transverse-presentation

Bicornuate uterus

A bicornuate uterus, commonly referred to as a "heart-shaped" uterus, is a type of an uterine malformation where two "horns" form at the upper part of the uterus.

Pathophysiology

A bicornuate uterus is formed during embryogenesis. The fusion process of the upper part of the Müllerian ducts is altered. As a result the caudal part of the uterus is normal while the cranial part is bifurcated.

Classification

There are many degrees of a bicornuate uterus. There is a continuous range of the degree and location of the Müllerian ducts fusion and existence of a septum rather than a fixed number of types corresponding to strict medical definitions. Two processes that occur during the embryonic development of the Müllerian ducts, fusion and reabsorption, can be affected to different degrees. The degree can determine the likeliness of a pregnancy reaching full-term.

Epidemiology

The occurrence of all types of müllerian 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 is an underestimate since saddle abnormalities often go undetected.

Effect on reproduction

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 like:

1. Recurrent pregnancy loss. The reproductive potential of a bicornuate uterus is usually measured by live birth rate (also called fetal survival rate). This rate is estimated around 63% for a bicornuate uterus.

2. Preterm delivery. With a 15 -25% rate of preterm delivery. The reason that a pregnancy may not reach full-term in a bicornuate uterus often happens when the baby begins to grow in either of the protrusions at the top. A short cervical length seems to be a good predictor of preterm delivery in women with a bicurnuate uterus.

3. Malpresentation (breech birth or transverse presentation). A breech presentation occurs in 40-50% pregnancies with a partial bicornuate uterus and not at all (0%) in complete bicornuate uterus.


Previously, a bicornuate uterus was thought to be associated with infertility , but recent studies have not confirmed such an association.

Diagnosis

It is very difficult, though sometimes possible, to diagnose a bicornuate uterus using an ultrasound. As a result, a bicornuate uterus often goes undetected until delivery. In a c-section (usually done due to malpresentation) the irregular shape of the uterus can be noticed. Imaging detection methods include: hysterosalpingography and hysteroscopy. MRI is emerging as an accurate detection method for bicornuate uterus as well as other Müllerian duct abnormalities.

References

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