What Is a Molar Pregnancy?

A molar pregnancy is a pregnancy complication where a non-viable fertilized egg develops into a tumor rather than a fetus. The mass often resembles a clump of grapes when viewed on an ultrasound.

Molar pregnancies are usually not cancerous, but sometimes the tumor can be malignant. Since the pregnancy cannot be carried to term and because the complication can pose health risks to the pregnant person, treatment involves terminating the pregnancy, usually by dilation and curettage (D&C).

Types of Molar Pregnancies

Molar pregnancies fall into several categories. Certain types are more difficult to treat and can pose longer-term health complications. 

Hydatidiform Mole

Hydatidiform moles fall into one of two categories: complete or partial. A complete mole contains no maternal DNA but two sets of paternal DNA. With a complete mole, no embryo forms.

A partial mole contains a normal amount of maternal DNA and double the amount of paternal DNA. With a partial mole, an embryo forms along with an abnormal placenta.

In both cases, the placenta does not develop or function properly, and the pregnancy is not viable. In very rare cases, a partial molar pregnancy can result in a live fetus. In most cases, the embryo develops severe congenital disabilities, and the growth ultimately takes over the embryo.

Invasive Mole

An invasive mole grows into the deep muscle tissue of the uterus. These kinds of moles can originate from both complete and partial moles, but complete moles have a greater tendency to become invasive. 

Sometimes an invasive mole can grow all the way through the uterine wall, which can result in life-threatening hemorrhage. Invasive moles can metastasize (spread throughout the body). 

Choriocarcinoma

Choriocarcinoma is a malignant (cancerous) mole. Choriocarcinomas can metastasize very quickly, so early detection and treatment are important.

Although choriocarcinomas are most commonly a molar pregnancy complication, they can also form in the absence of a pregnancy. Less commonly, they develop after a miscarriage, ectopic pregnancy, or normal pregnancy.

Choriocarcinoma may be suspected if:

• Pregnancy hormone levels increase at abnormal rates
• There is vaginal bleeding
• You are experiencing respiratory difficulties 

Most of the time, a molar pregnancy is noncancerous. In these instances, the growth is confined to the uterus. After treatment, most noncancerous molar pregnancies are resolved. However, a person who has had a mole develop will need to be closely monitored for six or more months following the pregnancy.

Placental-Site Trophoblastic Tumor (PSTT)

Placental-site trophoblastic tumors are extremely rare malignant moles that grow between the placenta and the lining of the uterus. They account for only 0.23% to 3.00% of GTDs.

PSTTs tend to become invasive and can develop after a complete or partial mole is removed, but most often develop after a full-term pregnancy. Sometimes PSTTs are not detected until years after a full-term pregnancy.

Most often, PSTTs do not metastasize, but they can. They are resistant to chemotherapy, so hysterectomy (surgery to remove the uterus) is the standard treatment.

Epithelioid trophoblastic tumor (ETT)

ETT is the rarest form of GTD, accounting for 1% to 2% of all GTDs. Like PSTTs, most often develop following a full-term pregnancy. These moles can take years to develop. 

Chemotherapy is often ineffective for treating ETTs; surgery to remove the uterus is the standard treatment. If the mole has metastasized, however, chemotherapy is an essential component of treatment.

Signs/Symptoms of Molar Pregnancy

Symptoms of molar pregnancy are similar to other pregnancy-related complications, so it’s important to have your symptoms evaluated by your healthcare provider. Symptoms include:

• Vaginal bleeding
• Unusually high pregnancy hormone levels
• Anemia
• High blood pressure
• Unusual uterine growth
• Pelvic pain
• Extreme nausea or vomiting

Causes

Molar pregnancy is caused by chromosomal abnormalities that disrupt the development of the embryo. In a healthy pregnancy, an embryo develops from a set of maternal and paternal chromosomes.

In a molar pregnancy, the maternal chromosomes may be missing and the paternal chromosomes are duplicated (complete hydatidiform mole), or two sperm fertilize an egg and there are three sets of chromosomes (partial hydatidiform mole).

These errors result in the development of a tumor instead of an embryo and a placenta. Further gene changes may be seen in malignant moles.

Diagnosis

If you are exhibiting symptoms like unusually high hormone levels or rapid uterine growth, your healthcare provider may suspect a molar pregnancy. A transvaginal ultrasound can usually confirm a diagnosis, especially if the mole is complete. An ultrasound image of a mole often appears like a clump of grapes or a honeycomb.

Further testing may be recommended in order to determine what type of mole you have and whether it has spread to other parts of the body. These tests might include X-ray, computed tomography (CT scans), or magnetic resonance imaging (MRI) to view your chest, head, and abdomen. 

Treatment

Some molar pregnancies resolve in spontaneous abortion (also known as miscarriage), but because it is important to make sure that the entire growth is removed. D&C surgery is the preferred treatment for a diagnosed molar pregnancy. If the mole has spread or if the surgery does not remove all of the mole, further treatment will be required.

Surgery (D&C)

D&C for a molar pregnancy is most often performed by an obstetrician/gynecologist (OB-GYN) and is usually done under general anesthesia. During the surgery, your practitioner will use an instrument to widen the cervix and then use a suction device to remove the contents of the uterus, including the tumor.

Your healthcare provider will then use a curette (a spoon-like instrument) to scrape the uterus, which helps to ensure no remaining tissue is left. You will be given an intravenous drug to induce contractions, which will aid in expelling the uterine contents. It is normal to experience vaginal bleeding and cramping for up to a day following the procedure. 

D&C is typically an outpatient procedure, which means you can go home the same day. Complications can include bleeding, infection, and more rarely difficulty breathing when a piece of trophoblastic tissue breaks off and travels to the lungs.

Surgery (Hysterectomy)

For PSTT and ETT moles, hysterectomy is often the preferred treatment method because those types of moles tend to be invasive, malignant, and resistant to chemotherapy. Hysterectomy involves removing the entire uterus, which means that after the surgery, you will no longer be able to become pregnant.

Hysterectomies can be done abdominally, vaginally, and in some cases laparoscopically. Abdominal surgery is more invasive and is done through an incision made in the abdomen. In laparoscopic surgery, small incisions are made for a camera and instruments.

Vaginal hysterectomy involves removing the uterus through the vagina. Vaginal hysterectomy is less invasive, and recovery is easier. Whether it is done vaginally, abdominally, or laparoscopically will usually depend on the size of your uterus. If your uterus is too large, vaginal hysterectomy is not an option.

Hysterectomy is done under general or regional anesthesia and is performed by an OB-GYN. During the procedure, your healthcare provider will separate the uterus from the ovaries, fallopian tubes, and vagina, then remove the uterus.

Hysterectomy is usually an inpatient procedure, which means you will likely stay in the hospital for a couple of days following the procedure. Depending on whether you had an abdominal or vaginal procedure, recovery can take a few weeks to a month or slightly longer.

Risks of the surgery include excessive bleeding, infection, and damage to surrounding organs and tissue.

Chemotherapy and Radiation

Chemotherapy is a cancer-fighting drug that is usually given intravenously. Chemotherapy may be an important part of treatment if the mole is found to be malignant and especially if it has metastasized.

There are many different chemotherapy drugs. Which drug is best for you will depend on your specific circumstance and how advanced the cancer is.

Side effects of chemotherapy include:

• Hair loss
• Nausea and vomiting
• Loss of appetite
• Fatigue
• Increased chance of infection

Radiation is not often used for treating GTD, unless chemotherapy is proving ineffective. Radiation treatment uses high-energy X-rays to kill cancer cells.

Having a radiation procedure feels very similar to having an X-ray done, although the duration is longer. Side effects are similar to chemotherapy but may also include skin redness and blistering, and diarrhea. 

Monitoring

If you have had any type of molar pregnancy, you will be monitored for six or more months after the mole has been removed. Monitoring includes weekly blood tests to check hormone levels. After hormone levels are normal for three consecutive weeks, levels will be checked monthly for six to 12 months.

Your healthcare provider may advise that you wait to try to conceive following a molar pregnancy until after the hormone level monitoring is complete (six months to a year). That’s because rising hormone levels, while normal in pregnancy, can also indicate that GTD has returned. Pregnancy can make identifying recurrent GTD difficult.

Risk Factors

Molar pregnancy is a rare complication, affecting less than 1 in 1,000 pregnancies (less than 1%).

Risk factors for developing a molar pregnancy include:

• Being younger than 20
• Being older than 40
• A prior molar pregnancy
• A history of miscarriages
• Living in a geographic region where the complication is more common (the Philippines, Mexico, or Southeast Asia)

Coping

Recovering from a molar pregnancy is both physically and emotionally challenging. In addition to concerns about your health, you are also likely grieving the loss of a pregnancy, possibly even the loss of fertility.

Grief over that loss and anxiety about your health and fertility are very normal emotions that many people experience following a molar pregnancy. Seek out support from family members, friends, and people in your community. You may find that talking with a trained therapist helps as well.

Since molar pregnancy is such a rare complication, you may find that most people have a limited understanding of it. Online support groups of people who have gone through something similar may be reassuring and affirming. Remember, you are not alone.  

A Word From Verywell

A molar pregnancy can be a frightening and emotional experience. It’s understandable if you feel fatigued by the ongoing monitoring. Remember that weekly monitoring results in better outcomes.

The risk of developing a subsequent molar pregnancy, while greater than your prior risk, is actually still very small. Most people who have had a molar pregnancy do not develop another molar pregnancy, and most people fully recover.

Discussing your treatment with your healthcare provider, including possible complications and your future options, can be a good way to feel involved.