What is Unicornuate Uterus?

Learn the Definition of This Condition—and How it May Affect a Pregnancy

Doctors examining pregnant woman
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What a Unicornuate Uterus Is:

A uterus is an organ in a woman's body that's often called the womb. It's the place in which a fertilized egg is supposed to implant and then grow into a baby. A unicornuate uterus is a type of congenital uterine abnormality (müllerian duct abnormality). A unicornuate uterus is smaller than a typical uterus (often about half the normal size and usually has only one functioning fallopian tube (rather than two).

The other side of the uterus may have what is called a rudimentary horn.

What a Rudimentary Horn Is:

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.

If the rudimentary horn is not connected to the rest of the uterus and vagina, then a woman may experience very painful periods because the menstrual blood becomes backed up. If the rudimentary horn is connected to the rest of the uterus and vagina, or if a woman doesn't have a rudimentary horn, then a woman may not experience any symptoms throughout her lifetime until she begins trying to conceive. At that point, she may experience difficulty getting and staying pregnant (more on that later). 

Unicornuate Uterus Statistics:

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 a congenital anomaly and unicornuate uteri make up about 10% of the total number of diagnosed congenital uterine anomalies.

Diagnosing Unicornuate Uterus:

Imaging studies, such as hysterosalpingogram (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.

Treatment Options:

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).

What a Unicornuate Uterus Means for Miscarriage and Pregnancy Loss Risks:

Having a unicornuate uterus, unfortunately, brings a significant risk of both pregnancy loss and preterm labor, as well as ectopic pregnancy (that's when a fertilized egg implants outside the uterus—usually in the fallopian tubes—and must be terminated). Estimates vary by 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 45%.

Doctors believe that the higher 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 fallopian tube).

The higher risk of preterm labor exists because of space restrictions; since a unicornuate uterus is smaller than a typical uterus, the growth of the baby might trigger early labor. Doctors may recommend a surgical procedure called cerclage for women at risk of preterm labor—it's a procedure in which the cervix is sewn closed during pregnancy. 

Women who have a rudimentary horn that connects with the rest of the uterus face additional risk. Since the rudimentary horn of the unicornuate uterus has considerable space restrictions, a fertilized egg that's implanted there faces the possibility of rupture (similar to ectopic pregnancies that implant in a fallopian tube). For this reason, doctors sometimes recommend surgery to remove the rudimentary horn.


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.


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