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Molar pregnancy

A molar pregnancy is when an egg is fertilised (conception) but it's genetically faulty – it has either too many or not enough genes.

Some tissue grows and implants, but it always ends in a miscarriage. Nobody knows exactly why this happens, but it happens in about one in every 700 pregnancies.

Molar pregnancy is also called hydatidiform (hi-dat-id-e-form) mole or gestational trophoblastic (jes-tay-shun-al tro-fo-blas-tik) disease (GTD).

There are two types of molar pregnancy.

Women with a molar pregnancy often have higher levels of the pregnancy hormone hCG (human chorionic gonadotrophin).

Symptoms of molar pregnancy

You may have the usual symptoms of pregnancy such as sore breasts and feeling sick or vomiting. Most women will also have vaginal bleeding.

Diagnosing molar pregnancy

An ultrasound scan carried out because of bleeding or as part of routine care will show there is not a pregnancy that can continue.

Other changes seen on the ultrasound will also suggest this could be a molar pregnancy.

If your doctor, midwife or LMC suspects you may have a molar pregnancy, you may also have a blood test to check your hCG levels.

The only way to confirm the pregnancy was a molar pregnancy is by examining and testing the tissue under a microscope, which takes about 10 days.

Treating molar pregnancy

If your hCG levels are high and your ultrasound suggests you may have a molar pregnancy, your doctor will recommend you have a small operation to remove the pregnancy tissue. This is called an ERPOC or evacuation of retained products of conception, also known as a D&C. The tissue can then be examined and tested.


Most women's hCG levels will drop back to normal after a molar pregnancy, indicating that all the molar pregnancy cells have gone. But some of the abnormal molar pregnancy cells stay in the wombs of about one in 10 women. These may then grow and spread around their body, which is known as gestational trophoblastic neoplasia (nee-o-play-si-a) or GTN. This is a type of cancer, but it can be treated successfully with chemotherapy.

If the abnormal cells are present, they keep making pregnancy hormone (hCG). So, women who have had a molar pregnancy should have blood tests to check their hormone levels to determine if the abnormal cells have gone.

The first test is usually done about 10 days after the operation. You'll then be seen about two weeks after this, when your doctors will be able to confirm whether there was definitely a molar pregnancy. If there was, you'll need further testing for at least six months.

Care after a molar pregnancy

A molar pregnancy doesn't affect your fertility at all. For this reason, it's very important to use contraception to avoid getting pregnant for six months after your blood hCG levels have gone back to normal. This is because being pregnant also boosts your hormone levels so it's impossible to know if your hormones are rising because of pregnancy or because the abnormal cells are coming back.

In any future pregnancies you should also get blood tests at six and 12 weeks to check your hormone levels to make sure the abnormal cells have not come back.

After a molar pregnancy you can use hormonal contraception (the Pill, implant or injection) or condoms to avoid getting pregnant.

A second molar pregnancy is rare, only happening to around one in 80 women. In any future pregnancies, you should have an ultrasound scan at seven to eight weeks, to make sure the pregnancy is not another molar pregnancy.

If you have further questions, ask the doctor in the molar pregnancy clinic.

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Written by Gynaecology Service Christchurch Women's Hospital. Adapted by HealthInfo clinical advisers. Last reviewed January 2022.


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