Molar Pregnancy

There are two types:

• Complete molar pregnancies do not have any fetal tissue at all. Complete moles can not develop into a baby.
• Partial molar pregnancies do have some fetal tissue, but it is almost always very abnormal.

About 1 in every 1,000 pregnancies turns out to be a molar pregnancy.

How These Pregnancies Happen

Just like normal pregnancies, these pregnancies begin with sperm fertilizing an egg. Normally, the sperm has one set of chromosomes (genes) from the father, and the egg has one set from the mother. It takes both sets of chromosomes for a baby to develop. But occasionally, an egg forms that does not contain any chromosomes at all. If a sperm fertilizes one of these “empty” eggs, the result is a complete hydatidiform mole.

Partial moles are formed when a normal egg is fertilized by two sperm at once. In that case, the egg winds up with three sets of chromosomes: one from the mother and two from the father. A baby can not develop normally with an extra set of chromosomes.

Who Is at Risk?

Molar pregnancies are not common, but they can happen to anyone. Some risk factors have been identified, but even with these risk factors the chance of having a molar pregnancy is still very low.

Risk factors include:

• Age. Women over 40 and under 20 are at highest risk for complete molar pregnancies.
• Prior molar pregnancy. Research suggests 98% of pregnancies in women who had prior molar pregnancies are normal.
• Blood type. There is a slightly higher risk in women with blood type A or AB.
• Use of birth control pills.
• A high number of sexual partners (more than 10).
• Low socioeconomic status.
• Poor nutrition.

Symptoms

• Vaginal bleeding. This occurs in 97% of molar pregnancies. There may be blood clots, brownish discharge, or tissue that looks like a bunch of grapes.
• A uterus that is larger or smaller than it should be at that point in the pregnancy.
• Morning sickness that is more severe than normal.
• Rapid heartbeat, tremors, heat intolerance, restlessness, weight loss, and/or loose stools, caused by hyperthyroidism. Hyperthyroidism occurs in about 7% of cases.
• Preeclampsia symptoms of high blood pressure, protein in the urine, and swelling in the feet and/or legs during the first or second trimester. In normal pregnancy, if preeclampsia happens, it’s usually during the third trimester.

Diagnosis

Molar pregnancies are most often diagnosed after an incomplete miscarriage. In an incomplete miscarriage, the pregnancy has ended but the uterus must be scraped to remove the products of conception. At that point, the doctor may discover abnormal molar tissue.

If a woman is having signs or symptoms, her doctor will probably do a pelvic exam to check for abnormalities. A blood test for human chorionic gonadotropin (HCG), a hormone that appears during pregnancy, will usually be abnormal. An ultrasound may also show the molar pregnancy.

Treatment

The initial treatmen is to remove the pregnancy tissue. This is done by a procedure called dilation and curettage, or D&C. The doctor uses a suction device and a scraping tool to remove the tissue from the uterus, entering through the vagina.

After the molar pregnancy is removed, the doctor will probably want to monitor levels of HCG. It should decline to unmeasurable levels within three months. If it does not, there may be molar tissue remaining, and a major concern is that it could become cancerous. It’s important for the woman not to become pregnant again during that time, because pregnancy raises HCG levels.

Invasive Moles and Choriocarcinoma

Most of the time, after the D&C, the HCG will return to normal and nothing else needs to be done. In about 10% of molar pregnancies, the molar tissue invades the wall of the uterus. This may cause bleeding or other complications.

In about 1 to 3% of cases, molar tissue becomes cancerous and can spread to other parts of the body. The resulting tumor is called a choriocarcinoma. It is more common with complete moles than with partial moles.

Treatment for Invasive Moles and Choriocarcinoma

Possible treatments for invasive moles or choriocarcinoma include:

• Chemotherapy
• Hysterectomy, particularly if a woman does not want to have any more children
• Radiation therapy, if chemotherapy has failed and the cancer has spread to other parts of the body

If there are no complications, choriocarcinoma can almost always be cured.

Additional Resources

• March of Dimes
• National Institutes of Health
• Information on GTD and Choriocarcinoma from the American Cancer Society