What is a molar pregnancy?

A hydatidiform mole, also known as a molar pregnancy, is a noncancerous tumor that grows inside the uterus, forming from tissue that develops after fertilization. In a molar pregnancy, the fertilized egg doesn’t develop into an embryo, but rather into a harmless mass of cysts.

Unfortunately, molar pregnancies cannot develop into healthy, viable pregnancies. They are treated by removing the abnormal tissue from the uterus using either medication or surgery. Choice of treatment depends on the type, size, and age of the molar pregnancy.

Two types of molar pregnancies

The different types of molar pregnancies are characterized by the process in which they began.

  • Partial molar pregnancy: This type of molar pregnancy occurs when an egg is fertilized by two sperm cells, resulting in the zygote (fertilized egg) having 69 chromosomes instead of the normal 46. Some fetal tissue will form in a partial molar pregnancy, but it is not viable.
  • Complete molar pregnancy: This type occurs when an egg that contains no genetic information is fertilized by a sperm cell. No fetal tissue will develop within the molar tissue, and it is not viable.

Risk factors for molar pregnancy

Some women are at higher risk than others for developing a molar pregnancy. Risk factors include the following.

  • Personal history of molar pregnancy
  • Pregnant women over 35 years old
  • Pregnant women younger than 25 years old
  • Pregnant women living in Asia, the South Pacific, or Mexico

Symptoms of a molar pregnancy

Very often, a molar pregnancy will seem like a normal pregnancy through the first several weeks of gestation. This is because molar tissue releases hCG, the hormone responsible for pregnancy symptoms, just like normal pregnancy tissue. However, there are certain signs you can look for that might clue you in to the presence of a molar pregnancy.

  • Vaginal bleeding during the first trimester. This blood could be any color, ranging from dark brown to bright red.
  • Severe nausea and vomiting continuing after the first trimester. Sometimes, this is so intense that the woman has to be hospitalized.
  • Grape-like cysts passing from the vagina. These look like small sacs that are filled with fluid.
  • Larger pregnancy size than expected based on gestational age. Particularly with complete molar pregnancies, women may feel “bigger” than they expect at a specific point in pregnancy.
  • Preeclampsia-like symptoms in the first or early second trimester. This includes high blood pressure and swelling of the legs, ankles, or feet. Because preeclampsia doesn’t normally develop this early in pregnancy, these symptoms strongly point to a molar pregnancy.
  • Symptoms of hyperthyroidism. These can be caused by very high levels of hCG associated with molar pregnancies, and symptoms range from a rapid heart rate, trembling hands, and unexpected weight loss.

If you notice any of the above symptoms, you should talk to your provider right away. He or she may suspect a molar pregnancy based on specific signs and symptoms, and will perform blood work and an ultrasound to confirm the diagnosis. A blood test will show higher than normal hCG levels for the pregnancy date. Additionally, an ultrasound will show no fetal parts or movement, and fetal heart sounds will not be heard.

Treatment and beyond

To treat a molar pregnancy, the molar tissue must be removed from the uterus. This is usually done through a procedure called a dilation and curettage (D&C), which is performed vaginally through a woman’s cervix. It involves the provider giving the woman anesthesia, and then removing the molar tissue from her uterus using a vacuum device. Some women choose to have their uterus removed in a procedure called a hysterectomy, but this procedure can only be used on women who don’t want to become pregnant in the future.

  • Follow-up: After the initial treatment, women will be followed regularly by their provider to make sure no more molar tissue grows in the uterus. Their provider will measure hCG levels every month for 12 months to make sure the hormone goes back to pre-pregnancy levels.
  • Contraception: Becoming pregnant again too soon after a molar pregnancy puts you at a high risk for recurrence of the condition. Therefore, it is very important to use a reliable form of contraception for 6-12 months after a molar pregnancy. 

Recovering from a molar pregnancy can be difficult. It usually involves a mix of emotional and physical healing. Every experience is different, and many women don’t feel emotionally healed for some time after a molar pregnancy. It is important that the woman has the support and care she needs to get back to a good physical and mental state of being after a molar pregnancy.

  • Mayo Clinic Staff. “Molar Pregnancy: Symptoms.” MayoClinic. Mayo Foundation for Medical Education and Research, Oct 24 2014. Web.
  • “Molar pregnancy.” MarchofDimes. March of Dimes Foundation, May 2014. Web.
  • “Hydatidiform mole.” MedlinePlus. US National Library of Medicine, Nov 14 2014. Web.
  • Kerri Durnell Schuiling, Frances E. Likis. Women’s Gynecologic Health. 3rd edition. Jones & Bartlett Learning, Aug 2016. Web.
  • The American Cancer Society medical and editorial content team. “What are the Risks For Gestational Trophoblastic Disease?” Cancer. American Cancer Society, Feb 6 2014. Web.  
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