhanna P, Colmant C, et al. The performance of an intermediate 16th-week ultrasound scan for the follow-up of euploid fetuses with increased nuchal translucency. Prenat Diagn 2016; 36:148.
  8. Santorum M, Wright D, Syngelaki A, et al. Accuracy of first-trimester combined test in screening for trisomies 21, 18 and 13. Ultrasound Obstet Gynecol 2017; 49:714.
  9. American College of Obstetricians and Gynecologists’ Committee on Practice Bulletins—Obstetrics, Committee on Genetics, Society for Maternal-Fetal Medicine. Screening for Fetal Chromosomal Abnormalities: ACOG Practice Bulletin, Number 226. Obstet Gynecol 2020; 136:e48.
  10. Gil MM, Accurti V, Santacruz B, et al. Analysis of cell-free DNA in maternal blood in screening for aneuploidies: updated meta-analysis. Ultrasound Obstet Gynecol 2017; 50:302.
  11. Wen T, Thornburg LL, Norton ME, et al. Trends in Reporting of Nuchal Translucency Measurements After the Clinical Introduction of Cell-Free DNA Screening. Obstet Gynecol 2024; 143:811.
  12. Palomaki GE, Wyatt P, Rowsey R, et al. Numbers of prenatal cell-free DNA screens performed: Results of a 2022 CAP exercise. Prenat Diagn 2024; 44:946.
  13. van der Meij KRM, Sistermans EA, Macville MVE, et al. TRIDENT-2: National Implementation of Genome-wide Non-invasive Prenatal Testing as a First-Tier Screening Test in the Netherlands. Am J Hum Genet 2019; 105:1091.
  14. Vora NL, Robinson S, Hardisty EE, Stamilio DM. Utility of ultrasound examination at 10-14 weeks prior to cell-free DNA screening for fetal aneuploidy. Ultrasound Obstet Gynecol 2017; 49:465.
  15. Brown I, Fernando S, Menezes M, et al. The importance of ultrasound preceding cell-free DNA screening for fetal chromosomal abnormalities. Prenat Diagn 2020; 40:1439.
  16. Doulaveris G, Igel CM, Estrada Trejo F, et al. Impact of introducing cell-free DNA screening into clinical care on first trimester ultrasound. Prenat Diagn 2022; 42:254.
  17. AIUM Practice Parameter for the Performance of Detailed Diagnostic Obstetric Ultrasound Examinations Between 12 Weeks 0 Days and 13 Weeks 6 Days. J Ultrasound Med 2021; 40:E1.
  18. Battarbee AN, Vora NL, Hardisty EE, Stamilio DM. Cost-effectiveness of ultrasound before non-invasive prenatal screening for fetal aneuploidy. Ultrasound Obstet Gynecol 2023; 61:325.
  19. Bardi F, Beekhuis AM, Bakker MK, et al. Timing of diagnosis of fetal structural abnormalities after the introduction of universal cell-free DNA in the absence of first-trimester anatomical screening. Prenat Diagn 2022; 42:1242.
  20. Lugthart MA, Heinrich H, Ertugrul I, et al. Eliminating first trimester combined testing: Consequences for early detection of significant fetal anomalies. Prenat Diagn 2024; 44:544.
  21. International Society of Ultrasound in Obstetrics and Gynecology, Bilardo CM, Chaoui R, et al. ISUOG Practice Guidelines (updated): performance of 11-14-week ultrasound scan. Ultrasound Obstet Gynecol 2023; 61:127.
  22. Fetal Medicine Foundation: Certification: Nuchal translucency scan https://fetalmedicine.org/fmf-certification-2/nuchal-translucency-scan (Accessed on May 04, 2021).
  23. Thornburg LL, Bromley B, Dugoff L, et al. United States' experience in nuchal translucency measurement: variation according to provider characteristics in over five million ultrasound examinations. Ultrasound Obstet Gynecol 2021; 58:732.
  24. Nicolaides KH. Screening for fetal aneuploidies at 11 to 13 weeks. Prenat Diagn 2011; 31:7.
  25. Baer RJ, Norton ME, Shaw GM, et al. Risk of selected structural abnormalities in infants after increased nuchal translucency measurement. Am J Obstet Gynecol 2014; 211:675.e1.
  26. Jelliffe-Pawlowski LL, Norton ME, Shaw GM, et al. Risk of critical congenital heart defects by nuchal translucency norms. Am J Obstet Gynecol 2015; 212:518.e1.
  27. Bardi F, Bosschieter P, Verheij J, et al. Is there still a role for nuchal translucency measurement in the changing paradigm of first trimester screening? Prenat Diagn 2020; 40:197.
  28. Syngelaki A, Hammami A, Bower S, et al. Diagnosis of fetal non-chromosomal abnormalities on routine ultrasound examination at 11-13 weeks' gestation. Ultrasound Obstet Gynecol 2019; 54:468.
  29. Karim JN, Di Mascio D, Roberts N, et al. Detection of non-cardiac fetal abnormalities on ultrasound at 11-14 weeks: systematic review and meta-analysis. Ultrasound Obstet Gynecol 2024; 64:15.
  30. Dobson LJ, Reiff ES, Little SE, et al. Patient choice and clinical outcomes following positive noninvasive prenatal screening for aneuploidy with cell-free DNA (cfDNA). Prenat Diagn 2016; 36:456.
  31. Scott F, Smet ME, Elhindi J, et al. Late first-trimester ultrasound findings can alter management after high-risk NIPT result. Ultrasound Obstet Gynecol 2023; 62:497.
  32. Schreurs L, Lannoo L, De Catte L, et al. First trimester cystic hygroma colli: Retrospective analysis in a tertiary center. Eur J Obstet Gynecol Reprod Biol 2018; 231:60.
  33. AIUM Practice Parameter for the Performance of Fetal Echocardiography. J Ultrasound Med 2020; 39:E5.
  34. Buijtendijk MF, Bet BB, Leeflang MM, et al. Diagnostic accuracy of ultrasound screening for fetal structural abnormalities during the first and second trimester of pregnancy in low-risk and unselected populations. Cochrane Database Syst Rev 2024; 5:CD014715.
  35. Berger VK, Norton ME, Sparks TN, et al. The utility of nuchal translucency ultrasound in identifying rare chromosomal abnormalities not detectable by cell-free DNA screening. Prenat Diagn 2020; 40:185.
  36. Stuurman KE, Joosten M, van der Burgt I, et al. Prenatal ultrasound findings of rasopathies in a cohort of 424 fetuses: update on genetic testing in the NGS era. J Med Genet 2019; 56:654.
  37. Grande M, Jansen FA, Blumenfeld YJ, et al. Genomic microarray in fetuses with increased nuchal translucency and normal karyotype: a systematic review and meta-analysis. Ultrasound Obstet Gynecol 2015; 46:650.
  38. Sinajon P, Chitayat D, Roifman M, et al. Microarray and RASopathy-disorder testing in fetuses with increased nuchal translucency. Ultrasound Obstet Gynecol 2020; 55:383.
  39. Mellis R, Eberhardt RY, Hamilton SJ, et al. Fetal exome sequencing for isolated increased nuchal translucency: should we be doing it? BJOG 2022; 129:52.
  40. Müller MA, Pajkrt E, Bleker OP, et al. Disappearance of enlarged nuchal translucency before 14 weeks' gestation: relationship with chromosomal abnormalities and pregnancy outcome. Ultrasound Obstet Gynecol 2004; 24:169.
  41. Grande M, Solernou R, Ferrer L, et al. Is nuchal translucency a useful aneuploidy marker in fetuses with crown-rump length of 28-44 mm? Ultrasound Obstet Gynecol 2014; 43:520.
  42. Ramkrishna J, Menezes M, Humnabadkar K, et al. Outcomes following the detection of fetal edema in early pregnancy prior to non-invasive prenatal testing. Prenat Diagn 2021; 41:241.
  43. Lugthart MA, Bet BB, Elsman F, et al. Increased nuchal translucency before 11 weeks of gestation: Reason for referral? Prenat Diagn 2021; 41:1685.
  44. Bet BB, Lugthart MA, Linskens IH, et al. Adverse pregnancy outcome in fetuses with early increased nuchal translucency: prospective cohort study. Ultrasound Obstet Gynecol 2024; 64:164.
  45. Liao Y, Wen H, Ouyang S, et al. Routine first-trimester ultrasound screening using a standardized anatomical protocol. Am J Obstet Gynecol 2021; 224:396.e1.
  46. Malone FD, Ball RH, Nyberg DA, et al. First-trimester septated cystic hygroma: prevalence, natural history, and pediatric outcome. Obstet Gynecol 2005; 106:288.
  47. Scott A, Di Giosaffatte N, Pinna V, et al. When to test fetuses for RASopathies? Proposition from a systematic analysis of 352 multicenter cases and a postnatal cohort. Genet Med 2021; 23:1116.
  48. Scholl J, Durfee SM, Russell MA, et al. First-trimester cystic hygroma: relationship of nuchal translucency thickness and outcomes. Obstet Gynecol 2012; 120:551.
  49. Karim JN, Roberts NW, Salomon LJ, Papageorghiou AT. Systematic review of first-trimester ultrasound screening for detection of fetal structural anomalies and factors that affect screening performance. Ultrasound Obstet Gynecol 2017; 50:429.
  50. Bekker MN, Haak MC, Rekoert-Hollander M, et al. Increased nuchal translucency and distended jugular lymphatic sacs on first-trimester ultrasound. Ultrasound Obstet Gynecol 2005; 25:239.
  51. Sharony R, Tepper R, Fejgin M. Fetal lateral neck cysts: the significance of associated findings. Prenat Diagn 2005; 25:507.
  52. van Heesch PN, Struijk PC, Brandenburg H, et al. Jugular lymphatic sacs in the first trimester of pregnancy: the prevalence and the potential value in screening for chromosomal abnormalities. J Perinat Med 2008; 36:518.
  53. Meyberg-Solomayer G, Hamza A, Takacs Z, et al. The significance of anterolateral neck cysts in early diagnosis of fetal malformations. Prenat Diagn 2016; 36:332.
  54. de Mooij YM, Bekker MN, Spreeuwenberg MD, van Vugt JM. Jugular lymphatic sacs in first-trimester fetuses with normal nuchal translucency. Ultrasound Obstet Gynecol 2009; 33:394.
  55. Fetal Medicine Foundation. Nasal bone https://fetalmedicine.org/fmf-certification-2/nasal-bone (Accessed on May 04, 2021).
  56. Fantasia I, Stampalija T, Sirchia F, et al. First-trimester absent nasal bone: is it a predictive factor for pathogenic CNVs in the low-risk population? Prenat Diagn 2020; 40:1563.
  57. Liao AW, Sebire NJ, Geerts L, et al. Megacystis at 10-14 weeks of gestation: chromosomal defects and outcome according to bladder length. Ultrasound Obstet Gynecol 2003; 21:338.
  58. Kao C, Lauzon J, Brundler MA, et al. Perinatal outcome and prognostic factors of fetal megacystis diagnosed at 11-14 week's gestation. Prenat Diagn 2021; 41:308.
  59. Fontanella F, Duin L, Adama van Scheltema PN, et al. Fetal megacystis: prediction of spontaneous resolution and outcome. Ultrasound Obstet Gynecol 2017; 50:458.
  60. Lesieur E, Barrois M, Bourdon M, et al. Megacystis in the first trimester of pregnancy: Prognostic factors and perinatal outcomes. PLoS One 2021; 16:e0255890.
  61. Bahado-Singh RO, Lynch L, Deren O, et al. First-trimester growth restriction and fetal aneuploidy: the effect of type of aneuploidy and gestational age. Am J Obstet Gynecol 1997; 176:976.
  62. Sagi-Dain L, Peleg A, Sagi S. First-Trimester Crown-Rump Length and Risk of Chromosomal Aberrations-A Systematic Review and Meta-analysis. Obstet Gynecol Surv 2017; 72:603.
  63. Engelbrechtsen L, Brøndum-Nielsen K, Ekelund C, et al. Detection of triploidy at 11-14 weeks' gestation: a cohort study of 198 000 pregnant women. Ultrasound Obstet Gynecol 2013; 42:530.
  64. Rossi AC, Prefumo F. Accuracy of ultrasonography at 11-14 weeks of gestation for detection of fetal structural anomalies: a systematic review. Obstet Gynecol 2013; 122:1160.
  65. Karim JN, Bradburn E, Roberts N, et al. First-trimester ultrasound detection of fetal heart anomalies: systematic review and meta-analysis. Ultrasound Obstet Gynecol 2022; 59:11.
  66. Minnella GP, Crupano FM, Syngelaki A, et al. Diagnosis of major heart defects by routine first-trimester ultrasound examination: association with increased nuchal translucency, tricuspid regurgitation and abnormal flow in ductus venosus. Ultrasound Obstet Gynecol 2020; 55:637.
  67. Wiechec M, Nocun A, Matyszkiewicz A, et al. First trimester severe ductus venosus flow abnormalities in isolation or combination with other markers of aneuploidy and fetal anomalies. J Perinat Med 2016; 44:201.
  68. Timmerman E, Oude Rengerink K, Pajkrt E, et al. Ductus venosus pulsatility index measurement reduces the false-positive rate in first-trimester screening. Ultrasound Obstet Gynecol 2010; 36:661.
  69. Maiz N, Wright D, Ferreira AF, et al. A mixture model of ductus venosus pulsatility index in screening for aneuploidies at 11-13 weeks' gestation. Fetal Diagn Ther 2012; 31:221.
  70. Maiz N, Plasencia W, Dagklis T, et al. Ductus venosus Doppler in fetuses with cardiac defects and increased nuchal translucency thickness. Ultrasound Obstet Gynecol 2008; 31:256.
  71. Wagner P, Eberle K, Sonek J, et al. First-trimester ductus venosus velocity ratio as a marker of major cardiac defects. Ultrasound Obstet Gynecol 2019; 53:663.
  72. Kagan KO, Valencia C, Livanos P, et al. Tricuspid regurgitation in screening for trisomies 21, 18 and 13 and Turner syndrome at 11+0 to 13+6 weeks of gestation. Ultrasound Obstet Gynecol 2009; 33:18.
  73. Wiechec M, Nocun A, Wiercinska E, et al. First trimester tricuspid regurgitation and fetal abnormalities. J Perinat Med 2015; 43:597.
  74. Scala C, Morlando M, Familiari A, et al. Fetal Tricuspid Regurgitation in the First Trimester as a Screening Marker for Congenital Heart Defects: Systematic Review and Meta-Analysis. Fetal Diagn Ther 2017; 42:1.
  75. Agathokleous M, Chaveeva P, Poon LC, et al. Meta-analysis of second-trimester markers for trisomy 21. Ultrasound Obstet Gynecol 2013; 41:247.
  76. Bromley B, Lieberman E, Shipp TD, Benacerraf BR. The genetic sonogram: a method of risk assessment for Down syndrome in the second trimester. J Ultrasound Med 2002; 21:1087.
  77. DeVore GR. Second trimester ultrasonography may identify 77 to 97% of fetuses with trisomy 18. J Ultrasound Med 2000; 19:565.
  78. Benacerraf BR, Neuberg D, Bromley B, Frigoletto FD Jr. Sonographic scoring index for prenatal detection of chromosomal abnormalities. J Ultrasound Med 1992; 11:449.
  79. Aagaard-Tillery KM, Malone FD, Nyberg DA, et al. Role of second-trimester genetic sonography after Down syndrome screening. Obstet Gynecol 2009; 114:1189.
  80. Society for Maternal-Fetal Medicine (SMFM). Electronic address: [email protected], Norton ME, Biggio JR, et al. The role of ultrasound in women who undergo cell-free DNA screening. Am J Obstet Gynecol 2017; 216:B2.
  81. Society for Maternal-Fetal Medicine (SMFM). Electronic address: [email protected], Prabhu M, Kuller JA, Biggio JR. Society for Maternal-Fetal Medicine Consult Series #57: Evaluation and management of isolated soft ultrasound markers for aneuploidy in the second trimester: (Replaces Consults #10, Single umbilical artery, October 2010; #16, Isolated echogenic bowel diagnosed on second-trimester ultrasound, August 2011; #17, Evaluation and management of isolated renal pelviectasis on second-trimester ultrasound, December 2011; #25, Isolated fetal choroid plexus cysts, April 2013; #27, Isolated echogenic intracardiac focus, August 2013). Am J Obstet Gynecol 2021; 225:B2.
  82. Hu T, Tian T, Zhang Z, et al. Prenatal chromosomal microarray analysis in 2466 fetuses with ultrasonographic soft markers: a prospective cohort study. Am J Obstet Gynecol 2021; 224:516.e1.
  83. Wax JR, Donnelly J, Carpenter M, et al. Childhood cardiac function after prenatal diagnosis of intracardiac echogenic foci. J Ultrasound Med 2003; 22:783.
  84. Shipp TD, Bromley B, Lieberman E, Benacerraf BR. The frequency of the detection of fetal echogenic intracardiac foci with respect to maternal race. Ultrasound Obstet Gynecol 2000; 15:460.
  85. Achiron R, Lipitz S, Gabbay U, Yagel S. Prenatal ultrasonographic diagnosis of fetal heart echogenic foci: no correlation with Down syndrome. Obstet Gynecol 1997; 89:945.
  86. Roberts DJ, Genest D. Cardiac histologic pathology characteristic of trisomies 13 and 21. Hum Pathol 1992; 23:1130.
  87. Simchen MJ, Toi A, Silver M, et al. Fetal cardiac calcifications: report of four prenatally diagnosed cases and review of the literature. Ultrasound Obstet Gynecol 2006; 27:325.
  88. Singal K, Adamczyk K, Hurt L, et al. Isolated choroid plexus cysts and health and developmental outcomes in childhood and adolescence - A systematic review. Eur J Obstet Gynecol Reprod Biol 2023; 290:115.
  89. Shuangshoti, S, Netsky, M. Neuroepithelial (colloid) cysts of the nervous system. Further observations on pathogenesis, incidence, and histochemistry. Neurology 1966; 16:887.
  90. Yeo L, Guzman ER, Day-Salvatore D, et al. Prenatal detection of fetal trisomy 18 through abnormal sonographic features. J Ultrasound Med 2003; 22:581.
  91. Coco C, Jeanty P. Karyotyping of fetuses with isolated choroid plexus cysts is not justified in an unselected population. J Ultrasound Med 2004; 23:899.
  92. Demasio K, Canterino J, Ananth C, et al. Isolated choroid plexus cyst in low-risk women less than 35 years old. Am J Obstet Gynecol 2002; 187:1246.
  93. Benacerraf BR, Harlow B, Frigoletto FD Jr. Are choroid plexus cysts an indication for second-trimester amniocentesis? Am J Obstet Gynecol 1990; 162:1001.
  94. Hurt L, Wright M, Dunstan F, et al. Prevalence of defined ultrasound findings of unknown significance at the second trimester fetal anomaly scan and their association with adverse pregnancy outcomes: the Welsh study of mothers and babies population-based cohort. Prenat Diagn 2016; 36:40.
  95. Yoder PR, Sabbagha RE, Gross SJ, Zelop CM. The second-trimester fetus with isolated choroid plexus cysts: a meta-analysis of risk of trisomies 18 and 21. Obstet Gynecol 1999; 93:869.
  96. Bromley B, Lieberman R, Benacerraf BR. Choroid plexus cysts: not associated with Down syndrome. Ultrasound Obstet Gynecol 1996; 8:232.
  97. Friebe-Hoffmann U, Hiltmann A, Friedl TWP, et al. Prenatally Diagnosed Single Umbilical Artery (SUA) - Retrospective Analysis of 1169 Fetuses. Ultraschall Med 2019; 40:221.
  98. Jauniaux E, Ebbing C, Oyelese Y, et al. European association of perinatal medicine (EAPM) position statement: Screening, diagnosis and management of congenital anomalies of the umbilical cord. Eur J Obstet Gynecol Reprod Biol 2024; 298:61.
  99. Nguyen HT, Benson CB, Bromley B, et al. Multidisciplinary consensus on the classification of prenatal and postnatal urinary tract dilation (UTD classification system). J Pediatr Urol 2014; 10:982.
  100. Papageorghiou AT, Fratelli N, Leslie K, et al. Outcome of fetuses with antenatally diagnosed short femur. Ultrasound Obstet Gynecol 2008; 31:507.
  101. Weisz B, David AL, Chitty L, et al. Association of isolated short femur in the mid-trimester fetus with perinatal outcome. Ultrasound Obstet Gynecol 2008; 31:512.
  102. D'Ambrosio V, Vena F, Marchetti C, et al. Midtrimester isolated short femur and perinatal outcomes: A systematic review and meta-analysis. Acta Obstet Gynecol Scand 2019; 98:11.
  103. Kim U, Jung YM, Oh S, et al. Chromosomal Microarray Analysis in Fetuses With Ultrasonographic Soft Markers: A Meta-Analysis of the Current Evidence. J Korean Med Sci 2024; 39:e70.
  104. D'Amico A, Buca D, Rizzo G, et al. Outcome of fetal echogenic bowel: A systematic review and meta-analysis. Prenat Diagn 2021; 41:391.
  105. Benacerraf BR, Barss VA, Laboda LA. A sonographic sign for the detection in the second trimester of the fetus with Down's syndrome. Am J Obstet Gynecol 1985; 151:1078.
  106. Benacerraf BR, Frigoletto FD Jr, Cramer DW. Down syndrome: sonographic sign for diagnosis in the second-trimester fetus. Radiology 1987; 163:811.
  107. Benacerraf BR, Gelman R, Frigoletto FD Jr. Sonographic identification of second-trimester fetuses with Down's syndrome. N Engl J Med 1987; 317:1371.
  108. Nyberg DA, Souter VL. Sonographic markers of fetal trisomies: second trimester. J Ultrasound Med 2001; 20:655.
  109. Benacerraf BR, Laboda LA, Frigoletto FD. Thickened nuchal fold in fetuses not at risk for aneuploidy. Radiology 1992; 184:239.
  110. Sonek J. Nasal bone in screening for trisomy 21: defining hypoplasia. Am J Obstet Gynecol 2007; 197:335.
  111. Sonek JD, Cicero S, Neiger R, Nicolaides KH. Nasal bone assessment in prenatal screening for trisomy 21. Am J Obstet Gynecol 2006; 195:1219.
  112. Shanks A, Odibo A. Nasal bone in prenatal trisomy 21 screening. Obstet Gynecol Surv 2010; 65:46.
  113. Moreno-Cid M, Rubio-Lorente A, Rodríguez MJ, et al. Systematic review and meta-analysis of performance of second-trimester nasal bone assessment in detection of fetuses with Down syndrome. Ultrasound Obstet Gynecol 2014; 43:247.
  114. Staebler M, Donner C, Van Regemorter N, et al. Should determination of the karyotype be systematic for all malformations detected by obstetrical ultrasound? Prenat Diagn 2005; 25:567.
  115. Halliday J, Lumley J, Bankier A. Karyotype abnormalities in fetuses diagnosed as abnormal on ultrasound before 20 weeks' gestational age. Prenat Diagn 1994; 14:689.
  116. Rizzo N, Pittalis MC, Pilu G, et al. Distribution of abnormal karyotypes among malformed fetuses detected by ultrasound throughout gestation. Prenat Diagn 1996; 16:159.
  117. Hamerton JL, Canning N, Ray M, Smith S. A cytogenetic survey of 14,069 newborn infants. I. Incidence of chromosome abnormalities. Clin Genet 1975; 8:223.
  118. Maeda T, Ohno M, Matsunobu A, et al. A cytogenetic survey of 14,835 consecutive liveborns. Jinrui Idengaku Zasshi 1991; 36:117.
  119. Benachi A, Letourneau A, Kleinfinger P, et al. Cell-free DNA analysis in maternal plasma in cases of fetal abnormalities detected on ultrasound examination. Obstet Gynecol 2015; 125:1330.
  120. Reimers RM, Mason-Suares H, Little SE, et al. When ultrasound anomalies are present: An estimation of the frequency of chromosome abnormalities not detected by cell-free DNA aneuploidy screens. Prenat Diagn 2018; 38:250.
  121. Meler E, Sisterna S, Borrell A. Genetic syndromes associated with isolated fetal growth restriction. Prenat Diagn 2020; 40:432.
  122. Society for Maternal-Fetal Medicine (SMFM). Electronic address: [email protected], Martins JG, Biggio JR, Abuhamad A. Society for Maternal-Fetal Medicine Consult Series #52: Diagnosis and management of fetal growth restriction: (Replaces Clinical Guideline Number 3, April 2012). Am J Obstet Gynecol 2020; 223:B2.
  123. Sagi-Dain L, Peleg A, Sagi S. Risk for chromosomal aberrations in apparently isolated intrauterine growth restriction: A systematic review. Prenat Diagn 2017; 37:1061.
  124. Borrell A, Grande M, Pauta M, et al. Chromosomal Microarray Analysis in Fetuses with Growth Restriction and Normal Karyotype: A Systematic Review and Meta-Analysis. Fetal Diagn Ther 2018; 44:1.
  125. Tyson RW, Kalousek DK. Chromosomal abnormalities in stillbirth and neonatal death. In: Developmental Pathology of the Embryo, Dimmick JE, Kalousek DK (Eds), Lippincott, 1992.
  126. Hobbins JC, Lezotte DC, Persutte WH, et al. An 8-center study to evaluate the utility of mid-term genetic sonograms among high-risk pregnancies. J Ultrasound Med 2003; 22:33.
  127. De León-Luis J, Gámez F, Bravo C, et al. Second-trimester fetal aberrant right subclavian artery: original study, systematic review and meta-analysis of performance in detection of Down syndrome. Ultrasound Obstet Gynecol 2014; 44:147.
  128. Martínez-Payo C, Suanzes E, Nieto-Jiménez Y, et al. Is it useful to evaluate the presence of aberrant right subclavian artery in prenatal diagnosis ultrasounds? J Obstet Gynaecol Res 2021; 47:359.
  129. Paladini D, Sglavo G, Pastore G, et al. Aberrant right subclavian artery: incidence and correlation with other markers of Down syndrome in second-trimester fetuses. Ultrasound Obstet Gynecol 2012; 39:191.
  130. Papp C, Szigeti Z, Tóth-Pál E, et al. Ultrasonographic findings of fetal aneuploidies in the second trimester--our experiences. Fetal Diagn Ther 2008; 23:105.
  131. Becker DA, Tang Y, Jacobs AP, et al. Sensitivity of prenatal ultrasound for detection of trisomy 18. J Matern Fetal Neonatal Med 2019; 32:3716.
  132. Oyelese Y, Vintzileos AM. Is second-trimester genetic amniocentesis for trisomy 18 ever indicated in the presence of a normal genetic sonogram? Ultrasound Obstet Gynecol 2005; 26:691.
  133. Nyberg DA, Kramer D, Resta RG, et al. Prenatal sonographic findings of trisomy 18: review of 47 cases. J Ultrasound Med 1993; 12:103.
  134. Lehman CD, Nyberg DA, Winter TC 3rd, et al. Trisomy 13 syndrome: prenatal US findings in a review of 33 cases. Radiology 1995; 194:217.
  135. Watson WJ, Miller RC, Wax JR, et al. Sonographic detection of trisomy 13 in the first and second trimesters of pregnancy. J Ultrasound Med 2007; 26:1209.
  136. Benacerraf BR, Nadel A, Bromley B. Identification of second-trimester fetuses with autosomal trisomy by use of a sonographic scoring index. Radiology 1994; 193:135.
  137. Lugthart MA, Horenblas J, Kleinrouweler EC, et al. Prenatal sonographic features can accurately determine parental origin in triploid pregnancies. Prenat Diagn 2020; 40:705.
  138. Massalska D, Bijok J, Kucińska-Chahwan A, et al. Triploid pregnancy-Clinical implications. Clin Genet 2021; 100:368.
  139. Zalel Y, Shapiro I, Weissmann-Brenner A, et al. Prenatal sonographic features of triploidy at 12-16 weeks. Prenat Diagn 2016; 36:650.
  140. Joergensen MW, Niemann I, Rasmussen AA, et al. Triploid pregnancies: genetic and clinical features of 158 cases. Am J Obstet Gynecol 2014; 211:370.e1.
  141. Massalska D, Bijok J, Kucińska-Chahwan A, et al. Maternal complications in molecularly confirmed diandric and digynic triploid pregnancies: single institution experience and literature review. Arch Gynecol Obstet 2020; 301:1139.
  142. Bronshtein M, Zimmer EZ, Blazer S. A characteristic cluster of fetal sonographic markers that are predictive of fetal Turner syndrome in early pregnancy. Am J Obstet Gynecol 2003; 188:1016.
  143. Papp C, Beke A, Mezei G, et al. Prenatal diagnosis of Turner syndrome: report on 69 cases. J Ultrasound Med 2006; 25:711.
  144. Brumfield CG, Wenstrom KD, Davis RO, et al. Second-trimester cystic hygroma: prognosis of septated and nonseptated lesions. Obstet Gynecol 1996; 88:979.
  145. Levy AT, Berghella V, Al-Kouatly HB. Outcome of 45,X fetuses with cystic hygroma: A systematic review. Am J Med Genet A 2021; 185:26.
Topic 447 Version 45.0

References