A bicornuate uterus is a uterus with two distinct cavities instead of one, giving it a heart shape rather than the typical pear shape. It’s a congenital condition, meaning it develops before birth and is present from the start. Most people with a bicornuate uterus don’t know they have one until it’s found during imaging for another reason, often a pregnancy or fertility workup.
How a Bicornuate Uterus Forms
During early fetal development, between the sixth and tenth weeks of pregnancy, two tube-like structures called the Müllerian ducts are supposed to fuse together to form a single uterine cavity. When that fusion is incomplete, the result is a uterus with two separate cavities divided by a wedge of tissue at the top. The bottom of the uterus typically fuses normally, so most people with this condition still have a single cervix and a single vagina.
There are two subtypes. In the more common form (bicornuate unicollis), the two cavities share one cervix. In a rarer form (bicornuate bicollis), both the upper and lower portions fail to fuse, resulting in two separate cavities and two cervices. The exact cause of the incomplete fusion isn’t well understood, but it isn’t something caused by anything the mother did during pregnancy.
Partial vs. Complete
The depth of the indentation at the top of the uterus determines whether a bicornuate uterus is classified as partial or complete. A partial bicornuate uterus has a mild dip, so the two cavities are less distinct. A complete bicornuate uterus has a deep separation, making the two “horns” more pronounced. The degree of separation can influence how much the condition affects pregnancy, with more pronounced division generally carrying higher risk.
Symptoms and How It’s Found
Many people with a bicornuate uterus have no symptoms at all. Some experience painful periods or heavier menstrual bleeding, but these symptoms are common enough that they rarely prompt suspicion of a uterine anomaly on their own. More often, the condition is discovered incidentally during a pelvic ultrasound, or it comes to attention after recurrent miscarriages or preterm deliveries.
A standard two-dimensional ultrasound can raise suspicion, but it isn’t always enough to confirm the diagnosis. Three-dimensional ultrasound and MRI are better at showing the external shape of the uterus, which is the key detail. The distinction matters because a bicornuate uterus looks similar to a septate uterus on basic imaging, yet the two conditions are treated very differently. In a septate uterus, the outer surface of the uterus is flat or convex with a shallow concavity of less than 1 centimeter, while a bicornuate uterus has a deep external cleft. MRI is considered the gold standard for telling them apart.
Impact on Fertility and Conception
One of the first questions people ask after diagnosis is whether they’ll be able to get pregnant. The reassuring answer is that a bicornuate uterus does not appear to significantly reduce your ability to conceive. A study comparing women with a bicornuate uterus to women with a normally shaped uterus during IVF treatment found no meaningful difference in embryo implantation rates (about 33% vs. 43%), clinical pregnancy rates, or cumulative live birth rates (58% vs. 65%). The ovarian response to fertility treatment was also comparable between the two groups.
In other words, the condition primarily affects the ability to carry a pregnancy rather than the ability to become pregnant in the first place.
Pregnancy Risks
Where a bicornuate uterus does make a difference is during pregnancy. Because each cavity is smaller than a single normal cavity, the growing baby has less room. This can lead to several complications.
- Preterm birth: The restricted space can trigger early labor, and preterm delivery is the most commonly reported complication.
- Miscarriage: Recurrent pregnancy loss is more common, particularly in the second trimester, likely because of reduced blood supply or space constraints as the pregnancy grows.
- Breech or abnormal positioning: Research on pregnancies in bicornuate uteruses shows breech presentation rates between roughly 35% and 46%, compared to about 3% to 4% in the general population at term. The unusual shape of the cavity limits the baby’s ability to turn head-down.
- Cesarean delivery: Partly because of malpresentation and partly because of other risk factors, cesarean delivery rates are higher. In one study, about 73% of deliveries in women with a bicornuate uterus were by cesarean.
Not every pregnancy in a bicornuate uterus is high-risk. Many people carry to term and deliver healthy babies, especially with closer monitoring. The severity of the uterine division plays a role: a mild partial indentation may cause few or no problems, while a deep complete separation is more likely to affect the pregnancy.
How It Differs From a Septate Uterus
This distinction comes up constantly in diagnosis and matters for treatment. Both conditions create a divided uterine cavity, but the underlying anatomy is different. A septate uterus has a normal outer shape with a wall of tissue (septum) hanging down inside. A bicornuate uterus has an abnormal outer shape, with a visible cleft or notch on the outside of the uterus that creates two horns.
Why does this matter? A septum inside an otherwise normal uterus can be removed with a relatively straightforward procedure done through the cervix. A bicornuate uterus involves the actual muscular wall of the uterus, so correction requires a more involved open surgery. Getting the diagnosis right avoids unnecessary or inappropriate procedures.
Treatment Options
If you have a bicornuate uterus and no symptoms or pregnancy complications, treatment is typically not needed. The condition itself doesn’t require correction just because it exists.
Surgery becomes a consideration for people who have experienced recurrent pregnancy loss or repeated preterm deliveries that are attributed to the uterine shape. The procedure used is called a Strassman metroplasty, which involves surgically joining the two cavities into one. This is an abdominal surgery, not a minimally invasive one, and it requires a recovery period of several months before attempting pregnancy. A future pregnancy after this surgery almost always requires delivery by cesarean because the uterine wall has been surgically altered.
For those who don’t pursue surgery, pregnancy management focuses on closer surveillance. This typically means more frequent ultrasounds to monitor the baby’s growth and position, along with careful attention to signs of preterm labor. A cervical cerclage, a stitch placed in the cervix to help keep it closed, is sometimes used if there’s concern about cervical weakness contributing to early delivery.