Hydatidiform mole is a rare mass or growth that forms inside the womb (uterus) at the beginning of a pregnancy. It is a type of gestational trophoblastic disease (GTD).
Hydatidiform mole, or molar pregnancy, results from too much 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 2 types of these masses:
- Partial molar pregnancy. There is an abnormal placenta and some fetal development.
- Complete molar pregnancy. There is an abnormal placenta and no fetus.
Both forms are due to problems during fertilization. The exact cause of fertilization problems is unknown.
There are no known ways to prevent these masses from forming.
Symptoms of a molar pregnancy are:
- Abnormal growth of the uterus, either bigger or smaller than usual
- Nausea and vomiting that may be severe enough to require a hospital stay
- Vaginal bleeding during the first 3 months of pregnancy
- Symptoms of hyperthyroidism, including heat intolerance,loose stools, rapid heart rate, restlessnessor nervousness, warm and moist skin, trembling hands, or unexplained weight loss
- Symptoms similar to preeclampsia that occur in the first trimester or early second trimester, including high blood pressure and swelling in the feet, ankles, and legs (this is almost always a sign of a hydatidiform mole, because preeclampsia is extremely rare this early in a normal pregnancy)
Exams and Tests
A pelvic exam may show signs similar to a normal pregnancy. But the size of the womb may be abnormal and there may be no heart sounds from the baby. 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 (quantitative levels) blood test
- Chest x-ray
- CT or MRI of the abdomen (imaging tests)
- Complete blood count (CBC)
- Blood clotting tests
- Kidney and liver function tests
If your health care provider suspects a molar pregnancy, a dilation and curettage (D and C) will most likely be recommended.
Sometimes a partial molar pregnancy can continue. A woman may choose to continue her pregnancy in the hope of having a successful birth and delivery. However, these are very high-risk pregnancies. Risks include bleeding, problems with blood pressure, and premature delivery (having the baby before it is fully developed). Also, the condition may become worse. Women need to thoroughly discuss the risks with their health care provider before continuing the pregnancy.
A hysterectomy (surgery to remove the uterus) may be an option for older women who do not wish to become pregnant in the future.
After treatment, your hCG level will be followed. It is important to avoid another pregnancy and to use a reliable contraceptive for 6 to 12 months after treatment for a molar pregnancy. This time 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 are at high risk of having another molar pregnancy.
Most hydatidiform moles are noncancerous (benign). Treatment is usually successful. Close follow-up by your health care provider is important to ensure that signs of the molar pregnancy are gone and pregnancy hormone levels return to normal.
Sometimes hydatidiform moles can continue and start changing into cancer. These moles can grow deep into the uterine wall and cause bleeding or other complications.
Rarely, a hydatidiform mole develops into a choriocarcinoma. This is a fast-growing cancer. It is usually treated with chemotherapy, and can be life-threatening.
Complications of molar pregnancy include:
- Change to invasive molar disease or choriocarcinoma
- Thyroid problems
- Molar pregnancy that continues or comes back
Complications from surgery to remove a molar pregnancy include:
- Excessive bleeding, possibly requiring a blood transfusion
- Side effects of anesthesia
Hydatid mole; Molar pregnancy
American College of Obstetricians and Gynecologists. Clinical management guidelines of obstetrician-gynecologists. Diagnosis and treatment of gestational trophoblastic disease. Obstet Gynecol. 2004;103:1365. Practice Bulletin No. 53.
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.
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.
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 11/14/2014
Updated by: Cynthia D. White, MD, Fellow American College of Obstetricians and Gynecologists, Group Health Cooperative, Bellevue, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.