Molar Pregnancy

A rare condition in which part of the placenta develops into a tumour

  • More common over the age of 35
  • More common in Asian women
  • Lifestyle is not a significant factor

In about 1 in 2,000 pregnancies, part of the placenta develops into a hydatidiform mole, a tumour that looks similar to a small bunch of grapes. Although a hydatidiform mole is noncancerous, in a few cases it develops into a cancerous tumour (see Choriocarcinoma). A hormone called human chorionic gonadotropin (HCG), which is normally produced by the placenta in pregnancy, is present in very high levels in molar pregnancy. In most molar pregnancies, the tumour prevents a fetus from developing, but occasionally an abnormal fetus develops. Placental cells left after a miscarriage or pregnancy can develop into a hydatidiform mole.

In about 1 in 10 molar pregnancies, a hydatidiform mole invades the wall of the uterus. In about 3 in 100 cases, a hydatidiform mole becomes cancerous, and the cancer may spread. Molar pregnancy occurs more often in women over the age of 35 and is more common in Asian women. The cause is unknown. In many cases, molar pregnancy is detected during a routine ultrasound scan in early pregnancy (see Ultrasound scanning in pregnancy).

What are the symptoms?

A hydatidiform mole exaggerates some of the symptoms of a normal, healthy pregnancy, such as tiredness, and it may also produce the following:

  • Bleeding from the vagina and passing material that looks like grapes.

  • Extreme nausea and vomiting (see Hyperemesis).

A hydatidiform mole grows faster than a normal fetus, making the uterus larger than normal for the stage of pregnancy. If the pregnancy progresses, additional problems, including pre-eclampsia and anaemia, may develop.

What might be done?

If you are experiencing severe nausea and vomiting or if your uterus appears much larger than normal for the stage of your pregnancy, your doctor may suspect a molar pregnancy. He or she will arrange for an ultrasound scan to look for signs of a molar pregnancy, and your blood will be tested to measure levels of HCG. If a hydatidiform mole is diagnosed, the abnormal tissue will be removed from the uterus under general anaesthesia.

What is the prognosis?

Most women recover fully and need no further treatment once the molar pregnancy has been removed. However, a choriocarcinoma sometimes develops and further treatment, such as chemotherapy, is required.

It is important that women who have had a molar pregnancy should have regular urine tests for at least 2 years to measure HCG levels and ensure that any cancerous changes are detected early. It is advisable not to conceive for at least 1 year after treatment for a hydatidiform mole because the risk of choriocarcinoma is greatest during this time and a pregnancy will interfere with HCG monitoring. In up to 3 in 100 subsequent pregnancies, a hydatidiform mole recurs.

From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.

The subjects, conditions and treatments covered in this encyclopaedia are for information only and may not be covered by your insurance product should you make a claim.

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