Merck Manual

Please confirm that you are not located inside the Russian Federation

honeypot link

Molar Pregnancy

(Gestational Trophoblastic Disease; Hydatidiform Mole)


Pedro T. Ramirez

, MD, Houston Methodist Hospital;

Gloria Salvo

, MD, MD Anderson Cancer Center

Reviewed/Revised Oct 2023

A molar pregnancy (hydatidiform mole) and other types of gestational trophoblastic disease are growth of an abnormal fertilized egg or an overgrowth of tissue from the placenta.

  • Women with a molar pregnancy appear to be pregnant, but the uterus enlarges much more rapidly than in a normal pregnancy.

  • Most women have severe nausea and vomiting and vaginal bleeding, and some have very high blood pressure.

  • Ultrasonography and blood tests to measure human chorionic gonadotropin (which is produced early during pregnancy) are done.

  • Molar pregnancies are treated using dilation and curettage (D and C).

  • If the disorder persists, chemotherapy is needed.

Most often, a molar pregnancy is an abnormal fertilized egg that develops into a hydatidiform mole rather than a fetus. A molar pregnancy may also develop from cells that remain in the uterus after a miscarriage Miscarriage A miscarriage is a pregnancy loss before 20 weeks of pregnancy. Miscarriages are very common, especially early in pregnancy. Most of the time, the cause of a miscarriage is unknown, but it may... read more , a full-term pregnancy, or a mislocated pregnancy (ectopic pregnancy Ectopic Pregnancy Ectopic pregnancy is attachment (implantation) of a fertilized egg in an abnormal location, such as a fallopian tube. In an ectopic pregnancy, the fetus cannot survive. Women with an ectopic... read more ). Rarely, a molar pregnancy develops when there is a living fetus. In such cases, the fetus typically dies, and a miscarriage often occurs.

Molar pregnancies are most common among women under 17 or over 35 years old. In the United States, they occur in approximately 1 in 2,000 pregnancies.

Molar pregnancies are a type of gestational trophoblastic disease.

Did You Know...

  • An abnormal fertilized egg or abnormal placental tissue can overgrow, causing symptoms similar to those of pregnancy, but the abdomen becomes larger more rapidly.

Types of gestational trophoblastic disease

Gestational trophoblastic disease is a group of disorders that develop from cells (called trophoblasts) that surround a developing embryo Development of the Embryo A baby goes through several stages of development, beginning as a fertilized egg. The egg develops into a blastocyst, an embryo, then a fetus. During each normal menstrual cycle, one egg (ovum)... read more Development of the Embryo and that eventually form the placenta and amniotic sac. The affected cells grow abnormally and multiply quickly.

Gestational trophoblastic disease includes

  • Noncancerous tumors that may become cancerous: These tumors include hydatidiform mole, exaggerated placental site, and placental site nodule.

  • Cancerous tumors located in the placenta: These tumors (called gestational trophoblastic neoplasia) include placental-site trophoblastic tumor, epithelioid trophoblastic tumor, choriocarcinoma, and invasive mole.

Approximately 80% of cases of gestational trophoblastic disease are not cancerous.

The rest tend to persist and start to invade surrounding tissue. Approximately 2 to 3% of hydatidiform moles develop into choriocarcinomas. Choriocarcinomas can spread quickly through the lymphatic vessels or bloodstream.

Placental-site trophoblastic tumors and epithelioid trophoblastic tumors are very rare.

Symptoms of Molar Pregnancy

Women who have a molar pregnancy (hydatidiform mole) feel as if they are pregnant. But because molar pregnancies grow much faster than a fetus, the abdomen becomes larger much faster than it does in a normal pregnancy. Severe nausea and vomiting and vaginal bleeding are common. As parts of the mole deteriorate, small amounts of tissue, which resemble a bunch of grapes, may pass through the vagina. These symptoms indicate the need for prompt evaluation by a doctor.

Molar pregnancies can cause serious complications, including the following:

If choriocarcinoma develops, women may have other symptoms, caused by spread (metastasis) to other parts of the body.

An overactive thyroid gland (hyperthyroidism Hyperthyroidism Hyperthyroidism is overactivity of the thyroid gland that leads to high levels of thyroid hormones and speeding up of vital body functions. Graves disease is the most common cause of hyperthyroidism... read more Hyperthyroidism ) can occur in women with gestational trophoblastic disease. Symptoms can include an abnormally fast heart rate (tachycardia), warm skin, sweating, heat intolerance, and mild tremors.

Diagnosis of Molar Pregnancy

  • Blood tests

  • Ultrasonography

Often, doctors can diagnose a molar pregnancy (hydatidiform mole) shortly after it forms. They suspect a molar pregnancy based on symptoms, such as a uterus that is much larger than expected and a vaginal discharge of grapelike tissue.

A pregnancy test is done. If women have a molar pregnancy, results are positive, but no fetal movement and no fetal heartbeat are detected.

Blood tests to measure the level of human chorionic gonadotropin (hCG—a hormone normally produced early in pregnancy) are done. If a molar pregnancy or another type of gestational trophoblastic disease is present, the level is usually very high because these tumors produce a large amount of this hormone.

If the level of hCG is very high, doctors do blood tests to check thyroid function and determine whether hyperthyroidism is present.

Ultrasonography is done to be sure that the growth is a hydatidiform mole and not a fetus or amniotic sac (which contains the fetus and fluid around it).

A sample of tissue is removed during dilation and curettage Dilation and Curettage Sometimes doctors recommend screening tests, which are tests that are done to look for disorders in people who have no symptoms. If women have symptoms related to the reproductive system (gynecologic... read more Dilation and Curettage (D and C) or obtained when tissue is passed and is then examined under a microscope (biopsy) to confirm the diagnosis. Abnormal tissue may be removed during D and C.

If gestational trophoblastic disease is diagnosed, staging tests are done to find out if the tumor has spread from where it started to other parts of the body. Tests include computed tomography (CT) of the chest, abdomen, and pelvic area. Magnetic resonance imaging (MRI) may also be done.


Doctors stage gestational trophoblastic neoplasia (the form of gestational trophoblastic disease that is usually cancerous) based on how far it has spread:

  • Stage I: The tumor is only in the body of the uterus (not in the cervix—the lower part of the uterus).

  • Stage II: The tumor has spread outside the uterus to the ovary, fallopian tube, vagina, and/or nearby tissues.

  • Stage III: The tumor has spread to the lungs.

  • Stage IV: The tumor has spread to more distant sites, such as the brain, liver, kidneys, and/or digestive tract.

Treatment of Molar Pregnancy

  • Removal of the molar pregnancy

  • Tests to check for recurrence and/or spread

  • If needed, chemotherapy

Usually, any type of gestational trophoblastic disease can be successfully diagnosed and treated, without endangering reproductive function.

A molar pregnancy (hydatidiform mole) or any type of gestational trophoblastic neoplasia is completely removed, usually by D and C with suction. Removal of the uterus (hysterectomy Treatment Ovarian cancer is cancer of the ovaries. It is related to fallopian tube cancer, which develops in the tubes that lead from the ovaries to the uterus, and peritoneal cancer, which is cancer... read more ) is rarely necessary but may be done if women do not plan to have children.

Tests are done to determine whether women need additional treatment after the mole is removed.

A chest x-ray is taken to see whether the molar pregnancy tissue has spread to the lungs.

The level of human chorionic gonadotropin in the blood is measured to determine whether the molar pregnancy was completely removed. When removal is complete, the level returns to normal, usually within 10 weeks, and remains normal, and no further treatment is needed. While hCG is being measured, women should use effective contraception because pregnancy makes interpreting hCG measurement difficult. If the level does not return to normal, the disease is considered persistent. Then, computed tomography (CT) of the brain, chest, abdomen, and pelvis is done to determine whether choriocarcinoma has developed and spread.

Chemotherapy is needed if the molar pregnancy tissue persists or has spread. If the molar pregnancy is considered low risk, chemotherapy may consist of only one chemotherapy drug. If this treatment is ineffective, a combination of chemotherapy drugs may be used, or hysterectomy may be done.

If the molar pregnancy tissue has spread widely and is considered high risk, doctors refer women to a specialist.

After a hysterectomy, if done, chemotherapy is given and hCG levels are monitored to make sure the disease has been successfully treated.

When gestational trophoblastic disease is diagnosed, doctors talk to women about their desire to be able to have children. If chemotherapy, which may damage the ovaries, is needed, sometimes steps can be taken to preserve fertility, such as freezing eggs before chemotherapy is given. Even if hysterectomy is done, the ovaries do not need to be removed to treat molar pregnancy.

Women who have had a molar pregnancy removed are advised not to become pregnant for 12 months. Oral contraceptives Oral Contraceptives Contraceptive hormones can be Taken by mouth (oral contraceptives) Inserted into the vagina (vaginal rings) Applied to the skin (patch) Implanted under the skin read more Oral Contraceptives are frequently recommended, but other effective contraceptive methods can be used. Pregnancy is delayed so that doctors can make sure that treatment was successful.

If women who have had a molar pregnancy become pregnant, doctors do ultrasonography early in the pregnancy to determine whether the pregnancy is normal. After the baby is delivered, doctors usually send the placenta to a laboratory to be checked for abnormalities.

Prognosis for Molar Pregnancy

With treatment, many women are cured. The likelihood of cure depends on whether the molar pregnancy tissue has spread and other factors:

  • If the molar pregnancy tissue has not spread: Virtually 100%

  • If the molar pregnancy tissue has spread but is considered low risk: 90 to 95%

  • If the choriocarcinoma has spread widely and is considered high risk: 60 to 80%

Most women who have had a molar pregnancy can have children afterward and do not have a higher risk of a miscarriage, complications during pregnancy, or children with birth defects.

Approximately 1 to 2% of women who have had a molar pregnancy have another one. So if women have had a molar pregnancy, ultrasonography is done early in subsequent pregnancies. If women have consecutive molar pregnancies, genetic testing is done.

More Information

The following English-language resource may be useful. Please note that THE MANUAL is not responsible for the content of this resource.

quiz link

Test your knowledge

Take a Quiz!