What are congenital uterine abnormalities?

About 3 in 100 women are born with an abnormality in the size, shape or structure of the uterus. In the female embryo, the uterus is formed from two small tubes called Mullerian ducts. At about 10 weeks gestation, these two tubes come together and fuse, forming a single uterine cavity. When the Mullerian ducts do not fuse at all or fuse incompletely, a uterine abnormality can result.

Some women with a congenital uterine abnormality have normal, full-term pregnancies. However, these abnormalities can increase the risk of a number of reproductive problems, including:
• Miscarriage (pregnancy loss that occurs before 20 weeks of pregnancy)
• Premature birth
• Poor fetal growth
• Abnormal presentation, such as breech position (the baby is in a position other than head down)
• Cesarean birth
The risk may be different for each one of these problems, depending on the specific uterine abnormality.

Congenital uterine abnormalities include:
Septate uterus. This is the most common congenital uterine abnormality and is most commonly associated with adverse pregnancy outcomes, especially miscarriage. In a septate uterus, the uterus is divided into two sections by a band of muscle or tissue. This tissue is the remainder of the joined Mullerian tubes, which the body did not break down and absorb as it should have.
Bicornate uterus. In this condition, the uterus has two partially or completely joined cavities, instead of one large cavity. This abnormality is caused by incomplete fusion of the Mullerian tubes.
Didelphic uterus (double uterus). The Mullerian tubes fail to join, resulting in two separate uterine cavities and two cervices. Each uterine cavity may be smaller than normal.
Unicornate uterus. One Mullerian duct fails to form, resulting in absence of half of the uterus.

For more information, including diagnosis and treatment of uterine abnormalities, read our article.

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