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Molar Pregnancy - Topic Overview

What is a molar pregnancy?

A molar pregnancy happens when tissue that normally becomes a fetus instead becomes an abnormal growth in your uterus. Even though it isn't an embryo, this growth triggers symptoms of pregnancy.

A molar pregnancy should be treated right away. This will make sure that all of the tissue is removed. This tissue can cause serious problems in some women.

About 1 out of 1,500 women with early pregnancy symptoms has a molar pregnancy.1 This means that 1,499 women out of 1,500 don't have this problem.

What causes a molar pregnancy?

Molar pregnancy is thought to be caused by a problem with the genetic information of an egg or sperm. There are two types of molar pregnancy: complete and partial.

  • Complete molar pregnancy. An egg with no genetic information is fertilized by a sperm. The sperm grows on its own, but it can only become a lump of tissue. It cannot become a fetus. As this tissue grows, it looks a bit like a cluster of grapes. This cluster of tissue can fill the uterus.
  • Partial molar pregnancy. An egg is fertilized by two sperm. The placenta becomes the molar growth. Any fetal tissue that forms is likely to have severe defects.

Sometimes a pregnancy that seems to be twins is found to be one fetus and one molar pregnancy. But this is very rare.

Things that may increase your risk of having a molar pregnancy include:

  • Age. The risk for complete molar pregnancy steadily increases after age 35.2
  • A history of molar pregnancy, especially if you've had two or more.3
  • A history of miscarriage.
  • A diet low in carotene. Carotene is a form of vitamin A. Women who don't get enough of this vitamin have a higher rate of complete molar pregnancy.2

What are the symptoms?

A molar pregnancy causes the same early symptoms that a normal pregnancy does, such as a missed period or morning sickness. But a molar pregnancy usually causes other symptoms too. These may include:

  • Bleeding from the vagina.
  • A uterus that is larger than normal.
  • Severe nausea and vomiting.
  • Signs of hyperthyroidism. These include feeling nervous or tired, having a fast or irregular heartbeat, and sweating a lot.
  • An uncomfortable feeling in the pelvis.
  • Vaginal discharge of tissue that is shaped like grapes. This is usually a sign of molar pregnancy.

Most of these symptoms can also occur with a normal pregnancy, a multiple pregnancy, or a miscarriage.

How is a molar pregnancy diagnosed?

Your doctor can confirm a molar pregnancy with:

Your doctor can also find a molar pregnancy during a routine ultrasound in early pregnancy. Partial molar pregnancies are often found when a woman is treated for an incomplete miscarriage.

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