A unicornuate uterus is an unusually shaped uterus caused by errors during embryonic development. In a person with a unicornuate uterus, only half of the uterus has fully formed, with a single “horn” leading to one of the fallopian tubes. This condition is very rare. People can successfully get pregnant with this uterine abnormality, although having a unicornuate uterus does increase the risk of pregnancy complications, including pregnancy loss.
During embryonic development, two structures known as the Mullerian ducts eventually develop into the uterus. In some fetuses, only one duct fully develops. Unicornuate uteri can be variable in appearance. Sometimes, the undeveloped duct creates a sealed partial uterus. In some women, a partial second horn can be observed, although it is usually not connected to the fallopian tube.
This uterine abnormality is sometimes not diagnosed until a pregnant woman experiences complications and needs a Cesarean section. As soon as she is opened up in the operating room, the unusual shape of the uterus will be readily apparent. In other women, the anomaly may be noted during surgical procedures in the abdomen, including procedures like tubal ligations.
Having a unicornuate uterus can lead to fertility issues. Women who have difficulty conceiving may be run through a series of tests to determine the cause. If these tests include imaging studies of the uterus, the woman's unusually shaped uterus may become visible. However, imaging studies cannot always reliably pick up a unicornuate uterus.
Women with this congenital disorder are at risk of pregnancy complications because the uterus is smaller, and it is possible for the pregnancy to implant in a bad location, potentially leading to rupture. Pregnant women who know they have unicornuate uteri should make sure their obstetricians are aware so plans can be made to keep the pregnancy as safe as possible. Something else to be aware of with this anomaly is that sometimes a kidney is missing or misshapen as well. This can require taking some special precautions to maintain kidney health in the remaining fully functional kidney.
The causes of unicornuate uterus formation are not fully understood. In some cases, environmental exposures during embryonic development can lead to anatomical abnormalities. In other instances, there are no known risk factors for anomalies or it is difficult to identify risk factors because the uterine abnormality is identified so late, it is difficult to get accurate information about environmental exposures during the patient's embryonic development.