A human bicornuate uterus
|Classification and external resources|
A bicornuate uterus or bicornate uterus (from the Latin cornū, meaning "horn"), commonly referred to as a "heart-shaped" uterus, is a uterus composed of two "horns" separated by a septum. In humans, a bicornuate uterus is a type of uterine malformation, but in some other mammalian species, including rodents and pigs, it is normal.
A bicornuate uterus is formed during embryogenesis. The fusion process of the upper part of the paramesonephric ducts is altered. As a result, the lower part of the uterus is unitary while the upper part is bifurcated.
It is possible to diagnose a bicornuate uterus using gynecologic ultrasonography, specifically sonohysterography, and MRI. However, as there is no indication to do such procedures on asymptomatic women, the presence of a bicornuate uterus may not be detected until pregnancy or delivery. In a C-section (usually done due to malpresentation), the irregular shape of the uterus will be apparent.
There are many degrees of a bicornuate uterus. There is a continuous range of the degree and location of the fusion of the paramesonephric ducts, and existence of a spectrum, rather than a fixed number of types corresponding to strict medical definitions. Two processes that occur during the embryonic development of the paramesonephric ducts — fusion and reabsorption — can be affected to different degrees. This degree of fusion and reabsorption can determine the likeliness of a pregnancy reaching full term.
There is also a hybrid bicornuate uterus: External fundal depressions of variable depths associated with a septate uterus can be seen by laparoscopy, indicating the coexistence of the two anomalies. These cases are candidates for hysteroscopic metroplasty under appropriate sonographic and/or laparoscopic monitoring.
An obstructed bicornuate uterus showing uni or bilateral obstruction might also be possible. The unilateral obstruction is more difficult to diagnose than the bilateral obstructive. A delay in the diagnosis can be problematic and compromise the reproductive abilities of those cases.
The occurrence of all types of paramesonephric duct abnormalities in women is estimated around 0.4%. A bicornuate uterus is estimated to occur in 0.1-0.5% of women in the U.S. It is possible that this figure is an underestimate, since subtle abnormalities often go undetected. Some intersex individuals whose external genitalia are perceived as being male may nonetheless have a variably shaped uterus.
Effect on pregnancy
Pregnancies in a bicornuate uterus are usually considered high risk and require extra monitoring because of association with poor reproduction potential.
A bicornuate uterus is associated with increased adverse reproductive outcomes, such as:
- Recurrent pregnancy loss
- Preterm birth: The rate of preterm delivery is 15 to 25%. A pregnancy may not reach full term in a bicornuate uterus when the baby begins to grow in either of the uterine horns. A short cervical length seems to be a good predictor of preterm delivery in women with a bicornuate uterus.
- Malpresentation (breech birth or transverse presentation): a breech presentation occurs in 40-50% of pregnancies with a partial bicornuate uterus and not at all (0%) in a complete bicornuate uterus.
- Deformity: Offspring of mothers with a bicornuate uterus are at high risk for "deformities and disruptions" and "malformations."
Effect on intrauterine device usage
Usage of intrauterine device (IUD) with copper requires one IUD in each horn to be effective in case of bicornuate uterus. The same practice is generally applied when using IUD with progestogen due to lack of evidence of efficacy with only one IUD.
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