What Is a Molar Pregnancy: Symptoms & Prevention

Published June 2nd, 2022 by Bridget Reed
Fact Checked by
Camille Freking
Medically Reviewed:
Chris Riley

A normal pregnancy develops after an egg is fertilized with sperm and implanted into the uterus.

Sometimes, the development process can go awry and lead to pregnancy complications

Out of the possible pregnancy complications, a molar pregnancy is incredibly rare. However, if this rare complication occurs, the baby cannot develop, and the pregnancy cannot continue. 

In this guide from USA Rx, we go over everything you need to know about molar pregnancies, including their causes, symptoms, treatment, and prevention. 

What Is a Molar Pregnancy?

A molar pregnancy (or hydatidiform mole) is a gestational trophoblastic disease. It happens when there’s an abnormal placenta (i.e. the placenta doesn’t develop as it should) that grows to resemble a cluster of grapes in a sonogram. 

The placenta is an organ that grows in the uterus during pregnancy. It’s responsible for providing nutrients and oxygen to the growing baby while eliminating waste. 

In a molar pregnancy, abnormal tissue develops in the uterus instead of the placenta. This molar tissue prevents the baby from getting the nourishment that they need, which means the baby won’t be able to develop properly.

Ultrasound scans during the first trimester can reveal molar pregnancies before other symptoms have yet appeared. 

molar pregnancy

There are two types of molar pregnancies: partial mole and complete mole. Both typically result in pregnancy loss. 

In a partial molar pregnancy, a tumor forms along with an embryo.

The tumor prevents the embryo from developing properly, which can lead to severe birth defects. 

In a complete molar pregnancy, the entire placental tissue is abnormal. As such, no embryo can form.

Despite this, the tumor produces a pregnancy hormone called human chorionic gonadotropin (hCG), which can produce a positive result on a pregnancy test

Ultrasound scans during the first trimester can reveal molar pregnancies before other symptoms have yet appeared. 

In North America, about 1 in 1,000 pregnancies are molar pregnancies.

However, in some developing countries, molar pregnancy incidence is as high as 1 in 100. 

Having one molar pregnancy can increase the risk of having another one in the future.

However, having a healthy pregnancy is still more than possible after experiencing a molar pregnancy. 

Most molar pregnancies will resolve on their own, with grape-like cysts (which are sacs filled with fluid) passing naturally out of the vagina.

That said, a molar pregnancy may need further treatment.

Some molar pregnancies result in an invasive mole or gestational trophoblastic neoplasia (or persistent GTD) — a rare, but treatable, form of cancer or choriocarcinoma. 

After seeing your OBGYN initially after the cysts pass, you should schedule a follow-up appointment to ensure you are on the road to wellness.

What Are the Symptoms of a Molar Pregnancy? 

A molar pregnancy may feel just like a normal pregnancy in its early stages. You may have a positive pregnancy test result, a missed period, morning sickness, and breast tenderness. 

However, as time goes by, you’ll notice a few abnormal symptoms that tell you that your pregnancy is not going the way it should. 

Some typical molar pregnancy symptoms include:

  • Bleeding: In early pregnancy, some light spotting is normal during implantation. This very light bleeding should generally only last one or two days early in the first trimester. However, during a molar pregnancy, vaginal bleeding may be heavier, darker in color, and produce blood clots.
  • Severe nausea: In early pregnancy, the placenta’s growth coincides with the body’s increasing hCG levels, aka the pregnancy hormone. In women with a molar pregnancy, there may be more placenta tissue than is normal, which can lead to severe nausea and even vomiting beyond the mild nausea known as morning sickness. 
  • Pelvic pain: In a molar pregnancy, the placenta grows a lot faster than it should, which can lead to rapidly increasing pressure on the pelvis, and subsequently, moderate to severe pelvic pain
  • High hCG levels: While hCG levels rise as part of a healthy pregnancy, a molar pregnancy has much higher than normal levels. A blood test can help measure the hCG to check if it’s within range. 

You may also experience high blood pressure (preeclampsia), thyroid issues (specifically, hyperthyroidism), weight loss, or increased appetite, though not all women will experience these particular symptoms. 

What Causes a Molar Pregnancy? 

Women carry hundreds of thousands of eggs that can potentially be fertilized. If some of these eggs are abnormal, the body gets rid of them. In rare cases though, some of these abnormal eggs can get fertilized by sperm. 

The abnormal, fertilized egg can prevent normal fetal development, and lead to molar pregnancy. In the same line, abnormal sperm can fertilize a perfectly healthy egg and lead to molar pregnancy. 

While there’s nothing that a mother (or father) can do to “cause” a molar pregnancy, three main factors increase someone’s chances of having a molar pregnancy.

The first risk factor is age. Molar pregnancies are more common in women who are under 20 or over 35. 

That said, it’s not necessarily a person’s age in and of itself that increases the chances of a molar pregnancy, but the factors associated with age.

For instance, the risk of chronic health conditions goes up with age, which leads to a higher risk of pregnancy complications.

A history of molar pregnancy can also increase the chances of having another one in the future.

However, taking ample time to recover after an initial molar pregnancy can significantly increase the chances of having a healthy pregnancy. 

Last, vitamin A deficiency has been linked to molar pregnancies.

However, while this deficiency is very common in developing countries, it is fairly uncommon in North America, and so is rarely the cause of molar pregnancies in American women. 

How Can You Prevent a Molar Pregnancy? 

There is very little that you can do to prevent a molar pregnancy. 

If you’ve had a previous molar pregnancy, you can reduce your chances of complications by waiting to try for pregnancy again for at least one year.

Your doctor can monitor your levels of the pregnancy hormone hCG to make sure that the tumor has stopped growing.

Once your hCG levels have stabilized, your doctor will discuss with you the next steps for getting pregnant.

In Conclusion 

A molar pregnancy begins during fertilization when an unhealthy egg is fertilized by a healthy sperm (or vice versa).

A molar pregnancy leads to tumor growth in the placenta, or may result in  abnormal placenta tissue overall, both of which prevents a normal pregnancy from ensuing.

Those with a molar pregnancy may experience heavy bleeding with blood clots, severe nausea, and pelvic pain. 

There isn’t much that you can do to prevent a molar pregnancy.

However, by seeking the right healthcare treatment options and taking ample time to recover before attempting another pregnancy, you generally have very high chances of a perfectly healthy baby in the future. 

References and Sources: 

Epidemiology of Complete Molar Pregnancy | NCBI

Prevention of Post-Mole Malignant Trophoblastic Disease with Vitamin A | NCBI 

Maternal Age and Risk of Labor and Delivery Complications | PMC

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