Partial Molar Pregnancy

A partial molar pregnancy is a type of molar pregnancy where the embryo (fertilized egg) has too many chromosomes. This happens when the egg gets 69 chromosomes instead of 46. In a molar pregnancy, the embryo either develops incompletely or doesn’t develop at all. Partial molar pregnancy is typically treated by removal of the embryo and placenta through a dilation and curettage (D&C) procedure.


What is a partial molar pregnancy?

A partial molar pregnancy is type of molar pregnancy, a pregnancy complication where a fertilized egg (embryo) doesn’t develop as it should. Molar pregnancies happen due to a genetic error during fertilization. Specifically, two sperm fertilize an egg instead of one. This results in too much genetic material for a pregnancy to continue correctly.

In a partial molar pregnancy, a fetus and placenta may start to develop. However, irregular tissue resembling fluid-filled sacs also develop. Since the placenta and fetus develop irregularly, the pregnancy can’t survive. In most cases, a partial molar pregnancy ends in miscarriage early in the pregnancy.

Molar pregnancies are a type of gestational trophoblastic disease. Gestational trophoblastic disease (GTD) is a group of conditions that cause tumors to grow inside a person’s uterus. Molar pregnancies are also called hydatidiform moles.

Partial molar pregnancies require immediate medical attention.

How rare is a partial molar pregnancy?

A partial molar pregnancy is less common than a complete molar pregnancy. However, less than 1% of all pregnancies — about 1 in 1,200 — are molar pregnancies.


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Symptoms and Causes

What are the symptoms of a partial molar pregnancy?

The most prominent symptom of a molar pregnancy is heavy bleeding from your vagina early in the pregnancy. The blood may be dark brown or bright red. Other symptoms of a partial molar pregnancy include:

  • Severe nausea and vomiting.
  • Pelvic pain.
  • Passing fluid-filled sacs from your vagina.
  • Hypertension (high blood pressure).

Other symptoms may include an overly large uterus or your uterus growing faster than usual in the first trimester of pregnancy.

What is the cause of a partial molar pregnancy?

A partial molar pregnancy is a genetic accident. In a normal pregnancy, the egg receives one set of 23 chromosomes from one parent and one set of 23 chromosomes from the other parent, for a total of 46 chromosomes. In a partial molar pregnancy, the egg receives two sets of chromosomes from the partner with a penis, usually because two sperm have fertilized one egg. The egg now has 69 chromosomes, instead of the normal 46.

What are the risk factors for a partial molar pregnancy?

Certain factors increase your risk of molar pregnancy. Partial molar pregnancies occur less frequently than complete molar pregnancies.

Risk factors include:

  • Having a prior molar pregnancy.
  • Being older than 40 or younger than 15.
  • Having two or more miscarriages.

Countries in Asia tend to have higher rates of molar pregnancy than the United States. In the U.S., white people are more likely to have a molar pregnancy than Black people.


What are the complications of a partial molar pregnancy?

Molar pregnancies have serious complications, including a rare form of cancer called choriocarcinoma.

One of the more common complications of molar pregnancy is persistent gestational trophoblastic neoplasia (GTN). This occurs when irregular tissue from a molar pregnancy continues to grow despite surgery to remove the molar pregnancy.

Other complications of a partial molar pregnancy are:

  • Severe bleeding.
  • High blood pressure.
  • Ovarian cysts.
  • Hyperthyroidism.

Generally, complete molar pregnancies have a higher risk of complications than a partial molar pregnancy.

How long do partial molar pregnancies last?

A partial molar pregnancy can’t survive. However, a pregnancy may continue for several weeks. Most will spontaneously end on their own in a miscarriage, with the grape-like clusters of tissue coming out of your vagina. However, some people don’t find out their pregnancy is a partial molar pregnancy until their first prenatal ultrasound.


Diagnosis and Tests

How is a partial molar pregnancy diagnosed?

Your healthcare provider diagnoses a partial molar pregnancy by performing an ultrasound. An ultrasound may show:

  • No fetus or a fetus that appears small.
  • A placenta that appears filled with cysts or looks unusual.

They’ll also order blood tests that measure the levels of human chorionic gonadotropin (HCG). HCG is a hormone that pregnant people produce. In a partial molar pregnancy, the HCG levels rise at a faster rate and often to a higher level than a normal pregnancy.

How early can a partial molar pregnancy be detected?

Most providers detect molar pregnancies in the first 12 weeks of pregnancy.

Management and Treatment

How is a partial molar pregnancy treated?

Your healthcare provider will treat a partial molar pregnancy by removing the fetus and placenta from your uterus. This is known as a dilation and curettage (D&C). Your provider may perform this procedure in the operating room when you’re asleep or in the office when you’re awake. You can ask your healthcare provider about these options.

After this procedure, your provider may continue to measure your HCG levels for up to one year to determine if there are any remnants of the molar tissue in your uterus. It’s important to use birth control during this time to keep from becoming pregnant.

In rare cases, molar tissue remains in your uterus after the D&C procedure. This tissue is gestational trophoblastic disease (GTD). Your healthcare provider will need to treat GTD with chemotherapy, radiation or a hysterectomy (surgery to remove the uterus and/or other reproductive organs).

Care at Cleveland Clinic


Can a partial molar pregnancy be prevented?

No, you can’t prevent a partial molar pregnancy (or a complete molar pregnancy).

If you’ve had a partial molar pregnancy before, talk to your healthcare provider about getting pregnant again. They may recommend waiting six months to one year. While the chances of having a molar pregnancy are low, you’re at higher risk for a repeat molar pregnancy if you’ve already had one.

Outlook / Prognosis

Can I become pregnant after a partial molar pregnancy?

Yes. The odds of having another molar pregnancy are small (approximately 1% to 2%), but there’s still a risk. You should discuss the timing of a future pregnancy with your healthcare provider, as they may recommend a certain time frame. Your uterus needs to be free of molar tissue and HCG levels will need to go back to regular levels.

Can a fetus survive a partial molar pregnancy?

No, a fetus won’t survive a partial molar pregnancy. At most, the pregnancy tissue may continue to develop for about 12 weeks (three months).

Living With

When should I see my healthcare provider?

If you’re pregnant, contact your healthcare provider if you notice any vaginal bleeding, nausea or pelvic pain. Symptoms of a molar pregnancy can resemble other conditions, so it’s important to contact a provider as soon as possible.

What questions should I ask my healthcare provider?

If you’ve had a partial molar pregnancy, it’s normal to have questions. Some questions you may ask your provider include:

  • When can I get pregnant again?
  • What are my chances of having a molar pregnancy again?
  • Am I at risk for serious complications?
  • Should I have additional testing?
  • Will I develop cancer from a molar pregnancy?

A note from Cleveland Clinic

Losing a pregnancy can be extremely hard, no matter what the circumstances. Allow yourself time to cope with the loss of your pregnancy and the diagnosis of a partial molar pregnancy. It’s important to attend all of your follow-up appointments after a partial molar pregnancy. Your healthcare provider will discuss future pregnancies with you. Remember, your chances of having a second molar pregnancy are low and most people go on to have successful pregnancies.

Medically Reviewed

Last reviewed on 04/11/2023.

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