Nuchal cord

INTRODUCTION — A loop of umbilical cord around the fetal neck (nuchal cord) is a common finding at delivery. In most cases, it is not associated with a significant increase in the rate of any clinically important adverse fetal/neonatal events. In case reports and small case series, tight nuchal cords have been associated with adverse outcomes, including fetal asphyxia, demise, and long-term neurodevelopmental consequences, but causality via constriction of the umbilical vessels often cannot be proven.

This topic will discuss issues related to prenatal diagnosis of nuchal cords, pregnancy and intrapartum management, and potential outcomes. Abnormalities of the umbilical cord are reviewed separately. (See "Umbilical cord abnormalities: Prenatal diagnosis and management".)

CLASSIFICATION — The term nuchal cord describes an umbilical cord that passes 360 degrees around the fetal neck. Nuchal cords can be classified as [1]:

●Single or multiple

●Loose or tight (ie, compressing the fetal neck)

●Type A or B (figure 1)

•Type A – The placental end crosses over the umbilical end, entangling the neck in an unlocked pattern

•Type B – The placental end crosses under the umbilical end, entangling the neck in a locked pattern

PATHOGENESIS — The occurrence of a nuchal cord(s) appears to be a random event, with increased risk among fetuses with excessive movement and/or a long umbilical cord [2,3]. In a retrospective study of singleton vaginal deliveries at term, an excessively long cord (≥70 cm in length) was far more common in pregnancies with a nuchal cord than in those with no nuchal cord (403/1451 [28 percent] versus 54/4733 [1 percent]) [4]. A case report described a fetus with an umbilical cord 150 cm in length and 10 loops around its neck [5].

INCIDENCE — The incidence of nuchal cords increases with increasing gestational age. At birth, the reported incidence ranges from 19 to 24 percent [6]. Cord entanglement of other fetal body parts (with the part completely encircled by cord) is less common, with one study reporting the following: limbs 4.2 percent, trunk 4.7 percent, multiple body parts 6.4 percent [7].

Single nuchal cords are more common than multiple nuchal cords. In a meta-analysis including over 270,000 births, the incidence of single, double, triple, and quadruple nuchal cords at delivery was reported to be 16, 3, 1, and <1 percent, respectively [6].

Maternal age, ethnicity, and parity do not appear to affect incidence [8].

PRENATAL DIAGNOSIS

Diagnosis — The prenatal diagnosis of a nuchal cord is based on an ultrasound examination documenting that at least 75 percent of the neck is encircled by umbilical cord. This is a pragmatic approach because, near term and depending on the lie of the fetus, imaging 100 percent of the neck is not always possible. Color Doppler imaging or Doppler flow velocimetry helps to confirm a diagnosis made by gray-scale imaging. (See 'Diagnostic evaluation and performance of ultrasound' below.)

Although ultrasound cannot consistently and reliably distinguish between tight and loose nuchal cords [9,10], circular indentation of the fetal neck ("divot sign") suggests that the cord is tight [11,12]. Tightness can change during labor as the fetus descends through the birth canal.

Diagnostic evaluation and performance of ultrasound — Both longitudinal and transverse views of the fetal neck should be obtained (image 1). The presence or absence of a nuchal cord can be determined by color Doppler (image 2), even in the first trimester (movie 1 and movie 2).

The sensitivity of ultrasound for diagnosis of a nuchal cord at term has generally been reported to be approximately 70 percent for gray-scale imaging [9,13], increasing to 83 to 97 percent with color Doppler [9,13-15], which should be performed.

In a study that compared the diagnostic performance of two-dimensional, color Doppler, and three-dimensional (3D) ultrasound for predicting a nuchal cord at birth in 120 singleton pregnancies, the overall performance of these techniques was [13]:

●Gray-scale – Sensitivity 68.6 percent, specificity 80 percent, accuracy 76.7 percent

●Color Doppler – Sensitivity 82.9 percent, specificity 77.7 percent, accuracy 79.2 percent

●3D ultrasound – Sensitivity 71.4 percent, specificity 82.4 percent, accuracy 79.2 percent

These differences were not significant, possibly due to the small number of pregnancies with a nuchal cord (n = 35) and the high proportion with multiple nuchal cords (5/35).

Nuchal cords are easier to detect when there are multiple loops and with 3D ultrasonography [10,14]. Ultrasound correctly identifies 72 percent of single and 94 percent of multiple nuchal cords, with greatest sensitivity after 36 weeks (93 versus 67 percent) [16].

Differential diagnosis — Sonographic findings that may be misdiagnosed as a nuchal cord include a cord adjacent to but not encircling the fetal neck, posterior cystic neck mass, fetal skin folds, and amniotic fluid pockets [17]. Obtaining multiple real-time images from different angles and Doppler imaging can readily distinguish a nuchal cord encircling the fetal neck from these other entities.

SCREENING — We do not screen for the presence of a nuchal cord, given the lack of high-or even moderate-quality evidence that prenatal diagnosis of nuchal cords improves pregnancy outcome (see 'Possible sequelae' below). The American Institute of Ultrasound in Medicine does not consider attempts to visualize a nuchal cord a part of the standard prenatal ultrasound examination [18], and prenatally diagnosed nuchal cords are not routinely reported in ultrasound reports since they can be considered a normal finding. However, others have suggested that screening for complex umbilical cord entanglements (eg, >3 loops of nuchal cords, any combination of nuchal cord with a true knot, presence of a single umbilical artery) and prudent follow-up may be of benefit [19].

The potential harms of screening are that it may cause maternal anxiety and lead to unnecessary sonographic follow-up appointments, antepartum fetal assessment, and intervention in the absence of evidence that the nuchal cord significantly increases the risk of an adverse fetal outcome [20].

For patients who ask about a nuchal cord during their ultrasound examination, we reassure them that visualization of nuchal cord is a common incidental finding, often resolves, has not been associated with a markedly increased risk of adverse pregnancy outcome, and does not warrant specific changes in prenatal or intrapartum care based on this finding alone. (See 'Pregnancy management' below.)

NATURAL HISTORY — A nuchal cord may persist or resolve, and those that resolve may reform [3,21]. Although formation and resolution appear to be random events, persistence may be more likely at term and with multiple nuchal cords. The type of nuchal cord impacts the course; a type A nuchal cord can become undone with fetal movement, whereas a type B nuchal cord cannot undo itself and can form a true knot when it passes caudally over the fetal body (figure 1).

POSSIBLE SEQUELAE — In general, studies describing possible sequelae of nuchal cords are of low to moderate quality due to factors such as publication bias, lack of comparison with an adequate control group, limitations of reporting (eg, number of loops, tightness [which can change during labor], and type [A versus B]), and, in some cases, small numbers of subjects and events.

Fetal or neonatal demise — Risk of stillbirth in fetuses with nuchal cords may depend on the number of loops present, with multiple loops (and not single loops) increasing the risk of stillbirth; however, this finding may not be an independent risk factor. In the meta-analysis of 145 studies including over 270,000 births discussed above (see 'Incidence' above), the risk of stillbirth was twofold higher in pregnancies with multiple (≥2) cords compared with single or no cords (odds ratio [OR] 2.36, 95% CI 0.99-5.62); however, this was not statistically significant [6]. The rate of stillbirth was similar when comparing single versus no nuchal cord.

Risk of stillbirth is also increased when a true knot is present. In this meta-analysis, the risk was fourfold higher in pregnancies with a true cord knot (OR 4.65, 95% CI 2.09-10.37) [6]. Furthermore, the presence of a single umbilical artery in combination with cord entanglement may be an additional risk factor as return of unoxygenated fetal blood to the placenta might be impaired due to the lack of decompression by the second artery [19]. However, it is important to note that the presence of multiple nuchal cords (or true knot) is alone insufficient evidence of demise due to strangulation; causality can be supported by the presence of the following findings:

●Petechial hemorrhages, particularly of the face and subconjunctival area, and the neck, which are characteristic findings in strangulation [22,23].

●Vascular congestion and thrombosis of umbilical cord vessels [22,23].

●Cord edema or hemorrhage into the Wharton jelly [22,23].

●Vascular ectasia, vascular thrombosis, and/or thrombotic vasculopathy (avascular villi, villous stromal karyorrhexis) involving the umbilical cord vessels and/or chorionic plate and stem villous vessels [24,25].

●Absence of other conditions associated with fetal demise.

One potential mechanism for fetal asphyxia is restriction of carotid artery blood flow from tight entanglement around the neck; however, jugular venous compression may be sufficient to cause asphyxia and demise. Another potential mechanism is compression of the umbilical cord vessels themselves, especially the thin walled umbilical vein, when the cord becomes tightly compressed against itself or the fetal neck. Multiple mechanisms may be involved.

Of note, a tight nuchal cord that impeded fetal oxygenation before delivery may not be tight at delivery because loss of fetal tone with increasing cerebral hypoxia may lead to loosening of the nuchal cord if multiple loops are not present.

Impaired intrauterine growth — The effect of nuchal cords on fetal growth is less clear. In the meta-analysis discussed above (see 'Incidence' above and 'Fetal or neonatal demise' above), nuchal cord was not associated with birth weight <2500 grams (OR 0.66, 95% CI 0.5-1.35), but there was a trend toward fetal growth restriction and small for gestational age infants (OR 1.41, 95% CI 0.9-2.21) [6]. Limitations of this analysis include that the effect of single versus multiple nuchal cords on birth weight was not reported separately and the quality of evidence was low to moderate.

Abnormalities in tests for fetal evaluation

First-trimester combined test for Down syndrome screening — A nuchal cord may be detected incidentally during measurement of nuchal translucency and may alter the nuchal translucency (NT) measurement if it is tight, or it may not be detected and incorrectly included in the measurement [26,27]. In one prospective study including 53 fetuses with a nuchal cord during NT measurement (incidence 4.65 percent), the largest NT measurement overestimated NT in 50 percent, underestimated NT in 2 percent, and estimated NT correctly in 48 percent of cases compared with the true NT measurement after resolution of the nuchal cord [26].

If a nuchal cord is indenting the fetal neck, we suggest obtaining a NT measurement after resolution, which typically occurs within a short period of time. The median time to resolution was 2.21 hours in the study described above [26]. If the cord is loose, NT can be measured accurately as long as correct anatomic landmarks are used. If the nuchal cord does not resolve, measurements of NT above and below the cord will be different; the average of the two measurements is used to calculate risk [28].

Nonstress test, biophysical profile, Doppler indices — Information on the effect of nuchal cords on the nonstress test is sparse. Theoretically, vigorous fetal movement can tighten the nuchal cord, resulting in compression of carotid and umbilical blood vessels. The potential fetal heart rate consequences are variable decelerations and possibly late decelerations [2,29-31]. However, at least one small retrospective study of variable decelerations during reactive nonstress tests found no correlation with the frequency of nuchal cords or other cord entanglements [32]. (See "Intrapartum fetal heart rate monitoring: Overview", section on 'Physiologic significance of selected FHR characteristics'.)

Prospective studies have reported similar Doppler indices in the cerebral arteries of fetuses with and without nuchal cords [14,33,34]. Other prospective studies of term and postterm pregnancies have not reported a reduction in prelabor amniotic fluid levels in pregnancies with nuchal cords [10,35,36].

These findings in large series do not exclude the possibility that an individual fetus with a tight nuchal cord may become compromised. As an example, a case report described absent fetal movement on a routine ultrasound examination of a 30-week appropriate for gestational age fetus [12]. Doppler velocimetry revealed absent end-diastolic Doppler flow and cardiotocography showed repetitive severe variable decelerations. Emergency cesarean birth was performed with delivery of a 1200 gram, acidemic (pH 7.10) newborn with a tight double nuchal cord. Laboratory evaluation and placental histopathology were otherwise normal so the metabolic acidosis was attributed to the nuchal cords.

Intrapartum fetal heart rate — Small prospective studies of newborn outcomes after antenatal identification of nuchal cords have generally not described increased rates of nonreassuring fetal heart rate patterns or operative delivery [10,35-37]. By contrast, three large retrospective studies reported increases in the frequency of abnormal fetal heart rate tracings in pregnancies with nuchal cords compared with no nuchal cord [38-40]. While the overall cesarean delivery rate was not increased [38,39], an increase in emergency cesarean birth was noted in one study [39]. Both studies observed a higher rate of labor induction in pregnancies with a nuchal cord, which may account, at least in part, for the increased frequency of fetal heart rate abnormalities. Multiple nuchal cords appear to increase the risk of an abnormal fetal heart rate tracing [41-43].

A study that used near-infrared spectroscopy to assess the intrapartum effect of nuchal cords on cerebral hemodynamics and oxygenation found that nuchal cords were associated with an increase in cerebral blood volume during contractions, without a significant effect on cerebral oxygenation or neonatal outcome [37]. An increase in variable decelerations was also noted. The authors hypothesized that these findings were due to transient compression of the jugular veins by the cord during contractions.

Short-term newborn issues — Short-term outcomes of live born neonates with a tight nuchal cord are generally favorable. In the largest available dataset, in which a tight nuchal cord (defined as inability to manually reduce the loop over the head) was documented in 6.6 percent of 219,337 live births, there was no statistical association with adverse neonatal outcome (eg, admission to a neonatal intensive care unit, administration of dopamine, blood transfusion, death) [44]. Similarly, there were no differences in outcomes between the subset of very low birth weight neonates with a tight nuchal cord compared with those with no nuchal cord, although a small increase in one or more adverse outcomes could not be excluded conclusively. In small studies and case series, neonatal hypovolemia, hypotension, decreased perfusion and mild respiratory distress have been associated with a tight nuchal cord [16].

Long-term risks in children — There is no strong evidence that a nuchal cord increases the risk of neurodevelopmental impairment among live borns, but few long-term outcome data are available. One study compared neurodevelopmental performance at one year of age for 66 infants with nuchal cords at birth and 124 infants without a nuchal cord [45]. Although the development scores of both groups were in the normal range and averaged well above the standard means, the nuchal cord group had slightly, but statistically, lower scores, which was attributed to the cases with multiple or tight nuchal cords with intrapartum signs of fetal compromise.

It is not clear whether a nuchal cord increases the risk for developing cerebral palsy [46-50]. In a large retrospective cohort study including more than 240,000 singleton deliveries followed until the age of 18, the risk of cerebral palsy was similar in those with a nuchal cord at birth (>34,000 patients) compared with no nuchal cord [51]. By contrast, a population-based case-control study of 271 singletons with spastic cerebral palsy and 217 controls without developmental disorders reported a 2.8-fold increased risk of spastic cerebral palsy in newborns with a nuchal cord (OR 2.8, 95% CI 1.31-6.02) [49]. (See "Cerebral palsy: Epidemiology, etiology, and prevention".)

Some authors have suggested that tightness of the nuchal cord is the key factor increasing the risk of adverse outcome as a tight cord may cause prolonged hypoxemia and acidosis. A retrospective study reported that a tight nuchal cord at delivery increased the odds of developing unexplained spastic quadriplegia (OR 18, 95% CI 6.2-48) [46]. Other presentations of nuchal cords, such as any or multiple entanglements, were not analyzed. However, tightness of the nuchal cord was not significantly associated with cerebral palsy in another retrospective study [49]. A retrospective study analyzing factors preceding neonatal hypoxic-ischemic encephalopathy (HIE) found that a tight nuchal cord was an independent risk factor for HIE (OR 2.8, 95% CI 1.02-7.8) [50].

The possible association of a tight nuchal cord with cerebral palsy in retrospective studies may be due to recording bias: Documentation of a tight nuchal cord may be more likely when the infant is born in a poor condition. In a study comparing elective versus systematic recording of nuchal cords in infants with low Apgar scores <7 at one minute, documentation of a tight nuchal cord was six times more likely with elective reporting than when recording was systematic [48]. Likewise, when the presence or absence of nuchal cords was recorded systematically, a significant association between nuchal cords or tight nuchal cords and cerebral palsy was not observed. Other reasons for debate about an association with cerebral palsy are the common occurrence of nuchal cords compared with cerebral palsy, the typically benign course of nuchal cords, multifactorial causality of cerebral palsy, and absence of standards regarding screening, diagnosis, and management of nuchal cords.

In a single large retrospective cohort study, rates of hospitalization in childhood/early adulthood due to cardiovascular or respiratory morbidity were similar among those with or without a history of a nuchal cord at birth [39].

PREGNANCY MANAGEMENT

Antepartum — An incidental finding of a nuchal cord on ultrasound examination does not warrant a change in prenatal care given the lack of evidence of a clinically significant increase in adverse pregnancy outcome (see 'Possible sequelae' above). However, when multiple (>3) nuchal cord loops are visualized, some clinicians recommend increased fetal surveillance with Doppler ultrasound and nonstress tests as well as planned delivery of term infants [19,52,53]. The harms and benefits of this approach have not been analyzed.

No randomized trials or prospective studies have compared potential approaches to management of pregnancies with nuchal cords diagnosed prenatally. A retrospective study compared the outcomes of 188 pregnancies with nuchal cords detected by sonography during the second and third trimesters with 115 pregnancies without prenatally detected nuchal cords [54]. At delivery, 37 percent of pregnancies with prenatally diagnosed nuchal cords had nuchal cords versus 15 percent of the control group. Both groups had similar perinatal outcomes and few adverse events. This study of nuchal cords diagnosed remote from delivery, although small and retrospective, affirms previous data of generally good outcomes of nuchal cords diagnosed closer to the time of delivery.

Breech presenting fetus — We do not perform cephalic external version and advise against an attempt at vaginal breech delivery if the fetus has a nuchal cord because we believe there may be an increased risk of complications during these procedures. However, due to the possibility that the nuchal cord will resolve before labor, we offer a follow-up ultrasound examination a few days later and proceed with version if the cord has disentangled [55].

There are sparse data on the management of breech presentations with a nuchal cord at the time of planned cephalic external version or planned vaginal birth [56,57], and no consensus on management of these patients. One study reported a decreased rate of successful external cephalic version in patients with nuchal cords (17.6 versus 53.6 percent) and a significant increase in fetal heart rate decelerations leading to interruption or abandonment of the procedure (82.3 versus 24.3 percent) [56].

During labor — The presence of a nuchal cord does not affect our intrapartum management. As discussed above, there is no strong evidence of a clinically significant increase in adverse pregnancy outcome (see 'Possible sequelae' above). In an observational study of pregnant patients with fetuses with nuchal cords, antepartum Doppler ultrasound of the nuchal cord had poor sensitivity and specificity for predicting intrapartum fetal distress necessitating cesarean birth [58].

As the fetal head descends or rotates, changes in the tightness of a nuchal cord may occur and may result in fetal heart rate decelerations, which should be managed as in any labor with fetal heart rate decelerations. (See "Intrapartum category I, II, and III fetal heart rate tracings: Management".)

Delivery — If a loose nuchal cord(s) is palpated after expulsion of the fetal head, it can usually be slipped over the head to free the fetus from the tether. If the cord(s) is too tight to easily slip over the head, it may be possible to slip it back over the shoulders and deliver the body through the loop.

These approaches may be unsuccessful if the cord is too tight. In these cases, it is important to avoid avulsing or tearing the cord while attempting to effect delivery. Occasionally, the body can be delivered without releasing the cord and without compromising the fetus. In most cases, we place a palm on the fetal occiput and push the face into the mother's thigh (or pubic bone), which allows the shoulders, then body, then legs to deliver (called "somersault maneuver" (figure 2)) [59,60]. The cord can then be unwrapped from the neck. In rare cases when this maneuver is not successful, the cord is doubly clamped and transected. However, early clamping and cord cutting decreases the volume of blood transferred from the placenta to the neonate, which may increase neonatal anemia, and may adversely affect the fetal to neonatal transition.

In monoamniotic twin pregnancies, clamping and cutting a tight nuchal cord on the first twin should be avoided since it may be the umbilical cord of the undelivered twin.

SUMMARY AND RECOMMENDATIONS

●Nuchal cords can occur as single or multiple entanglements around the fetal neck. They may be loose or tight. They have been classified as type A or B (figure 1). (See 'Classification' above.)

●The occurrence of a nuchal cord(s) appears to be a random event, with increased risk among fetuses with excessive movement and/or a long umbilical cord. (See 'Pathogenesis' above.)

●A nuchal cord can form at any gestational age, but appears to be more common at term. It may persist, disentangle, or reform. Type B nuchal cords are more likely to persist than type A nuchal cords (figure 1). (See 'Incidence' above and 'Natural history' above.)

●The prenatal diagnosis of an incidental nuchal cord is based on an ultrasound examination documenting that at least 75 percent of the neck is encircled by umbilical cord (movie 1 and movie 2). Color Doppler imaging or Doppler flow velocimetry (image 2) helps to confirm a diagnosis made by gray-scale imaging (image 1). The sensitivity of ultrasound for detecting nuchal cords at term has been reported to be approximately 70 percent for gray-scale imaging and 83 to 97 percent with color Doppler. (See 'Diagnostic evaluation and performance of ultrasound' above.)

●Although available data are of low to moderate quality, nuchal cords are associated with an increased rate of intrapartum fetal heart rate abnormalities leading to an increased rate of operative delivery. Single nuchal cords are not associated with stillbirth. Data for multiple nuchal cords are less clear. While there is a trend toward fetal growth restriction and small for gestational age infants, nuchal cords are not associated with birth weight <2500 grams. (See 'Possible sequelae' above.)

●We suggest not screening for nuchal cords during pregnancy (Grade 2C). There is no high or even moderate quality evidence that nuchal cords adversely affect pregnancy outcome or that prenatal diagnosis of nuchal cords improves pregnancy outcome. In cases of otherwise unexplained fetal compromise during pregnancy, assessment of the umbilical cord beyond standard evaluation, including assessment for a tight nuchal cord or multiple cords, may provide useful information to guide the degree of surveillance. (See 'Screening' above and 'Possible sequelae' above.)

●An incidental finding of a nuchal cord on ultrasound examination does not warrant a change in prenatal or intrapartum care, given the lack of evidence of a clinically significant increase in adverse pregnancy outcome. Detection of a complex nuchal cord entanglement (>3 loops, any combination with true knots or presence of a single umbilical artery) may warrant prudent follow-up.

We do not attempt external cephalic version of the breech fetus with a tight nuchal cord. (See 'Antepartum' above and 'During labor' above.)

●We do not report incidental detection of a nuchal cord, as it can be considered a normal finding. For patients who ask about a nuchal cord, we reassure the patient that a nuchal cord is a common finding that often resolves and that persistent nuchal cords have not been associated with a markedly increased risk of adverse pregnancy outcome. As in all pregnancies, the patient should be instructed to report decreased fetal movement to her provider. (See 'Screening' above.)

●If the cord is around the neck after expulsion of the fetal head, slipping the cord over the head or slipping it over the shoulders and delivering the body through the loop usually successfully frees the fetus from the tether. If delivery of the shoulders and body are compromised by a tight single or multiple nuchal cord that is not reducible, we perform a "somersault maneuver." If this is not successful, the cord may be clamped and cut. (See 'Delivery' above.)

●Fetal demise due to strangulation is rare. The presence of a nuchal cord alone is insufficient evidence of causality. The presence of the following findings supports causality in these rare cases (see 'Fetal or neonatal demise' above):

•One or more nuchal cords indenting fetal neck tissue.

•Petechial hemorrhages of the head and neck.

•Vascular congestion and thrombosis of umbilical cord vessels.

•Cord edema or hemorrhage into the Wharton jelly.

•Vascular ectasia, vascular thrombosis, and/or thrombotic vasculopathy (avascular villi, villous stromal karyorrhexis) involving the umbilical cord vessels and/or chorionic plate and stem villous vessels.

•Absence of other conditions associated with fetal demise.