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Understanding Molar Pregnancy: Causes, Symptoms and Treatment

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Updated July 14, 2014

While devastating, the majority of miscarriages at least involve a relatively swift physical recovery. Molar pregnancies are exceptions to that rule.

Molar pregnancies can have scary health complications, requiring months of precautionary monitoring after treatment, which is usually a D&C. Most of the time molar pregnancies go away without further complications, but the added worries can make coping even more difficult than usual.

Molar Pregnancy Basics:

Molar pregnancies are a type of gestational trophoblastic disease (GTD). It is caused by chromosomal abnormalities during conception.

Molar pregnancies fall in two categories: complete and partial hydatidiform moles. Both are caused by chromosomal problems in the fertilized egg, which leads to overgrowth of pregnancy tissue. Although a partial molar pregnancy may develop into a fetus, the abnormal placenta cannot sustain a pregnancy and the chromosomal problems are not compatible with life. A complete molar pregnancy will not develop a recognizable fetus.

Why Molar Pregnancy Can Be Dangerous:

About 20% of women who have had molar pregnancies will develop one of two serious problems: an invasive mole or choriocarcinoma. Invasive moles are more common. The risk of this condition increases the longer the pregnancy continues without treatment. (Invasive moles can develop before or after surgical treatment.)

Choriocarcinoma is a type of cancer that can develop at the placenta site and spread to the body. While serious, it is almost always treatable with chemotherapy.

Either of these conditions is more likely to occur after complete molar pregnancies; only 2 to 4% of partial moles will develop either condition.

Risk Factors:

A few risk factors, such as a previous molar pregnancy or being over 35, can increase your odds of having a molar pregnancy, but like with other miscarriages, risk factors do not need to be present for molar pregnancy to occur.

In North America, hydatidiform moles of either type occur in about 2 to 3 of every 10,000 pregnancies.

Symptoms:

Women with molar pregnancies may have no specific symptoms, but diagnostic clues that point to molar pregnancy might include higher than average hCG levels (complete molar pregnancy), enlarged ovaries, and early pre-eclampsia.

Vaginal bleeding and nausea occur in most molar pregnancies, but they can also occur in normal pregnancies or typical miscarriages. In addition, molar pregnancies can cause swelling in the abdominal area –- but women with normal pregnancies can “show” early also.

Diagnosis:

Molar pregnancy may be discovered when a heartbeat does not become detectable by 12 weeks, but this can also be true of missed miscarriages. The means of diagnosis is usually by ultrasound, which reveals an abnormal placenta that appears like a bunch of grapes.

Treatment and Recovery:

Some molar pregnancies will miscarry without intervention, but if doctors detect molar pregnancy by ultrasound, they usually recommend a D & C or medication in order to reduce risk of further complications.

Rarely, molar pregnancies might occur in twin conceptions with a hydatidiform mole alongside an otherwise viable pregnancy. In these cases, continuing the pregnancy can pose serious risks to the mother's health (because of a 60% chance of developing persistent GTD) and many choose to terminate the pregnancy, which can be another source of mixed emotions in the grieving process.

Medical Monitoring After Molar Pregnancy:

Because of the risk of developing an invasive mole or choriocarcinoma, doctors recommend that women who had molar pregnancies have continued monitoring for several months. The monitoring usually includes weekly or monthly hCG blood tests, because if the hCG fails to decrease or begins to rise again, this can be a symptom of persistent GTD.

If the woman has three consecutive negative hCG blood tests, she is most likely out of the danger zone. Some doctors are less aggressive about monitoring women who had partial molar pregnancies, because the odds of complications are lower.

Coping with Molar Pregnancy:

Molar pregnancy can involve the same stages of grief as other miscarriages, but like ectopic pregnancy (another potentially dangerous condition), grieving from molar pregnancy can be both a relief that the condition was detected as well as grief for the loss of the expected baby. You might hear comments along the lines of “at least they caught it in time” or “at least it wasn’t a real baby,” but it is perfectly normal to be sad and to grieve. Be sure to seek out support groups and other resources to help you get through the process.

Trying Again After Molar Pregnancy:

The exact waiting period varies, but doctors usually advise waiting at least six months to try to get pregnant again after a molar pregnancy. This advice should always be followed and has a clear medical basis.

Why? Rising hCG levels can be the first indication of invasive moles or choriocarcinoma, and both those conditions are highly treatable when detected. A new pregnancy would also cause hCG levels to rise, and if this happened, doctors would not be able to distinguish the hCG from the new pregnancy from the hCG from a potentially malignant gestational trophoblastic disease-related condition.

Also, because the treatment for invasive moles and choriocarcinoma can involve chemotherapy, pregnancy should be avoided until doctors can be sure that the need for chemotherapy will not arise.

About 1% to 2% of women who had a molar pregnancy will have another one, so your doctor may want to follow up with early ultrasounds and hCG blood tests in your next pregnancy to rule out a repeat molar pregnancy.

Sources:

American Cancer Society, “What Is Gestational Trophoblastic Disease?Detailed Guide: Gestational Trophoblastic Disease May 2006. Accessed 26 Jan 2008.

American Pregnancy Association, “Molar Pregnancy.” Mar 2006. Accessed 26 Jan 2008.

March of Dimes, "Ectopic and Molar Pregnancy." Quick Reference and Fact Sheets 2005. Accessed 26 Jan 2008.

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