a. Agenesis & hypoplasia: Mayer-Rokitansky-Kuster-Hauser syndrome is most common. All or part of the müllerian tract fails to form, or is extremely underdeveloped. For example, a cervix may be a tissue-thin membrane rather than a tough, fibrous "donut" several centimeters thick. Most women suffering from agenesis or extreme hypoplasia have severe fertility problems, simply by lacking sufficient tissue to support a growing pregnancy. A common diagnosis used to be "infantile uterus," but it simply means a smaller-than-average uterus and does not refer to the MA described above. The old "infantile uterus" is typically capable of supporting a pregnancy very well, since a uterus easily grows during pregnancy. The "infantile" term has fallen by the wayside in recent years.
b. Unicornuate uterus (UU): When one müllerian duct is underdeveloped or fails to develop, a banana-shaped half-uterus is formed. It may or may not be accompanied by a rudimentary horn, and that other horn may or may not have an endometrial cavity or communicate with the main uterine cavity. A missing kidney or other kidney problems accompany this asymmetric anomaly more than they do other MAs. Frequently, the ovary on the rudimentary side is found in an odd place, further up by the ribs. Adverse pregnancy outcomes are common with UU. SEE FIGURE BELOW.
c. Uterus didelphys (UD): The müllerian tract fails to fuse along all or most of its length. There may be complete duplication of the vagina, cervix and uterus, and the two halves may be divided by a ligament of connective tissue. UD is reported to have the best pregnancy outcomes of all the MAs. SEE IMAGE BELOW.
d. Bicornuate uterus (BU): The uterine fundus fails to fuse and a myometrial division extends down to the cervix in a complete bicornuate uterus, or part way to the cervix in a partial bicornuate uterus. The division is visible on the outside of the uterus, evidenced by a groove or cleft in the uterine dome exceeding 1.5 centimeters. Cervix and vagina are usually single but may be septate or duplicate. BU has relatively few pregnancy complications when compared to SU or UU, with breech presentation being one of the most common. SEE IMAGE BELOW.
e. Septate uterus (SU): The müllerian tract has fused properly and the uterus looks single from the outside, but the inner duct wall (i.e. the median septum) has failed to dissolve around 20 weeks of gestation, and the uterus retains a double cavity. There may or may not be a shallow groove of 1.5 centimeters or less on the outer uterine dome, and sometimes even a whitish triangle of tissue, the septum itself, is visible. The somewhat fibrous inner septum extends to the internal cervical opening or beyond in a complete septate uterus, and extends only part of the way down in a partial septate or subseptate uterus. The inadequate blood supply and progesterone receptors of the median septum may cause problems in pregnancy, giving the SU the worst pregnancy outcomes of all the MAs. SEE IMAGE BELOW.
f. Arcuate uterus (AU): The fundus of the uterus may be indented slightly both inside and outside. This shape has been variously defined as slightly bicornuate and slightly septate (and may be either one), and is so slight that it is considered a variation of normal. However, a few studies suggest that increased incidence of adverse pregnancy outcomes are associated with an arcuate uterus.
g. DES-related uterus: A T-shaped uterine cavity, dilated horns and malformed cervix and upper vagina may characterize this anomaly. Unlike the other anomalies, a T-shaped uterus is sometimes caused by maternal ingestion of DES, although sometimes the cause is unknown. When caused by DES, there are often other problems, such as incompetent cervix, infertility and abnormal tissue in the cervix and vagina. DES use is associated with high rates of female cancers, including cancer of the vagina.