A hydatidiform mole is a rare mass or growth that forms inside the uterus at the beginning of a pregnancy. It is a type of gestational trophoblastic disease (GTD).

See also:

• Gestational trophoblastic disease
• Choriocarcinoma (a cancerous form of GTD)

A hydatidiform mole, or molar pregnancy, results from over-production of the tissue that is supposed to develop into the placenta. The placenta normally feeds a fetus during pregnancy. In this condition, the tissues develop into an abnormal growth, called a mass.

There are two types:

• Partial molar pregnancy
• Complete molar pregnancy

A partial molar pregnancy means there is an abnormal placenta and some fetal development.

In a complete molar pregnancy, there is an abnormal placenta but no fetus.

Both forms are due to problems during fertilization. Potential causes may include defects in the egg, problems within the uterus, or a diet low in protein, animal fat, and vitamin A. Women under age 16 or older than 40 have a higher risk for this condition. You also are more likely to have a molar pregnancy if you have had one in the past.

• Abnormal growth of the womb (uterus)
  • Excessive growth in about half of cases
  • Smaller-than-expected growth in about a third of cases
• Nausea and vomiting that may be severe enough to require a hospital stay
• Vaginal bleeding in pregnancy during the first 3 months of pregnancy
• Symptoms of hyperthyroidism
  • Heat intolerance
  • Loose stools
  • Rapid heart rate
  • Restlessness, nervousness
  • Skin warmer and more moist than usual
  • Trembling hands
  • Unexplained weight loss
• Symptoms similar to preeclampsia that occur in the 1st trimester or early 2nd trimester -- this is almost always a sign of a hydatidiform mole, because preeclampsia is extremely rare this early in a normal pregnancy
  • High blood pressure
  • Swelling in feet, ankles, legs

A pelvic examination may show signs similar to a normal pregnancy, but the size of the womb may be abnormal and the baby's heart sounds are absent. There may be some vaginal bleeding.

A pregnancy ultrasound will show an abnormal placenta with or without some development of a baby.

Tests may include:

• HCG blood test
• Chest x-ray
• CT or MRI of the abdomen

If your doctor suspects a molar pregnancy, a suction curettage (D and C) may be performed.

A hysterectomy may be an option for older women who do not wish to become pregnant in the future.

After treatment, serum HCG levels will be followed.

More than 80% of hydatidiform moles are benign (noncancerous). The outcome after treatment is usually excellent. Close follow-up is essential. After treatment, you should use very effective contraception for at least 6 to 12 months to avoid pregnancy.

In some cases, hydatidiform moles may develop into invasive moles. These moles may grow so far into the uterine wall and cause bleeding or other complications.

In a few cases, a hydatidiform mole may develop into a choriocarcinoma, a fast-growing cancerous form of gestational trophoblastic disease. See: Choriocarcinoma

Lung problems may occur after a D and C if the woman's uterus is bigger than 16 weeks gestational size.

Kavanagh JJ, Gershenson DM. Gestational trophoblastic disease: hydatidiform mole, nonmetastatic and metastatic gestational trophoblastic tumor: diagnosis and management. In: Katz VL, Lentz GM, Lobo RA, Gershenson DM, eds. Comprehensive Gynecology. 5th ed. Philadelphia, Pa: Mosby Elsevier; 2007:chap 35.

Copeland LJ, Landon MB. Malignant diseases and pregnancy. In: Gabbe SG, Niebyl JR, Simpson JL, eds. Obstetrics - Normal and Problem Pregnancies. 5th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2007:chap 45.

Soper J, Creasman WT. Gestational trophoblastic disease. In: DiSaia P, Creasman W, eds. Clinical Gynecologic Oncology. 7th ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 7.