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Molar Pregnancy


Updated June 30, 2014

Pregnant woman holding teddy bear
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A molar pregnancy refers to a pregnancy that is a type of gestational trophoblastic disease (GTD). It can refer to either a complete or a partial mole. While there are regional differences, the rate of molar pregnancy is about 1/1000 to 1/1500. We still do not know exactly why a molar pregnancy occurs. It is believed to be a nutritional deficit, like protein or carotene. It can also be caused by a ovular (ovulation) defect.

Women at Risk

  • Over 50 years
  • Clomiphene stimulation (Clomid)
  • 1-2% chance of a second mole
  • Early Teens

Complete Mole

This occurs when the nucleus of an egg is either lost or inactivated. The sperm then duplicates itself because the egg was lacking genetic information. Usually there is no fetus, no placenta, no fluid and no amniotic membranes.

The uterus is rather filled with the mole that resembles a bunch of grapes. The fluid filled vesicles grow rapidly, which can make the uterus seem larger than it should be for gestational age. Because there is no placenta to receive the blood typically you will see bleeding into the uterine cavity or vaginal bleeding.

Partial Mole

This most frequently occurs when two sperm fertilize the same egg. There may be partial placentas, membranes or even a fetus present in a partial mole. However, there are usually genetic problems with the baby. Rarely, a partial mole will exist with twin pregnancy, however, the other twin rarely survives.


Symptoms include:

  • Increased nausea and vomiting
  • Vaginal bleeding
  • Increased hCG levels
  • Rapidly growing uterus
  • Pregnancy induced hypertension prior to 24 weeks
  • No fetal movement or heart tone detected
  • Hyperthyroidism
  • Pulmonary Embolism


Most of the time a molar pregnancy will spontaneously end. When the woman passes tissues that appear to be grape like and shows them to her practitioner then a molar pregnancy is suspected.

Ultrasound can also help determine a molar pregnancy. When doing an ultrasound one sees a "snow storm effect" on the screen.

Serial hCG levels can show a rapid rise in hCG that may indicate that further study is needed.

Molar Pregnancy Video

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