Molar pregnancy

A molar pregnancy (also called hydatidiform mole) is a rare pregnancy complication. It happens when abnormal tissue grows inside the uterus instead of a normal fetus. This tissue comes from cells that would normally become the placenta.

A molar pregnancy is a type of gestational trophoblastic disease. It occurs when there are problems with the genetic material during fertilization. Instead of a normal pregnancy developing, abnormal tissue grows rapidly inside the uterus. This tissue looks like small grape-like clusters.

There are two main types of molar pregnancy:

In a complete molar pregnancy, there is no normal fetus or amniotic sac. This happens when:

• An egg with no genetic material gets fertilized by one or two sperm
• The result is tissue with only the father's genetic material
• All the chromosomes come from the father
• Under ultrasound, it looks like a "snowstorm" pattern
• This type has a higher risk of becoming cancerous

In a partial molar pregnancy:

• There may be some fetal tissue, but it cannot develop normally
• This happens when a normal egg is fertilized by two sperm
• The fetus has too many chromosomes (69 instead of the normal 46)
• The fetus cannot survive and is usually lost early in pregnancy
• There may be some normal placental tissue mixed with abnormal tissue

Early signs of a molar pregnancy are similar to normal pregnancy, but may include:

• Vaginal bleeding during the first 3 months of pregnancy
• Severe nausea and vomiting (worse than normal pregnancy)
• A uterus that grows faster and larger than expected
• Very high levels of hCG hormone in blood tests
• High blood pressure early in pregnancy
• Ovarian cysts caused by high hormone levels
• No fetal heartbeat heard on ultrasound
• Passing grape-like tissue from the vagina

Some women may have no symptoms at first.

Doctors use several tests to diagnose molar pregnancy:

• Ultrasound examination - Shows the characteristic "snowstorm" pattern
• Blood tests - Measure very high hCG hormone levels
• Physical examination - Check uterus size and other symptoms
• Tissue examination - If grape-like tissue is passed, it can be tested

Early diagnosis is important for proper treatment and to prevent complications.

Treatment for molar pregnancy includes:

• Suction curettage - A surgical procedure to remove all abnormal tissue from the uterus
• This is usually done under anesthesia in a hospital
• The removed tissue is examined under a microscope

After treatment, doctors closely monitor patients because:

• hCG hormone levels must return to zero
• Blood tests are done weekly, then monthly for up to one year
• Chest X-rays may be done to check for spread to lungs
• Patients should not get pregnant for at least 6 months to 1 year
• Birth control is strongly recommended during this time

Molar pregnancy can lead to serious complications:

• Heavy bleeding
• High blood pressure
• Anemia from blood loss
• Thyroid problems

• Persistent gestational trophoblastic disease - When abnormal cells remain after treatment
• Choriocarcinoma - A rare but serious type of cancer that can develop
• Cancer can spread to other parts of the body including:
  • Lungs
  • Liver
  • Brain
  • Other organs

This is why long-term follow-up care is very important.

Some factors that may increase risk include:

• Age under 20 or over 35 years
• Previous molar pregnancy
• Certain ethnic backgrounds
• Diet low in vitamin A and protein

• Most molar pregnancies are cured with proper treatment
• About 90% of patients have no further problems
• Future normal pregnancies are usually possible
• Early detection and treatment give the best results

See a doctor right away if you have:

• Heavy vaginal bleeding during pregnancy
• Severe nausea and vomiting
• Passage of grape-like tissue
• No fetal movement when expected
• Very rapid uterus growth

1. Molar Pregnancy: Early Diagnosis, Clinical Management, and the Central Role of Referral Centers. PMC12346673. 2025. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC12346673/ 2. Diagnosis and Surgical Treatment of Hydatidiform Mole. PMC12386084. 2025. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC12386084/ 3. Hydatidiform Mole - StatPearls. NCBI Bookshelf. 2024. Available at: https://www.ncbi.nlm.nih.gov/books/NBK459155/ 4. Advances in the diagnosis and early management of gestational trophoblastic disease. PMC9978730. 2022. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC9978730/