Molar pregnancy

Most pregnancies end with the birth of a healthy baby. But sometimes things may go wrong, like in a molar pregnancy. A molar pregnancy always ends in pregnancy loss. And without treatment right away, it can be life-threatening for a pregnant woman. 

What is a molar pregnancy? 

A molar pregnancy (also called a hydatidiform mole) is when tissue in the uterus (womb) forms into an abnormal growth or tumor instead of the placenta. In a healthy pregnancy, the placenta grows in your uterus and supplies your baby with food and oxygen through the umbilical cord. 

A molar pregnancy is a type of gestational trophoblastic disease (also called GTD). This is a group of conditions that cause tumors to grow in the uterus. 

There are two kinds of molar pregnancy: 

  1. Partial molar pregnancy. In this condition, there’s an abnormal placenta and an abnormal embryo. An embryo is a fertilized egg that results when an egg and sperm combine. In this condition, the embryo may start to grow, but it can’t survive.
  2. Complete molar pregnancy. In this condition, there is an abnormal placenta but no embryo. 

If not treated, a molar pregnancy can be dangerous to the woman. It sometimes can cause a rare form of cancer. About 1 in 1,000 pregnancies in the United States is a molar pregnancy.

How do you know if you have a molar pregnancy?

A molar pregnancy may seem like a healthy pregnancy at first. But call your health care provider right away if you have any of these signs and symptoms:

  • Vaginal bleeding in the first 3 months of pregnancy
  • Grape-like cysts (fluid-filled sacs)  passing out of the vagina
  • Intense nausea and vomiting 
  • Pelvic pressure or pain. These happens rarely.

When checking your health, your provider may find these conditions: 

  • Your uterus growing too much or too little 
  • High blood pressure early in pregnancy. High blood pressure also is called hypertension. It’s when the force of blood against the walls of the blood vessels is too high. It can stress your heart and cause problems during pregnancy.
  • Cysts on your ovaries. Ovaries are where eggs are stored in your body. You have two ovaries, one on each side of the uterus.   
  • Anemia. This is when you don’t have enough healthy red blood cells to carry oxygen to the rest of your body.
  • A thyroid that is too active (also called hyperthyroidism). The thyroid is a gland in your neck that makes hormones that help your body store and use energy from food.

How is a molar pregnancy diagnosed? 

Your provider uses ultrasound to diagnose a molar pregnancy. He also gives you a blood test to measure the levels of a pregnancy hormone called human chorionic gonadotropin (hCG). A molar pregnancy can cause hCG levels to rise more slowly than in a healthy pregnancy.

How is a molar pregnancy treated? 

If you have a molar pregnancy, your provider does a procedure called dilation and curettage (also called D&C) to remove the tissue from the lining of your uterus. If there’s a lot of molar tissue and you don’t ever want to get pregnant again, you may choose to have a hysterectomy. This is surgery to remove your uterus.  

After your procedure, your provider regularly measures your hCG levels until they’re normal. At this point, your treatment is usually done. Your provider may want to check hCG levels for 6 months to 1 year to be sure there is no more molar tissue in your uterus. Your provider may recommend that you not get pregnant during this time. A pregnancy changes your hCG levels and makes it hard to detect molar tissue. 

If molar tissue is still growing in the uterus, it can cause a condition called persistent GTD. About 1 in 5 women (20 percent) has this condition after a molar pregnancy, usually after a complete molar pregnancy. Persistent GTD can be treated with hysterectomy or chemotherapy. Chemotherapy is medicine used to treat cancer. In rare cases, you may get a cancer-causing form of GTD called choriocarcinoma. This condition is treated with several kinds of cancer medicines.

Who is at risk for having a molar pregnancy?

You may be more likely than other women to have a molar pregnancy if you:

  • Are younger than 20 or older than 35
  • Have had a molar pregnancy before
  • Are of Southeast Asian descent

What causes a molar pregnancy?

A molar pregnancy is caused by an abnormal fertilized egg. Human cells have 23 pairs of chromosomes, or 46 in all. Chromosomes are the structures that hold genes. A gene is part of your body’s cells that stores instructions for the way your body grows and works. Genes are passed from parents to children. For each pair of chromosomes, you get one from your mother and one from your father. 

In a molar pregnancy, there is an extra set of chromosomes from the father. This can happen in two ways:

  1. Partial molar pregnancy. There are 23 chromosomes from the mother, but two sets of chromosomes from the father. The embryo has 69 chromosomes instead of 46. This can happen when the father’s chromosomes are copied or when two sperm fertilize one egg. 
  2. Complete molar pregnancy. The chromosomes from the mother’s egg are lost or not working, and the ones from the father are copied. So all of the chromosomes come from the father.

If you've had a molar pregnancy before, can you go on to have a healthy pregnancy? 

Yes. Women who've had a molar pregnancy usually can go on to have a healthy pregnancy later. The risk of having another molar pregnancy is only about 1 to 2 in 100 women (1 to 2 percent). 

Last reviewed: May, 2014