Medical Editor: Jay W. Marks, MD

A couple of years ago an episode of the popular TV series Grey's Anatomy featured a woman with two uteruses (or uteri). This unusual condition does, in fact, occur as a result of abnormal fetal development. It has made the news again and it appears that a woman in Utah has two uteruses and is carrying a baby in each one.

The Mullerian ducts are two structures present in every embryo. During the ninth week of pregnancy, these structures fuse. While they largely disappear in males, the fused Mullerian ducts develop into the uterus, Fallopian tubes, and vagina in females. If this development does not proceed normally, abnormalities can occur in the genital tract that are often referred to as "fusion" or "duplication" abnormalities.

In women, abnormal development of the Mullerian ducts can lead to a condition known as uterus didelphys, in which the woman has a double set of reproductive tract organs - two each of the uterus, cervix, and vagina. In this case, one vaginal opening is usually blocked and the external appearance of the genitalia is normal.

Another condition known as uterus duplex bicollis occurs when a woman has two each of the uterus and cervix, but only one vagina. If there is doubling of the uterus but only one cervix and vagina, the condition is termed bicornuate uterus. It is also possible to have abnormal development in only one of the two Mullerian ducts, which can lead to an abnormality called unicornuate uterus , with only one normal Fallopian tube.

Because the external genitalia generally appear normal in these cases, the conditions may not be diagnosed at birth. However, sometimes an abdominal lump or mass is seen in newborn girls that may suggest the diagnosis. Women with uterus didelphys may be diagnosed at puberty when menstruation begins. Although menstruation is normal in these women, menstrual blood will build up in the blocked vagina, leading to pain and an abdominal mass.

Also because the external genitalia are normal, many cases of reproductive tract duplication or fusion are likely never diagnosed. For this reason, it is difficult to predict exactly how often these abnormalities occur.

Ultrasound, vaginoscopy (insertion of a scope into the vagina to view the internal anatomy), and hysterosalpingogram (HSG, an imaging procedure that involves injection of dye through the vagina into the uterus and Fallopian tubes) are all methods that may be used to establish the diagnosis of reproductive tract abnormalities. Treatment depends upon the individual anatomy and extent of the fusion or duplication. Complete duplication of the vagina is often treated by a simple surgical procedure to remove the septum (dividing wall between the two vaginas), allowing drainage of menstrual blood.

Duplication of the reproductive tract does not interfere with a woman's ability to become pregnant. However, the anatomical abnormalities may lead to complications of pregnancy such as incompetent cervix, breech or other abnormal fetal positions, and an increased incidence of miscarriage. Abnormalities in development of the reproductive tract can also be associated with congenital malformations of the kidneys and urinary system.

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