Molar pregnancy: What are the causes?

What causes a molar pregnancy? Does a molar pregnancy increase the risk of future miscarriages?

- Courtney / Kentucky

Mayo Clinic obstetrician and gynecologist Roger Harms, M.D., and colleagues answer select questions from readers.

Answer

A molar pregnancy, also called gestational trophoblastic disease, is an abnormality of the placenta caused by a problem at fertilization. In a molar pregnancy, the early placenta develops into a fast-growing mass of cysts (hydatidiform mole) in the uterus. Molar pregnancy is a type of miscarriage complicated by a noncancerous (benign) tumor.

There are two types of molar pregnancies:

With a complete mole, there is only abnormal placental tissue and no embryo.
With a partial mole, there is abnormal placental tissue and development of at least some embryonic tissue.

Molar pregnancy is uncommon, occurring in about one out of every 1,000 pregnancies in the United States. You are at increased risk of a molar pregnancy if you're older than age 40. The incidence is somewhat higher in people of East Asian descent.

Signs and symptoms of a molar pregnancy include:

Vaginal bleeding
Severe nausea and vomiting
Abdominal or pelvic cramps
High blood pressure

If you have these signs and symptoms, contact your doctor promptly. A doctor may make a diagnosis of molar pregnancy by an ultrasound exam.

Treatment involves removing the tumor from the uterus by dilation and curettage (D and C). In this procedure, the cervix is dilated and the tissues are removed by gentle suction. After the D and C, your doctor may monitor your levels of pregnancy hormone for up to a year to make sure that no molar tissue remains. The main concern is that molar pregnancy occasionally becomes cancerous.

Following a molar pregnancy, you should not try to become pregnant for at least a year. If you've had one molar pregnancy, you have a slightly increased risk of a second molar pregnancy. However, most women go on to have successful pregnancies.

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