Dr.  Anthony Shaya, MD, MPH, FACOG, of Partners in Women’s Health, answered some questions about this rare uterine malformation.

What is a “unicorn uterus”?  A unicornuate uterus is when there is only one side or one horn to the uterus.  Cornu means horn in latin.  The other side (meaning the other horn) is either very small or completely absent.

How does it happen?  A brief course on embryology is needed.  The uterus normally forms from two ducts, the mullerian ducts.  In the womb, early in gestation, these two ducts will form on either side of the female fetus in the lower abdominal region.  Normally the uterus is formed when the two ducts come from either side and meet in the middle during growth and development of the fetus.   If only one duct forms initially, then there will be only one side of the uterus that will form, resulting in a a unicornuate uterus.

How common is it?   It is fairly rare, around 1/4000 women.  It is just one of different types of uterine malformations that can occur.

What are the symptoms of a unicorn uterus, if any?   There may be no symptoms.  Or some patients might not be able to conceive or have painful menses.  Also, patients might not be able to carry a pregnancy and could suffer from recurrent miscarriages.

How does a woman typically discover that she has it?   A woman would typically find out because she cannot get pregnant.  In the testing process, one of the tests will evaluate the uterine shape, and this would be discovered at that time.  Some patients may not know, conceive, go to term, and then it could be discovered in a c-section.

Is it possible to get pregnant and have a baby when you have a unicorn uterus?   Yes, and many times patients might conceive, have a baby and never know.  But it is also possible that patients with this condition might suffer from infertility.

Are there any complications or concerns with having this condition?   As stated above, infertility and painful menses can be an issue.  One other important issue is that sometimes patients with a unicornuate uterus can also have anomalies in the kidneys and urine collecting system.