A unicornuate uterus is a uterus that has a single horn and a banana shape. Approximately 65% of women with a unicornuate uterus also have a second smaller or rudimentary uterine horn. The rudimentary horn can be solid or it can have a small cavity with a functioning endometrium. Sometimes the smaller horn connects to the uterus and vagina, but more often it is isolated or non-communicating.
A unicornuate uterus is the least common congenital uterine anomaly and represents 1 to 2% of cases. A unicornuate uterus can be asymptomatic. However, women with a functioning non-communicating horn may experience pain during periods, because there is no outlet for the menstrual fluid. Women with a unicornuate uterus are at risk of reproductive complications. They may have a difficult time becoming pregnant because typically only one fallopian tube functions. In fact the condition is sometimes first discovered when a women undergoes an infertility investigation.
Pregnancy can occur with a unicornuate uterus, and the term pregnancy rate is approximately 47%. But women with a unicornuate uterus who do become pregnant are at risk of: Spontaneous abortion - it is thought that the abnormal shape of the uterus itself and compromised blood flow to the uterus and placenta lead to spontaneous abortion.
Premature labor - since the uterine cavity is smaller than usual, the baby outgrows the available space earlier in the pregnancy and there is an increase in breech presentation during delivery.
Surgical correction of a unicornuate uterus is not possible, as the uterus can not be enlarged. Cervical cerclage may be recommended for women with a unicornuate uterus who have experienced miscarriages or premature births. Pregnancy can also occur in a non-communicating arm. The situation is similar to an ectopic pregnancy and must be treated as an emergency. If pregnancy occurs in the non-communicating arm, uterine rupture occurs in approximately 89% of cases by the end of the second trimester. Because of this risk, surgical removal of the non-communicating arm is recommended. Removal of a solid non-functioning arm is not necessary.
It is difficult to diagnose a unicornuate uterus with ultrasound. The condition can be visualized with MRI, three-dimensional sonography and with laparoscopy.
No surgical intervention is required unless endometrial tissue in a rudimentary horn results in pain or a pelvic mass or unless an incompetent cervix is suspected during pregnancy. A rudimentary horn may be excised to treat endometriosis and prevent an ectopic pregnancy. Cervical cerclage may be recommended during pregnancy in women with a history of miscarriage and/or premature birth or if an incompetent cervix is observed.