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Molar Pregnancy

Despite its name, a molar pregnancy (also known as a hydatidiform mole) is actually not a viable pregnancy at all. A molar pregnancy is a form of gestational trophoblastic disease in which a problem occurs at conception, resulting in a mass of tissue that grows and mimics a pregnancy. Although a molar pregnancy cannot result in a birth, women with a molar pregnancy can still experience many of the symptoms of pregnancy. This uncommon condition requires treatment in order to prevent serious complications that can affect the health of the mother

Who is at Risk for Molar Pregnancy?

The factors that can put a woman at risk for a molar pregnancy are age, previous molar pregnancies, previous miscarriages, and a diet lacking in carotene and vitamin A.

  • Age: Women who are over the age of 35, and especially those over the age of 45, are more likely to develop a molar pregnancy. Young women and girls under the age of 20 are also at an increased risk.
  • Previous molar pregnancy: The risk of a molar pregnancy for a woman who has previously had one is about 10 times that of a woman who has never had a molar pregnancy.
  • Previous miscarriages: Women who have had a miscarriage are at increased risk of developing a molar pregnancy.
  • Low intake of carotene: Carotene is a form of vitamin A. Not getting enough vitamin A through diet or supplements can increase the risk of a molar pregnancy.

How Common are Molar Pregnancies?

Molar pregnancies are not common; in the United States, they occur in about one in every 1,000 pregnancies.

Types of Molar Pregnancy

The two main forms of molar pregnancy are called complete moles and partial moles. In both forms, there is a problem with either the egg or the sperm at the time of conception.

  • Complete moles: A molar pregnancy is called a complete mole when there is no actual embryo tissue at all. In this situation, all the chromosomes come from the sperm; the egg either has no chromosomes or they are dormant for some reason. The resulting tissue grows in size, but it is not a viable fetus.
  • Partial moles: A partial mole forms when an egg is fertilized by two sperm, or by one sperm whose chromosomes have duplicated. The result is an embryo that has an extra set of chromosomes. The embryo does not grow normally. Instead, part of the placenta develops into the rapidly growing molar tissue. Some of the placental tissue may also be normal. At this point the embryo is malformed and will not survive.

Symptoms of a Molar Pregnancy

Some of the symptoms of a molar pregnancy can be very similar to those of early pregnancy, and include:

The symptoms that can occur with a molar pregnancy that are not typical of a viable pregnancy are:

  • Vaginal bleeding (bright red to dark brown) in the first trimester
  • Uterus increasing in size
  • Severe nausea and vomiting
  • Hyperthyroidism
  • Abdominal discomfort (though this is uncommon)
  • Passing tissue from the vagina

Diagnosing Molar Pregnancy

A molar pregnancy may be diagnosed during the first trimester with a trans-vaginal ultrasound. For this type of ultrasound, a wand is inserted into the vagina in order to better view the uterus. During the ultrasound, the physician may note one of several signs of a molar pregnancy:

  • Complete molar pregnancy — An ultrasound of a complete molar pregnancy may show the absence of an embryo or amniotic fluid, a thickened placenta, or ovarian cysts.
  • Partial molar pregnancy — During an ultrasound, a partial molar pregnancy may be diagnosed by the small size of the fetus, a low level of amniotic fluid, or a thickened placenta.

A suspected molar pregnancy can also be diagnosed by testing hCG levels. In a molar pregnancy, the hCG level might be present in the blood in a higher concentration than it is in a viable pregnancy.

Treatment for a Molar Pregnancy

To treat a molar pregnancy, the growing tissue must be removed from the uterus. This is commonly done with a procedure known as a dilation and curettage, often referred to as D & C. This is a common outpatient procedure that can be done in a gynecologist’s office or in a hospital setting. During a D & C, a special tool is used to vacuum out any molar tissue that is in the uterus. The patient lies on a gynecological exam table with her feet in stirrups, and she is typically given a general anesthetic. The vagina is opened with a speculum (similar to the device that is used during a routine PAP smear). The cervix must be dilated to about six to nine centimeters in order to remove the molar tissue. The procedure generally takes fifteen minutes to half an hour.

Most women go home within a few hours after a D&C, and are able to resume their normal activities within a few days. Cramping, spotting, and light bleeding may occur for a few days after a D & C procedure.

After the D & C, the hCG level is often monitored for six months to a year. If hCG  is still found in the blood, it could mean that additional treatment for the molar pregnancy is necessary.

In most cases, women are advised to refrain from attempting to become pregnant again for about six months to a year after treatment for a molar pregnancy. This is to ensure that all of the molar tissue has been removed and does not recur.

In extreme cases, the physician may decide to do a hysterectomy, removing all the molar tissue in the uterus, thereby eliminating the risk of any leftover tissue causing further complications. Women who have decided not to become pregnant in the future may also opt for a hysterectomy after a molar pregnancy.

Complications from a Molar Pregnancy

Some women who experience molar pregnancy also develop conditions such as preeclampsia, hyperthyroidism, or anemia. If any of these are present along with the molar pregnancy, they will need to be treated.

Every effort is made to remove all of the molar tissue from a molar pregnancy, but in about 20 percent of complete and 5 percent of partial cases of molar pregnancy, there may be some cells left inside the uterus. These cells will continue to grow unchecked, resulting in persistent gestational trophoblastic disease (GTD). In some cases of GTD, the molar tissue could grow into the uterine wall. This condition is treated either with chemotherapy or with a hysterectomy. In cases of cancerous GTD (choriocarcinoma), treatment with other cancer-treating drugs may also be necessary. Fortunately, the cure rate for GTD is near 100 percent.

Coping with Pregnancy Loss

Because molar pregnancy is often diagnosed about eight weeks into what is typically assumed to be a normal pregnancy, affected women and their families may experience feelings of loss. After the molar pregnancy has been treated, it’s important to take time to grieve the loss of the pregnancy. If a woman decides to become pregnant again, the chance of developing another molar pregnancy is low—between 1 and 2 percent—which means that any future pregnancy has an excellent chance of being viable and resulting in a live birth.

    [Page updated June 2017]