Children's Hospital Colorado

Müllerian Anomalies

What is a Müllerian anomaly?

The Müllerian structures are the structures found in the female fetus that eventually develop into a woman's reproductive organs. These structures were named after German physiologist Johannes Petrus Müller.

During typical fetal development, two tube-like structures called the Müllerian ducts fuse together to create the uterus, fallopian tubes and majority of the vagina. When one of these structures does not fully develop, a malformation of the uterus or vagina occurs, and this is referred to as a Müllerian anomaly. An anomaly that affects the uterus is called a uterine anomaly.

The various malformations are categorized based on the portion of the uterus or vagina that does not form properly, known as:

  • Septate uterus: The external shape of the uterus is normal, but the cavity is divided by an extra wall of tissue called a septum, which runs down the middle of the cavity. If the septum completely divides the cavity, it is known as a septate uterus; if it partially divides the cavity, it is known as a sub-septate uterus.
  • Bicornuate uterus: The external shape of the uterus is abnormal with a large indentation in the fundus (the top of the uterus), which causes the upper cavity to further divide into two cavities. This is a result of the two Müllerian ducts only partially fusing together.
  • Unicornuate uterus: Only half of the uterus develops, which is the result of only one Müllerian duct developing.
  • Uterine didelphys: The entire uterus and cervix is duplicated (also called a didelphic uterus), which creates two uteri and two cervices. The patient still has the standard two fallopian tubes and two ovaries. This condition is the result of the two Müllerian ducts developing, but not fusing together at all.
Mullerian Anomalies

What causes a Müllerian anomaly?

Doctors don't completely understand the cause of Müllerian anomalies. They are considered multifactorial, meaning they are likely caused by defects in multiple genes, with some influence from factors in our environment. The reproductive organs begin to develop when the mother is about six weeks pregnant, while an early fetus is developing inside the mother's womb, or uterus.

The reproductive organs begin to develop when the two Müllerian ducts start to migrate toward each other and begin to fuse in the middle of the fetus. Typically, some of the tissue migrates upwards to form the uterus and fallopian tubes, and the remaining tissue migrates downwards to form the vagina. Any disruption in this process may result in a malformation of the uterus, vagina, or both, which leads to a Müllerian anomaly.

Who gets a Müllerian anomaly?

These malformations can happen to any woman, and they occur in about 3 to 5% of the general population. There are no specific known risk factors that cause this condition.