A unicornuate uterus is a type of congenital uterine abnormality (müllerian duct abnormality). A unicornuate uterus is smaller than a typical uterus and usually has only one functioning fallopian tube. The other side of the uterus may have what is called a rudimentary horn.
A rudimentary horn is an underdeveloped “horn” on one side of the unicornuate uterus. About 65% of women with a unicornuate uterus have a rudimentary horn. The rudimentary horn may or may not be connected with the rest of the uterus and vagina.
In women with normal reproductive histories, about 2% to 4% are thought to have some sort of congenital anomaly. In women with a history of pregnancy loss or other adverse outcomes, about 5% to 10% have an anomaly and unicornuate uteri make up about 10% of the total number of diagnosed congenital uterine anomalies.
Imaging studies, such as HSG or ultrasound, may indicate that a woman most likely has a unicornuate uterus. A hysteroscopy, three-dimensional ultrasound or laparoscopy might also be used to confirm the diagnosis.
Researchers are experimenting with surgical treatment methods for the unicornuate uterus but right now the only generally accepted treatment is surgical removal of the rudimentary horn when needed (see below).
Having a unicornuate uterus unfortunately brings a significant risk of both pregnancy loss and preterm labor, as well as ectopic pregnancy. Estimates vary by specific study, but one literature review found pregnancy outcomes in women with unicornuate uteri to be miscarriage in 37%, preterm birth in 16%, and term birth in only 45%.
Doctors believe the miscarriage risk is due to abnormalities in the blood supply of the unicornuate uterus that might interfere with the functioning of the placenta (or increase the odds of implantation in the tube).
The risk of preterm labor is thought to be because of space restrictions; because a unicornuate uterus is smaller than a typical uterus, the growth of the baby might trigger early labor. Doctors may recommend cerclage for women at risk of preterm labor.
Women who have a rudimentary horn that connects with the rest of the uterus face additional risk. Because the rudimentary horn of the unicornuate uterus has considerable space restrictions, a pregnancy implanted there faces the possibility of rupture (similar to in ectopic pregnancies that implant in the fallopian tube). For this reason, doctors sometimes recommend surgery to remove the rudimentary horn.
Sources:
Heinonen, P.K., "Unicornuate uterus and rudimentary horn." Fertility and Sterility Aug 1997. 224-230. Accessed 7 Dec 2007.
Lin, Paul C. "Reproductive Outcomes in Women With Uterine Anomalies." Journal of Women's Health 2004. 33-39. Accessed 7 Dec 2007.
Maneschi, M., F. Maneschi, and G. Fuca, "Reproductive impairment of women with unicornuate uterus." Acta European Fertility. 1988. 273-275. Accessed 7 Dec 2007.
