Molar Pregnancy

What is Molar Pregnancy

Molar pregnancy (hydatidiform mole) is a mass of tissue that grows in the uterus after an egg is fertilized incorrectly. The mass does not develop into a fetus, and is considered an abnormal pregnancy.

Usually, the pregnancy ends on its own through miscarriage. In some cases, treatment may be required.

A molar pregnancy is the most common and most benign form of gestational trophoblastic disease and is characterized by proliferation of placental tissue after abnormal fertilization of an empty ovum by one (complete mole, no fetus) or two (partial mole, fetus present) sperm.

Patients characteristically present with markedly elevated serum β-hCG levels, an enlarged uterus, hyperemesis gravidarum, preeclampsia, vaginal bleeding, or a combination of these findings.

What are the causes?

This condition is caused by an egg that is fertilized incorrectly so that it has abnormal genetic material (chromosomes). This can result in one of two types of molar pregnancies:

  • Complete molar pregnancy. This is when all of the chromosomes in the fertilized egg are from the father, and none are from the mother.
  • Partial molar pregnancy. This is when the fertilized egg has chromosomes from the father and mother, but it has too many chromosomes.

What increases the risk?

Molar Pregnancy is more likely to develop in:

  • Women who are over the age of 35 or under the age of 20.
  • Women who have had a molar pregnancy in the past (very rare).

Other possible risk factors include:

  • Smoking more than 15 cigarettes a day.
  • History of infertility.
  • Having a blood type A, B, or AB.
  • Having a lack (deficiency) of vitamin A.
  • Using birth control pills (oral contraceptives).

What are the symptoms?

Symptoms of this condition include:

  • Vaginal bleeding.
  • Missed menstrual period.
  • The uterus growing faster than expected for a normal pregnancy.
  • Severe nausea and vomiting.
  • Severe pressure or pain in the uterus.
  • Abnormal ovarian cysts (theca lutein cysts).
  • Vaginal discharge that looks like grapes.
  • High blood pressure (early onset of preeclampsia).
  • Overactive thyroid gland (hyperthyroidism).
  • Not having enough red blood cells or hemoglobin (anemia).

How is this diagnosed?

This condition is diagnosed based on ultrasound and blood tests.

What is the ultrasound appearance of a molar pregnancy?

The edematous placental tissue and prominent chorionic villi of a molar pregnancy classically have a “snowstorm” appearance on US.

The endometrial canal is filled with hyperechoic placental tissue with good through-transmission and numerous small cystic villi, which may be too small to visualize.

A complete mole involves the entire placenta without a fetus. A partial mole involves a portion of the placenta and has an associated fetus, usually with multiple anomalies.

How is this treated?

Usually, molar pregnancies end on their own by miscarriage. A health care provider may manage this condition by:

  • Monitoring the levels of pregnancy hormones in your blood to make sure that the hormone levels are decreasing as expected.
  • Giving you a medicine called Rho (D) immune globulin. This medicine helps to prevent problems that may occur in future pregnancies as a result of a protein on red blood cells (Rh factor). You may be given this medicine if you do not have an Rh factor (you are Rh negative) and your sex partner has an Rh factor (he is Rh positive).
  • Putting you on chemotherapy. This involves taking medicines that regulate levels of pregnancy hormones. This may be done if your pregnancy hormone levels are not decreasing as expected.
  • Performing a procedure called dilation and curettage (D&C), or vacuum curettage. These are minor procedures that involve scraping or suctioning the molar pregnancy out of the uterus and removing it through the vagina. Even if a molar pregnancy ends on its own, one of these procedures may be done to make sure that all the abnormal tissue is out of the uterus.
  • Doing a surgical removal of the uterus (hysterectomy).

Follow these instructions at home:

  • Avoid getting pregnant for 6–12 months, or as long as told by your health care provider. To avoid getting pregnant, avoid having sex or use a reliable form of birth control every time you have sex.
  • Take over-the-counter and prescription medicines only as told by your health care provider.
  • Rest as needed, and slowly return to your normal activities.
  • Think about joining a support group. If you are struggling with grief, ask your health care provider for help.
  • Keep all follow-up visits as told by your health care provider. This is important. You may need follow-up blood tests or ultrasounds.

Contact a health care provider if:

  • You continue to have irregular vaginal bleeding.
  • You have abdominal pain.


  • A molar pregnancy (hydatidiform mole) is a mass of tissue that grows in the uterus after an egg is fertilized incorrectly.
  • This condition is more likely to develop in women who are over the age of 35 or under the age of 20 or women who have had a molar pregnancy in the past.
  • The most common symptom of this condition is vaginal bleeding.
  • Usually, molar pregnancy ends with a miscarriage, and no treatment is needed.

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