What Is a Molar Pregnancy?

Medically Reviewed By Stacy A. Henigsman, DO
Was this helpful?
1

A molar pregnancy is a noncancerous tumor made of early pregnancy cells. The tumor occurs when there is a problem with the chromosomes. This prevents a pregnancy from developing into a full embryo. A molar pregnancy cannot develop into a healthy pregnancy and will end in either a natural or induced miscarriage, or pregnancy loss. However, most people can have a healthy pregnancy after having a molar pregnancy.

This article will explain a molar pregnancy and its causes, symptoms, and treatment.

What is a molar pregnancy?

a couple are embracing
Evgenij Yulkin/Stocksy United

A molar pregnancy, or hydatidiform mole, is a type of tumor that grows from early pregnancy cells. Molar pregnancy is the most common type of gestational trophoblastic disease (GTD). GTDs are conditions in pregnancy when the placental tissue becomes a tumor.

In a molar pregnancy, the early pregnancy tissue develops into cysts instead of forming a healthy embryo. These cysts cannot supply food and oxygen to an embryo. Usually, the diagnosis is made early on because of vaginal bleeding.

In some cases, if not treated, a molar pregnancy can turn into a rare form of cancer.

What causes a molar pregnancy?

According to the March of Dimes, less than 1% of pregnancies in the United States are molar pregnancies. Molar pregnancies are the result of a problem with chromosomes. Chromosomes contain genes from both parents and hold the instructions for forming the body.

To be a viable pregnancy, an embryo needs 46 chromosomes, 23 from each parent. If there is an incorrect number of chromosomes from either parent, or an irregular chromosome, the pregnancy may not develop as expected.

Types of molar pregnancies

There are two types of molar pregnancies: complete and partial.

Complete molar pregnancy

In a complete molar pregnancy, the placenta or embryo does not form. The chromosomes from the parent with the egg do not get copied, so only one set of chromosomes from the sperm is present. Without both sets of chromosomes, an embryo cannot develop.

Partial molar pregnancy

In this type of pregnancy, part of the placenta forms, and an embryo does start to grow. However, because of a chromosomal irregularity, the embryo cannot survive long. In a partial molar pregnancy, there are two sets of chromosomes from the male parent and one set from the other parent. This makes 69 chromosomes rather than 46. 

What are the risk factors for a molar pregnancy?

Risk factors for having a molar pregnancy include:

  • age under 20 years or over 35 years, higher risk after 40 years
  • two or more previous pregnancy losses
  • a previous molar pregnancy
  • dietary deficiencies, such as folate, protein, or beta-carotene

Learn more about pregnancy loss here.

How do doctors diagnose molar pregnancy?

A doctor usually will order a uterine ultrasound to diagnose a molar pregnancy.

Your doctor may also order lab tests to measure the level of human chorionic gonadotropin (hCG) in your blood. The hCG level rises either faster or slower in molar pregnancies than in healthy pregnancies. 

What are the symptoms of a molar pregnancy?

In the beginning, a molar pregnancy may feel typical. The placenta produces the pregnancy hormone hCG, which gives you a positive pregnancy test. You may also experience expected early pregnancy symptoms like sore breasts and morning sickness.

Learn more about the first month of pregnancy here.

However, the symptoms of a molar pregnancy begin within the first 3 months of getting pregnant. You may experience:

  • vaginal bleeding
  • cysts that look like grapes coming out of your vagina
  • severe nausea and vomiting (sometimes requiring hospitalization)
  • pelvic pain or pressure

Contact your doctor right away if you experience these symptoms. 

Molar pregnancies can also cause:

What are the treatments for a molar pregnancy?

In many cases, a molar pregnancy leads to a natural pregnancy loss. The body will flush out blood and tissue through the vagina, much like a heavy period.

In some cases, doctors recommend a procedure called dilation and curettage (D and C) to remove tissues of the molar pregnancy from the uterus. This procedure takes place in a surgical center and under sedation. First, the doctor dilates the cervix. A spoon-like instrument then is entered into the uterus to remove any pregnancy tissues.

Learn more about recovery after dilation and curettage.

Your doctor will continue to monitor your hCG levels every week until they reach a nonpregnant level. After that, you may need monthly follow-ups for 6 months.

Watching your hCG level ensures that there is no tissue of the molar pregnancy left in your uterus. During this time, the recommendation is to avoid getting pregnant. 

In rare cases, molar tissues continue to grow after the D and C procedure. This is called persistent GTD. Treatment may be a hysterectomy, which is removal of the uterus, or chemotherapy.

Can you get pregnant again after a molar pregnancy?

Yes, getting pregnant after a molar pregnancy is possible, and many people do. However, it is best to wait until your doctor has determined that molar tissue no longer is growing in your uterus. 

After having a molar pregnancy, there is a 1% risk of having another molar pregnancy, according to the National Institutes of Health (NIH).

Learn more about what to expect after a pregnancy loss.

Other frequently asked questions

Following are questions people also ask about molar pregnancy.

When do molar pregnancy symptoms start?

Symptoms of a molar pregnancy, such as bleeding and cramping, usually appear in the first trimester during weeks 6–12. 

What is the main cause of molar pregnancy?

The main cause of a molar pregnancy is an irregularity with the chromosomes involved in the pregnancy. There may not be enough chromosomes in the egg, or there may be too many. 

Is a molar pregnancy a baby?

A molar pregnancy does not form an embryo. It will not have enough healthy cells to develop into a baby. 

Is a molar pregnancy considered a miscarriage?

A molar pregnancy is not a viable pregnancy. It will always end in either a spontaneous or medically induced miscarriage. 

Will a molar pregnancy test positive?

A molar pregnancy will result in a positive pregnancy test. The molar tumor produces the hCG pregnancy hormone.

Who is at risk for molar pregnancy?

Molar pregnancies are rare, but they can happen to anyone. Someone who has had a previous molar pregnancy has a higher risk of having another one. In addition, people under age 20 or over age 35 have a higher risk of molar pregnancy.

Summary

A molar pregnancy is nonviable, meaning that it cannot become a healthy pregnancy. A problem with the chromosomes prevents the pregnancy from developing correctly.

At first, someone with a molar pregnancy may have expected pregnancy symptoms, such as morning sickness and sore breasts. Within the first trimester, however, specific molar pregnancy symptoms will appear. These include vaginal bleeding, severe nausea, and vomiting. A uterine ultrasound will verify the diagnosis.

In most cases, a molar pregnancy will result in a miscarriage that happens on its own. If a natural pregnancy loss does not occur, your doctor may suggest a D and C to remove all pregnancy tissues from the uterus. Removing these tissues is necessary to prevent further complications.

Your doctor may monitor you for 6 months after a molar pregnancy to make sure no molar tissue grows back. Your doctor will advise you on how long you should avoid another pregnancy. Most of the time, people can have healthy pregnancies after a molar pregnancy.

Was this helpful?
1
Medical Reviewer: Stacy A. Henigsman, DO
Last Review Date: 2022 Jun 28
View All Pregnancy Articles
THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
  1. Al-Talib, A. A. (2016). Clinical presentation and treatment outcome of molar pregnancy: Ten years experience at a tertiary care hospital in Dammam, Saudi Arabia. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5009886/
  2. Gestational trophoblastic disease treatment (PDQ) – health professional version. (2022). https://www.cancer.gov/types/gestational-trophoblastic/hp/gtd-treatment-pdq
  3. Molar pregnancy. (2017). https://www.marchofdimes.org/complications/molar-pregnancy.aspx
  4. Molar Pregnancy. (2018). https://www.betterhealth.vic.gov.au/health/healthyliving/pregnancy-related-cancer#risk-factors-for-molar-pregnancy