Version May 2024
INTRODUCTION — Congenital uterine anomalies (CUAs) may lead to symptoms such as pelvic pain, prolonged or otherwise abnormal bleeding at the time of menarche, recurrent pregnancy loss, or preterm birth, and thus may be identified in patients, including adolescents, who present with these disorders. Some CUAs may be suspected because of associated findings on physical examination, such as a longitudinal vaginal septum. Others may be detected when imaging studies are performed to evaluate patients with infertility, symptoms related to nonreproductive organ systems, or trauma.
The classification, diagnosis, and clinical manifestations of major congenital anomalies of the corpus (septate, unicornuate, bicornuate, and didelphys uterus) along with their potential associated cervical and vaginal anomalies will be reviewed here. Treatment of these anomalies is discussed separately. (See "Congenital uterine anomalies: Surgical repair".)
Cervical agenesis/hypoplasia, congenital vaginal abnormalities, and diethylstilbestrol (DES)-related anomalies are also reviewed separately. (See "Congenital anomalies of the hymen and vagina" and "Outcome and follow-up of diethylstilbestrol (DES) exposed individuals" and "Benign cervical lesions and congenital anomalies of the cervix", section on 'Agenesis/hypoplasia'.)
CLASSIFICATION — There is no universally accepted classification system for CUAs, which is problematic because such a system would allow physicians to codify the symptomatology, treatment, and outcome of affected patients and more accurately compare their research data with that of others [1].
●The American Society for Reproductive Medicine's (ASRM, formerly the American Fertility Society) classification system for müllerian defects has been the standard in the United States for decades (figure 1A-B) [2,3]. The 2021 system emphasizes CUA and associated anomalies of the vagina, cervix, fallopian tubes, and renal system and utilizes descriptive terminology rather than the previous number system. The descriptive terminology includes: müllerian agenesis, cervical agenesis, unicornuate uterus, uterus didelphys, bicornuate uterus, septate uterus, longitudinal vaginal septum, transverse vaginal septum, and other complex anomalies.
●The European Society of Human Reproduction and Embryology (ESHRE) and the European Society for Gynaecological Endoscopy (ESGE) have published their own classification system (figure 2A-B) [4].
●Other classification systems have also been proposed to further clarify the vast array of complex anomalies, and include Acien's classification (table 1) [5] and Congenital Uterine Malformation by Experts [6].
ASSOCIATED ANOMALIES IN OTHER ORGAN SYSTEMS — Patients with CUAs are at increased risk of having renal, skeletal, or abdominal wall abnormalities, or a history of inguinal hernia, and vice versa.
Renal anomalies are found in 20 to 30 percent of patients with müllerian defects [7-9]. Duplex collecting system, horseshoe kidney, pelvic kidney, and unilateral renal agenesis have been associated with an obstructed hemiuterus, obstructed hemivagina, and transverse vaginal septa. When a renal anomaly is present, it is typically ipsilateral to the CUA. For example, a patient with an obstructed hemiuterus on the left and a normal right hemiuterus will have an abnormal left and a normal right kidney.
PREVALENCE — An accurate prevalence of CUAs is difficult to determine since many are never identified, especially if they are asymptomatic. Reported prevalence varies depending on the population studied.
●In a systematic review, the prevalence of CUAs was 5.5 percent in an unselected population, 8 percent in infertile patients, 12.3 percent in patients with a history of miscarriage, and 24.5 percent in patients with miscarriage and infertility [10].
●In a series of 5590 females with renal anomalies, 29 percent were found to have müllerian anomalies [9].
●In a well-designed study of nearly 700 patients with normal reproductive outcomes who were evaluated with laparoscopy or laparotomy prior to tubal ligation and then underwent a hysterosalpingogram five months after sterilization, the prevalence of CUAs was 3.2 percent [11].
●In another study, the prevalence of CUAs was 5 to 10 percent among patients with recurrent first trimester miscarriage and over 25 percent among those with late first trimester-second trimester miscarriage/preterm birth [12].
The prevalence of CUAs in patients with primary infertility is not increased; it is approximately the same as that in fertile patients with normal reproductive outcomes [13].
Frequency of specific CUAs in affected patients — In a literature review of studies including infertile and fertile patients with CUAs, the frequencies of specific anomalies were: septate (35 percent), bicornuate (26 percent), arcuate (18 percent), unicornuate (10 percent), didelphys (8 percent), and agenesis (3 percent) [13]. However, these frequencies can vary substantially depending upon the specific population studied and the methodology used to identify the abnormalities. In the well-designed study of patients with normal reproductive outcomes described above, the frequencies were: septate (90 percent), bicornuate (5 percent), and didelphic (5 percent) [11].
PATHOGENESIS
Normal uterine development — The müllerian ducts are first identifiable at approximately six weeks of gestation when they begin to elongate caudally and cross the metanephric ducts medially to meet in the midline. By the seventh week, the urorectal septum has developed and separates the rectum from the urogenital sinus. Around 12 weeks, the caudal portion of the müllerian ducts fuse to form the uterovaginal canal, which inserts into the dorsal wall of the urogenital sinus at Müller's tubercle. The two müllerian ducts are initially composed of solid tissue and lie side by side. Subsequently, internal canalization of each duct produces two channels divided by a septum that is absorbed in a cephalad direction by 20 weeks. The cranial, unfused portions of the müllerian ducts develop into the fimbria and fallopian tubes, while the caudal, fused portions form the uterus and upper vagina (figure 3).
Abnormal uterine development — The underlying etiology for abnormal uterine development is not well understood. Most defects are likely to be related to polygenic and multifactorial causes. The karyotype of patients with uterine anomalies is usually normal (46,XX) [14].
The three main mechanisms for abnormal uterine development are agenesis/hypoplasia, defective lateral fusion, and defective vertical fusion.
●Agenesis or hypoplasia – Müllerian agenesis or hypoplasia leads to variable uterine development and congenital absence of the vagina, termed the Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome. The resulting uterus may consist of lateral hemi-uteri or uterine horns (eg, unicornuate uterus), or a midline uterus without a cervix, or, most commonly, it may not develop at all. (See "Congenital anomalies of the hymen and vagina", section on 'Vaginal agenesis (Mayer-Rokitansky-Kuster-Hauser syndrome)'.)
●Lateral fusion defect – Defective lateral fusion leads to development of organs that are either symmetric or asymmetric, and nonobstructed or obstructed (eg, bicornuate uterus, uterus didelphys). One or more of the following can lead to a lateral fusion defect:
•Failure of resorption resulting in a uterine or longitudinal vaginal septum
•Failure of formation of one of the two müllerian ducts
•Failure of duct migration
•Failure of müllerian ducts fusion
●Vertical fusion defect – Defective vertical fusion leads to development of a transverse vaginal septum, segmental vaginal agenesis, and/or cervical agenesis or dysgenesis. The vagina and/or cervix may be nonobstructed or obstructed. It results from either defective fusion of the caudal end of the müllerian duct and urogenital sinus or from defective vaginal canalization. (See "Congenital anomalies of the hymen and vagina" and "Benign cervical lesions and congenital anomalies of the cervix".)
In addition, in utero exposure to diethylstilbestrol (DES), a synthetic estrogen used to prevent pregnancy loss from 1949 to 1971, is associated with a variety of female genital tract anomalies, including:
●Uterine anomalies (T-shaped uterine cavity, hypoplastic uterus, midfundal constrictions, filling defects, and endometrial cavity adhesions (figure 4A-C)).
●Vaginal adenosis, vaginal ridges, transverse septa.
●Cervical anomalies including hypoplasia, hoods, collars, or pseudopolyps.
POTENTIAL CONSEQUENCES — In nonpregnant patients, CUAs that obstruct or partially obstruct the flow of menses (eg, noncommunicating functioning uterine horn, uterine duplication with an obstructed hemivagina, uterine septum with an obstructed hemivagina (figure 5)) can lead to:
●Hematometra (blood-filled uterine cavity)
●Hematocolpos (blood-filled vagina)
●Retromenstruation and development of endometriosis
●Pelvic pain, cyclic or noncyclic
●Abnormal uterine bleeding or discharge
●Genital tract infection
CUAs typically do not prevent conception and implantation, either spontaneous or after in vitro fertilization [15-18].
In pregnant patients, CUAs have been associated with [13,18-27]:
●Spontaneous abortion
●Recurrent miscarriage
●Preterm birth
●Prelabor rupture of membranes
●Intrauterine growth restriction
●Antepartum and postpartum bleeding
●Placental attachment abnormalities
●Cervical insufficiency
●Fetal malpresentation
●Pregnancy-associated hypertension
●Cesarean birth
●Rupture of a rudimentary horn
Various hypotheses have been proposed to explain these associations. For example, malpresentation and, in turn, cesarean birth may be related to the small uterine cavity of the anomalous uterus, which may inhibit fetal movement to cephalic presentation. Vaginal septa may also be a reason for cesarean birth [28]. Growth restriction may be related to abnormal uterine vasculature. Postpartum hemorrhage may result from the placenta becoming partially trapped in an accessory horn or a placental attachment abnormality. Pregnancy-associated hypertension has been attributed to coexistent congenital renal abnormalities [23]. Pregnancy loss may be related to implantation at an unfavorable site, such as a septum [13].
The types and frequencies of obstetric complications associated with specific CUAs vary among reports. In the most recent systematic review, compared with normal uteri, patients with CUAs were at increased risk for [27]:
●Preterm birth – septate (odds ratio [OR] 4.06), bicorporeal (OR 4.98), hemi-uterus (OR 3.74)
●Malpresentation – septate (OR 13.76), bicorporeal (OR 10.41), hemi-uterus (OR 11.6)
●Cesarean birth – septate (OR 5.19), bicorporeal (OR 7.82), hemi-uterus (OR 2.06)
●Prelabor rupture of membranes – septate (OR 1.44), bicorporeal (OR 2.11), hemi-uterus (OR 1.54)
●Fetal growth restriction – septate (OR 2.99), bicorporeal (OR 3.86), hemi-uterus (OR 4.43)
●Placental abruption – septate (OR 10.7), bicorporeal (OR 7.61), hemi-uterus (OR 9.76)
In an earlier systematic review, patients with CUAs compared with normal uteri were also found to have increases in pooled relative risks (RR) for [18]:
●First-trimester spontaneous abortion – septate (RR 2.65), bicornuate (RR 2.32)
●Second-trimester spontaneous abortion – septate (RR 2.95), bicornuate (RR 2.90)
CLINICAL PRESENTATION — Many patients are asymptomatic. In some cases, findings on a routine physical examination may lead to further evaluation and diagnosis. Longitudinal vaginal septa and double cervixes are typically associated with uterine anomalies, such as uterus didelphys and some septate uteruses [29,30]. Each cervix is smaller than normal and palpable on either side of the vaginal septum (uterus may be septate or subseptate). The two cervixes may be located at different depths and are not exactly symmetric. Patients with hematocolpos or hematometra due to obstruction may have a palpable mass on bimanual examination.
Symptomatic patients may present with pain, abnormal vaginal bleeding, and/or infection. The presentation varies depending upon the defects involved.
●Patients with obstructive developmental anomalies of the müllerian duct may present with cyclic or chronic pelvic pain beginning at menarche. (See 'Uterus didelphys' below and 'Unicornuate uterus' below.)
●Patients with complete obstruction of the müllerian duct will have amenorrhea, and those with partial obstruction may present with hypomenorrhea. (See 'Uterus didelphys' below and 'Unicornuate uterus' below.)
●Patients with a transverse vaginal septum with a small fenestration may present with prolonged menstrual bleeding due to the inability of the normal menstrual flow to be expelled from the partially obstructed upper vagina. (See "Congenital anomalies of the hymen and vagina", section on 'Transverse vaginal septum'.)
●Microperforations in a transverse vaginal septum or obstructed hemivagina allow organisms to infect the hematocolpos. These patients may present with profuse, foul-smelling vaginal discharge. Rarely, the upper genital tract becomes infected, resulting in "cyclic pelvic inflammatory disease." (See "Congenital anomalies of the hymen and vagina", section on 'Transverse vaginal septum' and "Congenital anomalies of the hymen and vagina", section on 'Obstructed hemivagina'.)
●Patients with a longitudinal vaginal septum may present with vaginal bleeding despite use of a tampon: they need two tampons, one in each vagina. They may also complain of dyspareunia. (See "Congenital anomalies of the hymen and vagina", section on 'Longitudinal vaginal septum'.)
In other cases, the CUA is diagnosed incidentally on imaging studies or as a result of imaging studies for evaluation of a gynecologic problem or adverse pregnancy outcome (eg, during work-up of infertility, pelvic mass, pelvic pain, or recurrent pregnancy loss) [31], or as part of the evaluation of a female patient with renal, skeletal, or abdominal wall abnormalities, or a history of inguinal hernia [32]. (See 'Diagnosis and clinical significance of common CUAs' below and 'Associated anomalies in other organ systems' above.)
DIAGNOSTIC TOOLS — When a CUA is suspected, evaluation and diagnosis are based on imaging. Two-dimensional (2D) ultrasound is the initial imaging modality of choice because it is widely available, noninvasive, relatively inexpensive, provides information about relevant nonuterine structures (ovaries, kidneys, pelvic mass), and may provide information that can be helpful for choosing the subsequent imaging modality or modalities for definitive diagnosis. Three-dimensional (3D) reconstructed images provide more detailed information and often obviate the need for additional imaging [33-38].
Magnetic resonance imaging (MRI) has been the historic "gold standard" for diagnosing anomalies of the reproductive tract [39-42], but is reserved for those cases where 2D and 3D ultrasound findings are limited, and where a definitive diagnosis would alter patient care.
In patients with complicated müllerian anomalies, additional information may be obtained if clinically indicated by examination under anesthesia, vaginoscopy, laparoscopy, and/or hysteroscopy [41,43].
Ultrasonography — A key diagnostic goal when a uterine anomaly is suspected is to differentiate between a septate and a bicornuate uterus (see 'Septate or subseptate uterus' below and 'Bicornuate uterus' below). In addition, we routinely evaluate the kidneys of patients with müllerian defects with ultrasound, given the high frequency of renal abnormalities in these patients.
●Two-dimensional ultrasonography provides some information about the internal and external uterine contours. Performing the examination in the secretory phase of the menstrual cycle improves visualization of the endometrium. A longitudinal division that separates the endometrial echo from the fundus towards the cervix suggests duplication. 3D ultrasonography will show the uterine cavity, myometrium, and the external contour of the uterus in a single image, and can reliably differentiate between septate and bicornuate uteri [38,44-47]. The only limitation of 3D ultrasonography is that it is performed transvaginally and may not be tolerated by a nonsexually active adult, younger adolescent, or child.
Ultrasonography is also useful for detecting hematometra or hematocolpos.
●Saline infusion sonohysterography or hysterosalpingography (HSG) (see 'Hysterosalpingography' below) provides better information about the interior contour of the uterine cavity and can be helpful for assessment of the length/width of a uterine septum when planning the type of surgical resection [48,49]. (See "Saline infusion sonohysterography".)
Hysterosalpingography — HSG provides excellent information about the interior contour of the uterine cavity (image 1 and image 2), but not the external uterine contour, so it cannot distinguish between septate and bicornuate uteri. It will assist in determining if the fallopian tubes are patent. After an anomaly has been diagnosed, HSG can be helpful in evaluating possible complex communications involving the uterus and vagina and between uterine horns [41]. When two cervixes are present, the procedure needs to be done with injection of dye into both cavities, which can be accomplished with catheters in each hemiuterus (image 3). (See "Hysterosalpingography".)
Magnetic resonance imaging — MRI without contrast provides excellent delineation of both internal and external uterine contours and can differentiate septate from bicornuate uteri. MRI is very useful in determining the presence or absence of a cervix in a complex anomaly, or the presence of functioning endometrium in the case of a noncommunicating obstructed rudimentary uterine horn; however, MRI may not be able to identify a rudimentary uterine horn if it is located laterally along the psoas muscle and pelvic sidewall [50].
A normal unestrogenized prepubertal uterus is small and may be difficult to identify on imaging, even with MRI, which can lead to an inappropriate diagnosis of uterine agenesis.
DIAGNOSIS AND CLINICAL SIGNIFICANCE OF COMMON CUAs
Arcuate/normal uterus — An arcuate uterus has a slight midline indentation with minimal, and often broad, fundal cavity indentation (figure 6 and image 1); it is typically classified as a normal variant and is not associated with adverse pregnancy outcome.
Diagnosis — Arcuate uterus is suggested at ultrasound when the depth from the interstitial line to the apex of the fundal indentation is ≤1 cm and the angle of indentation is >90 degrees (figure 1B) [3]. 3D ultrasound can be helpful in confirming the diagnosis.
Clinical significance — Although previously believed to have clinical significance, an arcuate uterus is now considered to be a normal variant [7,13,17,19,44,51-53]. Patients are asymptomatic, have no compromise of fertility, and similar pregnancy outcomes as those in the general obstetric population.
Septate or subseptate uterus — The septate uterus is the most common uterine anomaly, accounting for 35 to 90 percent of all identified uterine malformations [11,13,54]. The septum consists of myometrium covered by endometrium and is usually vascularized [55]. In some studies, the endometrium covering the septum showed differences in histologic composition and gene expression compared with the normal uterine wall.
The etiology of a uterine septum is not clearly understood but can be hypothesized to occur either from a defect in canalization of the two fused müllerian ducts or from a defect in resorption of the midline septum between the two müllerian ducts. The degree of septation varies widely from a partial midline septum (a uterus with a partial septum is referred to as a subseptate uterus) (figure 7) with one cervix to complete failure of resorption resulting in a longitudinal septum that begins at the fundus, extends into the vagina (figure 8A-B), and is associated with two cervixes.
Whether a uterine septum is complete or incomplete (septate or subseptate uterus) is defined by the proximity of the septum to the internal os [56]. The thickness and composition of the septum, the relative amounts of fibrous and muscular tissue, and the degree of vascularization from the adjacent uterine wall may also vary. No classification system standardizes all of these variations.
Diagnosis — The diagnosis is typically based on ultrasound findings of two closely separated endometrial cavities and a smooth fundal contour (by contrast, the bicornuate uterus has an indented fundus) (image 4). The depth from the interstitial line to the apex of the indentation is >1 cm, and the angle of indentation is <90 degrees (figure 1B) [3]. The septum separating the endometrial cavity is usually thin and of variable length and may extend into the cervix (image 5) and vagina (longitudinal vaginal septum). However, definitions vary [57].
The sensitivity and specificity of magnetic resonance imaging (MRI) for diagnosis of septate uterus has been reported to be as high as 100 percent [41] since MRI clearly shows whether the contour of the fundus is smooth (septate uterus) or indented (bicornuate uterus). MRI can be helpful if 2D transabdominal ultrasonography is inconclusive and 3D ultrasonography cannot be performed. In cases of a large, wide, and deep septum, the appearance of the septum on MRI may help with surgical planning since it is the fibrous portion of the septum that is typically removed hysteroscopically.
Clinical significance — The septate uterus is more likely to be associated with adverse pregnancy outcome than other uterine anomalies. However, no clear biological basis for impaired reproductive outcomes in affected patients has been found [55].
Patients with septate uterus are at increased risk for spontaneous abortion (21 to 44 percent) and preterm birth (12 to 33 percent); the live birth rate ranges from 50 to 72 percent [13,22,56]. There appears to be a higher risk of recurrent miscarriage associated with longer septa, but this is controversial, and many untreated patients have good pregnancy outcomes. Pregnancy loss, when present, often occurs in the second trimester and may be distinguished from cervical insufficiency because of signs of labor [58]. The septate uterus is also associated with an increased risk of breech presentation [58] and abruption [18].
A septum that extends into the vagina and causes an obstructed hemivagina can lead to cyclic pain, a lateral vaginal mass, and, if the obstructed hemivagina is perforated, spotting or purulent vaginal discharge if the contents become infected. Sepsis has been reported [59].
Resection of the septum hysteroscopically (hysteroscopic metroplasty) can improve pregnancy outcome [60]. (See "Congenital uterine anomalies: Surgical repair", section on 'Septate uterus'.)
Bicornuate uterus — A bicornuate uterus has a fundus that is indented >1 cm (figure 1A) [3], and the vagina and cervix are generally normal (typically one cervix is present) [44]. It results from partial rather than complete fusion of the müllerian ducts. Depending on the extent of fusion, separation of the uterine horns will be complete (figure 9), partial (figure 10), or minimal [2].
Diagnosis — The diagnosis is based on ultrasound findings of two usually moderately separated (ie, divergent) endometrial cavities and an indented fundal contour (figure 1A and image 6 and image 7). As discussed above, 3D ultrasonography can reliably differentiate between septate and bicornuate uteri as it can simultaneously visualize both the external (serosal surface) and internal (uterine cavity) contours of the uterine fundus.
MRI is rarely needed to make a definitive diagnosis and should be reserved for times when 3D ultrasonography is not available or not tolerated by the patient, the results are inconclusive, or in cases with suspected complex anomalies involving multiple systems.
Clinical significance — Literature reviews have reported spontaneous abortion in 36 percent, preterm birth in 21 to 23 percent, and fetal survival in 50 to 60 percent of patients with a bicornuate uterus [13,22,61]. Fetal growth restriction and malpresentation in labor are also increased [18].
In patients with poor pregnancy outcomes that are thought to be related to the anomaly, uterine reunification can be performed via laparotomy. Due to an association between bicornuate uterus and cervical insufficiency, the cervical length should be assessed during pregnancy. (See "Congenital uterine anomalies: Surgical repair" and "Short cervix before 24 weeks: Screening and management in singleton pregnancies".)
Uterus didelphys — Uterus didelphys, or double uterus, is a duplication of the reproductive structures (figure 1A). Generally the duplication is limited to the uterus and cervix (uterine didelphys and bicollis [two cervixes]) (picture 1A-C), although duplication of the vulva, bladder, urethra, vagina, and anus may also occur. Fifteen to 20 percent of patients with didelphic uterus also have unilateral anomalies, such as an obstructed hemivagina and ipsilateral renal agenesis; the anomalies are on the right in 65 percent of cases [62]. Uterine didelphys occurs when the two müllerian ducts fail to fuse.
Diagnosis — Diagnosis is typically made by a combination of ultrasound showing two widely separated uterine horns with a deep fundal indentation (image 8 and image 9) and speculum examination showing two cervixes. MRI is rarely needed to make a definitive diagnosis.
Clinical significance — Spontaneous abortion rates of 32 percent and preterm birth rates of 28 percent have been reported in patients with uterus didelphys [13,22]. Fetal growth restriction also appears to be increased [18]. A septated vagina is present in 75 percent of cases and may cause difficulty with sexual intercourse or vaginal birth, which are reasons that affected patients may opt for resection of the vaginal septum. Metroplasty should be considered for patients with pelvic pain, recurrent miscarriages, or a history of preterm birth. (See "Congenital uterine anomalies: Surgical repair".)
Patients with an obstructed hemivagina and ipsilateral renal agenesis/anomaly (figure 11) will have regular menses because menstrual blood from one uterus can egress through its nonobstructed cervix and hemivagina [63]. However, such patients will most likely develop cyclic pain due to buildup of blood in the obstructed hemivagina [64]. In addition, there may be a microcommunication between the patent vagina and the obstructed vagina, resulting in an infected obstructed hemivagina. Bilateral complete obstruction is also possible and presents with primary amenorrhea (figure 12).
Treatment involves resection of the wall of the obstructed vagina followed by creation of a single vaginal vault. (See "Congenital uterine anomalies: Surgical repair".)
We, and others [7,65], do not believe that abdominal repair of the didelphic uterus to improve pregnancy outcome is sufficiently supported by existing data.
Unicornuate uterus — In the unicornuate uterus (figure 13), one cavity is usually normal, with a fallopian tube and cervix, while the failed müllerian duct has various configurations (figure 1A and figure 14A-E). The affected müllerian duct may not develop at all, or it may develop only partially as either a rudimentary horn on the uterus or an anlage (a cluster of embryonic cells). This horn (or anlage) may or may not communicate with the uterus.
Diagnosis — Diagnosis is typically made by ultrasound, showing a uterus deviated to one side of the pelvis; 3D-reconstructed images are particularly helpful (image 10). Care should be taken to assess for the presence of a noncommunicating or rudimentary horn.
In complicated cases where surgical removal is being considered for a rudimentary horn, MRI can be helpful in surgical planning.
Clinical significance — Most rudimentary horns are asymptomatic. Some contain functional, but not necessarily normal [66], endometrium that is shed cyclically. If a rudimentary horn is obstructed (without communication to the other uterus or cervix), the patient may develop cyclic or chronic abdominopelvic pain and may require surgical excision of the obstructed horn. In a literature review, the mean age of presentation was the mid-20s [66].
Patients with a unicornuate uterus are at higher risk for endometriosis, preterm labor, and breech presentation. A review of pregnancy outcomes in patients with unicornuate uteri had the following rates of obstetric complications: 2.7 percent ectopic pregnancy, 24.3 percent first-trimester abortion, 9.7 percent second-trimester abortion, 20.1 percent preterm birth, 3.8 percent fetal demise, and 51.5 percent live births [19].
Uterine rupture and/or placental attachment abnormalities (eg, accreta, increta, percreta) are associated with pregnancies in an obstructed or rudimentary uterine horn [66-73]. As an example, a study of 328 pregnancies in obstructed horns found that only 1 percent of such pregnancies were alive at term and 89 percent of the horns ruptured [68]. Both spontaneous rupture and rupture during labor or induction have been reported. Thus, such pregnancies should be immediately terminated.
Unicornuate uterus can be associated with an ectopic ovary, which is of clinical importance in patients undergoing ovulation induction or who develop ovarian neoplasms [74,75]. Ectopic ovaries have been identified using MRI.
Unicornuate uterus is associated with a particularly high incidence (40 percent) of renal abnormalities [76].
Patients with unicornuate uteri are generally not candidates for reconstructive procedures to improve pregnancy outcome, given that this anomaly is associated with generally favorable pregnancy outcomes [5]. However, a rudimentary horn with functioning endometrium can harbor an ectopic pregnancy, and thus noncommunicating rudimentary horns with endometrium are at times surgically removed.
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Congenital female reproductive tract anomalies".)
SUMMARY AND RECOMMENDATIONS
●Classification – Congenital uterine anomalies (CUAs) include septate, bicornuate, arcuate, unicornuate, didelphys, and agenesis. There is no universally accepted classification system for CUAs. The American Society for Reproductive Medicine 2021 classification system for müllerian defects is the revised standard in the United States (figure 1A-B). Other classification systems are presented in the figures (figure 2A-B). (See 'Classification' above.)
●Associated anomalies – Patients with CUAs are at increased risk of having renal, skeletal, or abdominal wall abnormalities, or a history of inguinal hernia and vice versa. (See 'Associated anomalies in other organ systems' above.)
●Prevalence – The prevalence of CUAs depends on the population studied. In a systematic review, the prevalence was 5.5 percent in an unselected population, 8 percent in infertile patients, 12.3 percent in patients with a history of miscarriage, and 24.5 percent in patients with miscarriage and infertility. A subsequent series including patients with renal anomalies found that 29 percent of such patients also had müllerian anomalies. (See 'Prevalence' above.)
Septate uterus is the most common CUA. (See 'Frequency of specific CUAs in affected patients' above.)
●Pathogenesis – The underlying etiology of congenital müllerian defects is not well understood. The karyotype of patients with these anomalies is usually normal. (See 'Pathogenesis' above.)
●Clinical presentation – Many patients are asymptomatic. In some cases, findings such as a vaginal septum, double cervix, or pelvic mass on a routine physical examination may lead to further evaluation and diagnosis. Symptomatic patients may present with cyclic or noncyclic pain, abnormal vaginal bleeding, and/or infection. In other cases, the anomaly is diagnosed incidentally on imaging studies, as a result of imaging studies for evaluation of a gynecologic problem or adverse pregnancy outcome, or as part of the evaluation of a female patient with renal, skeletal, or abdominal wall abnormalities, or a history of inguinal hernia. (See 'Clinical presentation' above.)
●Potential consequences – In nonpregnant patients, CUAs can lead to hematometra, hematocolpos, retromenstruation, pelvic pain, abnormal uterine bleeding, or genital tract infection. The ability to conceive a pregnancy is not typically impaired. (See 'Potential consequences' above.)
●Diagnostic tools
•Most patients undergo two-dimensional ultrasound examination as the initial imaging modality. It also provides information about relevant nonuterine structures (eg, ovaries, kidneys). (See 'Ultrasonography' above.)
•Three-dimensional ultrasound is helpful to assess the outer contour of the fundus (ie, differentiate between a septate and a bicornuate uterus) (figure 1A-B). Hysterosalpingography provides information about fallopian tube patency and size and configuration of the uterine cavity or cavities. Saline infusion sonohysterography and hysterosalpingography both delineate the uterine cavity well. (See 'Diagnostic tools' above.)
•In complicated cases, magnetic resonance imaging may be needed to better clarify complex anomalies; it is also helpful for younger patients who cannot tolerate or decline a vaginal probe three-dimensional (3D) ultrasonography. (See 'Magnetic resonance imaging' above.)
ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Ronald E Iverson, Jr, MD, who contributed to an earlier version of this topic review.
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