Hydatidiform mole is a rare mass or growth that forms inside the womb (uterus) at the beginning of a pregnancy. It is a type  gestational trophoblastic disease (GTD). A cancerous form of GTD is called choriocarcinoma. A.D.A.M.

Causes, incidence, and risk factors

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

There are two types:

• Partial molar pregnancy: There is an abnormal placenta and some fetal development.
• Complete molar pregnancy: There is an abnormal placenta but no fetus.

Both forms are due to problems during fertilization. The exact cause of fertilization problems is unknown. A diet low in protein, animal fat, and vitamin A may play a role.

Symptoms

• 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

Signs and tests

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
• Complete blood count
• Blood clotting tests
• Kidney and liver function tests

Treatment

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 level will be followed. It is important to avoid pregnancy and to use a reliable contraceptive for 6 - 12 months after treatment for a molar pregnancy. This allows for accurate testing to be sure that the abnormal tissue does not grow back. Women who get pregnant too soon after a molar pregnancy have a high risk of having another molar pregnancy.

Expectations (prognosis)

More than 80% of hydatidiform moles are benign (noncancerous). Treatment is usually successful. Close follow-up by your doctor is important. After treatment, use effective contraception for at least 6 - 12 months to avoid pregnancy.

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

In a few cases, a hydatidiform mole develops into a choriocarcinoma. This is a fast-growing cancerous form of gestational trophoblastic disease. 

Complications

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

Complications of molar pregnancy include:

• Preeclampsia
• Thyroid problems
• Molar pregnancy that continues or comes back

Complications related to the surgery to remove a molar pregnancy include:

• Excessive bleeding
• Side effects of anesthesia

References

1. Copeland LJ, Landon MB. Malignant diseases and pregnancy. In: Gabbe SG, Niebyl JR, Simpson JL, eds. Obstetrics - Normal and Problem Pregnancies. 6th ed. Philadelphia, PA: Elsevier Saunders; 2012:chap 47.
2. Goldstein DP, Berkowitz RS. Gestational trophoblastic disease. In: Abeloff MD, Armitage JO, Niederhuber JE, Kastan MB, McKenna WG, eds. Abeloff’s Clinical Oncology. 4th ed. Philadelphia, PA: Elsevier Churchill Livingstone; 2008:chap 94.
3. 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. 6th ed. Philadelphia, PA: Elsevier Mosby; 2012:chap 35.

Review Date: 11/8/2012.

Reviewed by: Susan Storck, MD, FACOG, Chief, Eastside Department of Obstetrics and Gynecology, Group Health Cooperative of Puget Sound, Bellevue, Washington; Clinical Teaching Faculty, Department of Obstetrics and Gynecology, University of Washington School of Medicine. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, David R. Eltz, Stephanie Slon, and Nissi Wang.