Bicornuate Uterus
A bicornuate uterus is a heart-shaped uterus, formed when the two tubes that create the organ during fetal development fuse at the bottom but not at the top. The result is a single lower uterus with two separate upper horns and a visible indentation in the outer surface. Most women with one have no symptoms and conceive normally, and many discover it only during a scan in pregnancy or an investigation for something else. Its significance lies in pregnancy rather than fertility: the reduced and unusually shaped space is associated with a higher chance of preterm birth and of the baby lying breech. Crucially, it is different from a septate uterus—a distinction that determines whether surgery is even an option.
What is it?
Early in fetal development, the uterus forms from a pair of structures called the Müllerian ducts. These migrate toward the midline and fuse together from the bottom upward, creating a single organ. In a bicornuate uterus, that fusion is incomplete: the lower portion joins normally, but the upper portion remains separate, leaving two horns and a cleft in the outer surface of the uterus at the top.
The characteristic appearance is often described as heart-shaped. From the outside, the top of the uterus is indented rather than smoothly rounded. From the inside, the cavity divides into two narrower horns, each leading to a fallopian tube.
The degree varies considerably. A bicornuate unicollis uterus has two horns above but a single cervix below. A bicornuate bicollis uterus has two cervices as well, and this configuration is frequently accompanied by a septum dividing the upper vagina. Milder versions shade toward what is classified as an arcuate uterus, which is a shallow indentation generally regarded as a normal variant with little or no reproductive significance.
The distinction that matters most in this entire area is between a bicornuate and a septate uterus, and it is worth understanding precisely because the two are constantly confused—including, historically, by clinicians.
Both produce a divided cavity. The difference lies entirely in the outside of the uterus. In a bicornuate uterus, the outer surface is indented, because the two halves never fused at the top; the division is a genuine external separation. In a septate uterus, the outside is smooth and normal, and the division is caused by a wall of tissue left behind inside an otherwise normally formed uterus.
This distinction determines what can be done. A septum sits inside the cavity and can be divided through the cervix using a hysteroscope, in a short day-case procedure with no incision. A bicornuate uterus cannot be corrected that way—there is nothing inside to remove, and attempting to cut the tissue between the horns would perforate straight through the wall into the abdomen. Correcting it requires opening the abdomen and reconstructing the uterus, a substantially more serious undertaking.
Before three-dimensional imaging was widely available, this distinction was frequently got wrong, because the common tests of the era—hysterosalpingography and two-dimensional ultrasound—show only the cavity. Women were sometimes told they had one when they had the other, and some underwent unnecessary surgery. This is the principal reason modern assessment requires imaging that shows both the cavity and the external contour.
The cause is unknown in almost all cases. The condition arises sporadically during early fetal development, is not inherited in any predictable pattern, and is not caused by anything a mother did or was exposed to during pregnancy—a reassurance worth stating explicitly, since women sometimes assume otherwise. There is a modest familial tendency, but most women have no affected relatives.
Because the reproductive and urinary systems develop from closely related tissue at the same time, abnormalities of the kidneys and urinary tract occur more frequently in women with uterine anomalies. Kidney imaging is therefore recommended when the diagnosis is made, since a missing or abnormal kidney has implications well beyond reproductive care.
Most women with a bicornuate uterus have no symptoms whatsoever, and a substantial number never learn they have one.
Where symptoms occur, painful periods are the most commonly reported, and some women describe heavier bleeding or pelvic discomfort. Where a vaginal septum accompanies the anomaly, difficulty inserting tampons, tampons failing to control bleeding because a second passage is present, or discomfort during intercourse may be noticed.
The condition most often comes to attention through pregnancy—either during a routine scan, or through the reproductive effects described below.
Those reproductive effects deserve accurate rather than alarming description, because information available online frequently overstates them.
Fertility is generally not impaired. Women with a bicornuate uterus conceive at broadly normal rates, and the condition is not in itself a cause of difficulty becoming pregnant. This is worth stating clearly, because a common assumption after diagnosis is that conception will be difficult.
Miscarriage risk is modestly increased compared with a normally shaped uterus, though considerably less so than with a septate uterus. Most pregnancies in women with a bicornuate uterus proceed normally.
Preterm birth is the most consistently reported association and is the main clinical concern. The reduced and irregularly shaped cavity provides less room as pregnancy advances, and this appears to contribute to earlier labour.
Abnormal fetal position is notably more common. The shape of the cavity tends to constrain how a baby can lie, and breech or transverse presentation occurs considerably more often than in a normally shaped uterus. This is the main reason caesarean rates are higher—not because the uterus itself requires it, but because the baby is more often positioned in a way that makes vaginal birth unsuitable.
Fetal growth restriction occurs somewhat more frequently, and in some women the placenta implants in a less favourable position.
The overall picture is of a raised but not prohibitive risk. The great majority of women with a bicornuate uterus who become pregnant have a living, healthy baby, and many have entirely uncomplicated pregnancies. The purpose of knowing the diagnosis is to allow appropriate monitoring, not to create expectation of difficulty.
Diagnosis requires imaging that shows both the inside and the outside of the uterus.
Three-dimensional transvaginal ultrasound is the preferred first-line test. It reconstructs the uterus in a plane that displays the cavity and the outer contour simultaneously, and specific measurements of the depth of the external indentation are used to classify the anomaly. In experienced hands it is accurate enough to make the diagnosis confidently without further testing.
MRI provides detailed assessment of the uterus, cervix, and vagina, is used where ultrasound is inconclusive or the anatomy is complex, is valuable before any surgery, and images the kidneys in the same examination.
Two-dimensional ultrasound may raise the suspicion by showing two separate cavities, particularly during pregnancy, but cannot confirm which anomaly is present.
Hysterosalpingography demonstrates a divided cavity and remains useful for assessing whether the fallopian tubes are open during fertility investigation, but it cannot distinguish bicornuate from septate and should not be used alone for that purpose.
Laparoscopy allows the outer contour to be seen directly and was historically combined with hysteroscopy to resolve the question. It is now rarely needed for diagnosis alone.
Kidney ultrasound is recommended alongside the diagnosis.
A practical note: a bicornuate uterus is sometimes first suspected during early pregnancy, when a scan shows the pregnancy in one horn and a thickened lining in the other, which can be mistaken for a second sac or for a mass. Clarifying the anatomy usually resolves this, though definitive classification is often deferred until after pregnancy when the uterus can be assessed properly.
Important to Know
The message most women with this diagnosis need is that a bicornuate uterus is a variation in shape rather than a disease, that it usually requires no treatment, and that most affected women have successful pregnancies. Care is typically coordinated by gynaecologists and, during pregnancy, obstetric teams.
Surgery is rarely appropriate. The operation to unify a bicornuate uterus—a Strassman metroplasty—involves opening the abdomen, incising the uterus between the two horns, and reconstructing it as a single cavity. It is major surgery with significant recovery, leaves a scarred uterus that generally necessitates delivery by caesarean section and carries a risk of rupture in labour, and the evidence that it improves outcomes is limited and largely historical. It is reserved for women with repeated pregnancy losses where thorough investigation has found no other cause, and even then it warrants careful discussion. A woman offered this operation on the basis of the diagnosis alone, without a history of recurrent loss, would be right to seek a second opinion.
Pregnancy management centres on monitoring rather than intervention. Typical care includes scans to check fetal growth, attention to fetal position in later pregnancy, and discussion of delivery planning. Cervical length monitoring is used in some settings to identify women at higher risk of preterm birth. Awareness of the higher chance of preterm labour means women are generally advised on the symptoms to report and where to go, which allows treatment to be given early if labour does begin prematurely.
Cervical cerclage—a stitch placed to support the cervix—is not recommended simply because a woman has a bicornuate uterus. It is considered where there is demonstrated cervical weakness, typically on the basis of previous mid-trimester loss or a short cervix on scanning, and the decision is individualised.
Delivery planning is individualised. A vaginal birth is entirely possible where the baby is head-down and there are no other concerns, and the diagnosis alone is not an indication for caesarean section. Higher caesarean rates reflect the increased frequency of breech and transverse positions rather than a requirement of the anomaly itself.
Attempting to turn a breech baby externally is less likely to succeed where the uterine shape constrains movement, and this is factored into planning.
Fertility treatment, where needed for unrelated reasons, proceeds normally. In vitro fertilisation is not affected by the diagnosis in any fundamental way, though some clinicians favour transferring a single embryo, since a twin pregnancy in a reduced cavity carries additional risk.
A coexisting vaginal septum causing difficulty with tampons or intercourse is straightforward to remove, and this is worth asking about if those symptoms are present, since it is easily overlooked once attention focuses on the uterus.
Kidney assessment should be arranged when the diagnosis is made. A missing or malformed kidney affects medication choices, blood pressure management, and long-term health monitoring, and identifying it has value independent of anything reproductive.
The psychological dimension deserves acknowledgement. Being told the uterus is an unusual shape, often during pregnancy or while trying to conceive, can be frightening, and online information frequently emphasises complications without context. The accurate picture is that most women with a bicornuate uterus who want children have them. Where a woman has experienced losses, the diagnosis can also bring a difficult mix of explanation and self-blame, and support is worth seeking rather than managing alone.
Care is coordinated by gynaecology and obstetrics, with maternal-fetal medicine involvement where there is a history of preterm birth or recurrent loss. Imaging findings are interpreted alongside reproductive history and plans rather than in isolation, and the specific classification of the anomaly should be confirmed with three-dimensional imaging or MRI rather than accepted from older test results.
Patient education plays an important role. Understanding that fertility is usually normal, that most pregnancies succeed, that the main risks are preterm birth and breech position rather than inability to carry a pregnancy, that surgery is rarely appropriate, and that the distinction from a septate uterus determines what options exist all contribute to appropriate care and considerably less anxiety.
Red flag symptoms include regular painful contractions, a persistent low backache with pelvic pressure, or a change in vaginal discharge before 37 weeks of pregnancy, which may indicate preterm labour and requires immediate assessment; any leaking of fluid from the vagina in pregnancy; vaginal bleeding in pregnancy; reduced or absent fetal movements; severe abdominal pain in pregnancy; severe, progressively worsening cyclical pelvic pain, particularly in an adolescent, which may indicate an obstructed anomaly; and severe pain with dizziness or fainting in early pregnancy. These warrant urgent medical assessment.