A septate uterus is a congenital condition where a wall of tissue, called a septum, hangs down inside the uterus and partially or fully divides the cavity into two sections. It forms before birth, during fetal development, when the tissue that normally dissolves to create a single open uterine cavity fails to be fully absorbed. It’s the most common structural uterine anomaly, affecting roughly 1 to 3% of women in the general population, with estimates climbing to 3 to 15% among women experiencing infertility or recurrent miscarriage.
How a Septate Uterus Forms
During early fetal development, the uterus starts as two separate tubes that fuse together. Once fused, the tissue wall between them is supposed to dissolve, leaving behind one open chamber. In a septate uterus, that middle wall doesn’t fully break down. What remains is a wedge of fibrous or muscular tissue projecting downward from the top of the uterus.
The outer shape of the uterus looks completely normal. This is a key distinction from other uterine anomalies. The problem is entirely internal, which is why the condition often goes undetected for years.
Partial vs. Complete Septum
The European Society of Human Reproduction and Embryology classifies a septate uterus as having an internal indentation at the top of the uterine cavity that exceeds 50% of the uterine wall thickness, while the outer contour remains normal. Within that definition, there are two types:
- Partial septate uterus: The septum extends partway down the cavity but doesn’t reach the cervix. This is the more common form.
- Complete septate uterus: The septum runs the full length of the cavity, all the way down to the cervical opening, effectively creating two separate channels.
The exact prevalence numbers vary widely depending on which diagnostic criteria are used. One large study of reproductive-age women found that using the European society’s criteria identified a septate uterus in 13.5% of women, while applying the American Society for Reproductive Medicine’s stricter criteria identified it in only 0.9 to 1.4%. This discrepancy matters because it affects who gets diagnosed and who gets offered treatment.
Symptoms and How It’s Found
Most women with a septate uterus have no symptoms at all. It doesn’t typically cause pain, and it shouldn’t change your period in terms of flow, timing, or cramping. Many people live with one their entire lives without knowing.
The condition is most often discovered when a woman is being evaluated for recurrent miscarriages or difficulty getting pregnant. Sometimes it’s found incidentally during imaging for an unrelated reason. Because there are no outward signs, the diagnosis almost always comes from a detailed look at the uterine cavity.
How It’s Diagnosed
Distinguishing a septate uterus from a bicornuate uterus (where the uterus itself is divided into two horns with an abnormal outer shape) is critical because the two conditions are managed very differently. On a basic ultrasound, both can look similar: two endometrial cavities appear on the screen. The difference is whether the outside of the uterus is smooth and normal (septate) or has a deep indentation or cleft at the top (bicornuate).
Three-dimensional transvaginal ultrasound is currently the most practical and accurate noninvasive tool. When combined with saline infusion to expand the cavity, it reaches 100% accuracy compared to the historical gold standard of combined laparoscopy and hysteroscopy. Even without saline, 3D ultrasound is over 88% accurate across multiple studies. Standard 2D ultrasound, MRI, and hysteroscopy alone are all less reliable at making the distinction on their own, according to the American Society for Reproductive Medicine’s 2024 guidelines.
Impact on Pregnancy
This is the part most people searching for this topic care about, and the numbers are striking. Women with an untreated septate uterus have a live birth rate around 37.9%, compared to roughly 84.8% in women without the anomaly. Miscarriage rates range from 36 to 77%, far above the typical 9 to 17% background rate.
The septum causes problems for a few reasons. The tissue of the septum has a poor blood supply compared to normal uterine lining, so an embryo that implants on or near the septum may not get adequate nourishment. The septum can also physically restrict the growing baby’s movement, increasing the risk of abnormal positioning. In one surgical study, 80.6% of pregnancies before treatment ended in early miscarriage, and 66.7% of those that continued resulted in preterm delivery.
Not every septate uterus leads to pregnancy loss. Some women carry to term without any intervention, particularly if the septum is small or the embryo implants on a well-vascularized part of the uterine wall. But the statistical risk is high enough that the condition is taken seriously in the context of reproductive planning.
Surgical Treatment
The standard treatment is a hysteroscopic metroplasty, a minimally invasive procedure done through the cervix with no external incisions. A thin camera is passed into the uterus, and the septum is cut using one of several tools: cold scissors, a bipolar or monopolar electrode on a resectoscope, or occasionally a laser. There is no current evidence strongly favoring one instrument over another.
When bipolar energy is used, the uterus is distended with normal saline, which carries a lower risk of fluid-related complications than the sugar-based solutions needed for monopolar instruments. The procedure is typically outpatient, and recovery is relatively quick compared to open surgery.
The results can be dramatic. In one study tracking the same women before and after surgery, the live birth rate jumped from 3.7% to 84.6%. Early miscarriage dropped from 80.6% to 8.8%, and preterm delivery fell from 66.7% to 7.0%. When researchers excluded women who had additional complicating conditions like adhesions, polyps, or endometriosis, preterm birth rates after surgery dropped even further, to 4.8%.
Septate vs. Bicornuate Uterus
These two conditions are frequently confused, and the distinction matters enormously. A septate uterus has a normal external shape with an internal dividing wall. A bicornuate uterus has two actual horns, with a visible indentation on the outer surface of the uterus. On imaging, the double endometrial cavities sit closer together in a septate uterus and are more widely spaced in a bicornuate one.
The reason this matters is treatment. A septate uterus can be corrected with a relatively simple hysteroscopic procedure. A bicornuate uterus, if it requires intervention at all, would need a much more invasive abdominal surgery. Misdiagnosing one as the other could lead to either unnecessary major surgery or a missed opportunity for a straightforward fix. This is why 3D imaging that shows both the inside and the outside of the uterus is so valuable for getting the diagnosis right.