What is a molar pregnancy?

A molar pregnancy is a genetically abnormal pregnancy; due to an error at conception, the fertilized egg has too many chromosomes. Most molar pregnancies are complete moles (no fetal tissue), but occasionally, a partial mole occurs (containing some fetal tissue). Because of this genetic defect, placental tissue begins to grow very erratically, producing large amounts of pregnancy hormone (HCG).

Molar pregnancy is potentially dangerous. Rarely, the placental tissue becomes cancerous (choriocarcinoma). This occurs about 1 per 40,000 pregnancies. Choriocarcinoma (also known as gestational trophoblastic disease) can be treated and usually cured with chemotherapy.

A molar pregnancy must be removed by a D&C. Because of the small risk of cancer, a woman must be monitored closely for a year to be sure that cancer does not develop. The best way to monitor for choriocarcinoma is to check the level of HCG (pregnancy hormone). Since a normal pregnancy will also produce HCG,a woman who has had a molar pregnancy will be advised to prevent pregnancy for an entire year by using birth control pills. She will have weekly HCG tests done until the level returns to normal and then less frequent tests for the remainder of the year.