Molar pregnancy (Hydatidiform mole)
What is Molar pregnancy (Hydatidiform mole)?
A molar pregnancy happens when an egg and sperm combine incorrectly during fertilization. Instead of a normal embryo developing, abnormal tissue grows inside the uterus. This tissue is called a hydatidiform mole and forms from cells that would normally become the placenta.
There are two types of molar pregnancy. A complete molar pregnancy contains no fetal tissue at all, just abnormal placental cells. A partial molar pregnancy may contain some fetal tissue, but it cannot develop into a viable baby. Both types produce abnormally high levels of pregnancy hormone and require medical treatment.
Molar pregnancies occur in about 1 in every 1,000 pregnancies in the United States. While rare, they need prompt diagnosis and treatment. Most women recover fully after treatment, though monitoring is essential to ensure all abnormal tissue is removed.
Symptoms
- Vaginal bleeding during the first trimester, often dark brown like prunes
- Severe nausea and vomiting, worse than typical morning sickness
- Uterus that measures larger than expected for gestational age
- High blood pressure early in pregnancy, before 20 weeks
- Pelvic pressure or pain
- Passing grape-like tissue clusters from the vagina
- Signs of hyperthyroidism such as tremors or rapid heartbeat
- Swelling in the hands and feet earlier than usual
Some women discover a molar pregnancy during a routine ultrasound before symptoms appear. Early pregnancy bleeding is the most common symptom that leads to diagnosis.
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Causes and risk factors
Molar pregnancies happen due to errors during fertilization. In a complete molar pregnancy, an egg with no genetic material is fertilized by one or two sperm. The resulting cells contain only paternal DNA and grow abnormally. In a partial molar pregnancy, a normal egg is fertilized by two sperm, creating too many chromosomes. This leads to abnormal development of both placental tissue and some fetal tissue.
Risk factors include maternal age over 35 or under 20, history of previous molar pregnancy, and certain dietary deficiencies. Women who have had one molar pregnancy have a 1 to 2 percent chance of having another. Asian women and those with low levels of vitamin A and carotene may face slightly higher risk. Most cases occur randomly without clear preventable causes.
How it's diagnosed
Doctors diagnose molar pregnancy through a combination of ultrasound imaging and blood tests. An ultrasound typically shows a characteristic snowstorm pattern instead of a developing fetus. Blood tests measure human chorionic gonadotropin, or hCG, the hormone produced during pregnancy. In molar pregnancies, hCG levels are unusually high, often exceeding 100,000 mIU/mL.
Rite Aid offers hCG testing as an add-on to our health panel at Quest Diagnostics locations. After diagnosis and treatment, regular hCG monitoring is critical to ensure levels return to normal. Persistent high levels may signal that abnormal tissue remains and requires additional treatment. Your doctor will typically check hCG weekly until levels reach zero, then monthly for six months to a year.
Treatment options
- Dilation and curettage, or D&C, to remove abnormal tissue from the uterus
- Sometimes suction evacuation under anesthesia is performed
- In rare cases, hysterectomy if the patient does not wish to preserve fertility
- Regular hCG blood test monitoring for 6 to 12 months after removal
- Avoiding pregnancy for 6 to 12 months while being monitored
- Chemotherapy if abnormal tissue persists or spreads
- Treatment for complications like high blood pressure or thyroid problems
- Emotional support and counseling to process pregnancy loss
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Frequently asked questions
A molar pregnancy results from an error during fertilization when genetic material combines incorrectly. In complete molar pregnancies, an empty egg is fertilized by sperm, leaving only paternal DNA. In partial molar pregnancies, one egg is fertilized by two sperm. Most cases occur randomly and are not caused by anything the mother did or did not do.
Molar pregnancies occur in about 1 in every 1,000 pregnancies in the United States. They are more common in women over 35 or under 20 years old. Asian women may have slightly higher rates. Women who have had one molar pregnancy have a 1 to 2 percent chance of having another.
The most common symptom is vaginal bleeding during the first trimester, often dark brown in color. Other signs include severe nausea, a uterus larger than expected, and high blood pressure before 20 weeks. Some women pass grape-like tissue clusters. Many molar pregnancies are discovered during routine ultrasounds before symptoms appear.
Doctors use ultrasound and blood tests to diagnose molar pregnancy. The ultrasound shows a characteristic pattern instead of a developing fetus. Blood tests measure hCG levels, which are abnormally high in molar pregnancies, often over 100,000 mIU/mL. These tests together confirm the diagnosis and rule out normal pregnancy.
No, a molar pregnancy cannot develop into a normal, viable pregnancy. The abnormal fertilization creates tissue that cannot form a healthy baby. Complete molar pregnancies contain no fetal tissue at all. Partial molar pregnancies may have some fetal tissue, but it cannot survive. Treatment is necessary to remove all abnormal tissue.
Treatment involves removing the abnormal tissue through a procedure called dilation and curettage, or D&C. After removal, doctors monitor hCG levels regularly for 6 to 12 months. If tissue persists or spreads, chemotherapy may be needed. Women are advised to avoid pregnancy during the monitoring period to ensure complete recovery.
Yes, most women can have successful pregnancies after a molar pregnancy. Doctors recommend waiting 6 to 12 months after hCG levels return to normal before trying to conceive. This waiting period ensures all abnormal tissue is gone and reduces complications. About 98 to 99 percent of women have no recurrence in future pregnancies.
Gestational trophoblastic disease, or GTD, is a group of rare tumors that form from pregnancy tissue. Molar pregnancy is one type of GTD. In some cases, abnormal tissue persists after a molar pregnancy is removed, requiring chemotherapy. With proper treatment, the cure rate for GTD exceeds 90 percent, even when it spreads.
After molar pregnancy removal, you will need weekly hCG blood tests until levels reach zero. Once levels are normal, testing continues monthly for 6 to 12 months. This monitoring detects any persistent abnormal tissue early. If levels plateau or rise, additional treatment may be needed.
Most women recover completely with no long-term health problems. About 15 to 20 percent develop persistent gestational trophoblastic disease requiring chemotherapy. There is a small increased risk of having another molar pregnancy in the future. With proper monitoring and treatment, fertility and future pregnancy outcomes are generally excellent.