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Molar Pregnancy

Reviewed by James Brann, M.D.

Gestational Trophoblastic Disease (GTD)

Learn about a molar pregnancy.

Gestational trophoblastic disease (GTD) is a group of tumors that arise from the cells of the placenta. All forms of the GTD tumor group produce the pregnancy hormone (Beta hCG).

The hydatidiform mole (molar pregnancy) makes up 90 percent of the Gestational trophoblastic disease cases. They are non-cancerous tumors that result from an abnormal fertilization of the egg by the sperm. The incidence of the hydatidiform mole pregnancy is very rare, it occurs in 1 per 1,000 pregnancies.

The other 10 percent of gestational trophoblastic disease cases represent malignant or cancerous tumors because of their potential for local tissue invasion and metastases to distant organs.

The two main risk factors for developing a pregnancy complicated by GTD are maternal age (over age 35 years) and a history of a previous pregnancy complicated by GTD.

Symptoms of GTD include:

  • Vaginal bleeding early in pregnancy

  • Enlarged uterus that is bigger than expected for gestational age

  • Pelvic pain beyond the normal early pregnancy discomfort

  • Ultrasound shows ovarian cysts called “Theca lutein cysts”

  • Your blood count is lower than what is expected in pregnancy

  • Sever morning sickness

  • Vaginal passage of tissue that looks like grapes “hydropic vesicles”

Since the above symptoms are also seen in pregnancy, plus GTD can produce the pregnancy hormone, GTD is often misdiagnosed as a pregnancy. This is due to fact that most women with this disorder have missed a period, have a positive pregnancy test and demonstrate other signs of pregnancy. Most doctors initially suspect a pregnancy complication such as a miscarriage or ectopic pregnancy instead of GTD.

The hydatidiform mole (molar pregnancy) has two forms:

  • A complete hydatidiform mole results when an empty egg (no chromosomes) is fertilized by two sperm. The complete mole does not have a fetus, the uterine size is greater than expected for gestational age and a higher than normal pregnancy hormone (beta hCG) is found. Vaginal bleeding is common and often confused with the bleeding from a miscarriage.

  • A partial hydatidiform mole results when an egg with half the number of chromosomes is fertilized by two sperm. The partial hydatidiform mole is associated with a fetus and frequently misdiagnosed as a miscarriage. The correct diagnosis is only made after the tissue is reviewed by the pathologist.

Since a malignant disease (invasive mole or choriocarcinoma) can develop from a hydatidiform mole you should not become pregnant until your pregnancy test is again negative. The use of birth control is very important at this time.

According to FIGO criteria, the presence of a malignancy (invasive mole or choriocarcinoma) after evacuation of a hydatidiform molar pregnancy should be suspected if any of the following is present:

  • A hCG level that plateaus and does not decline more than 10 percent when tested four times over a three week period.

  • A hCG level that rises more than 10 percent when tested three times in two weeks.

  • A persistent detectable hCG level over six months.
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