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A molar pregnancy is when an egg is fertilised (conception) but it is genetically faulty. This means 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 1 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).
You may have the usual symptoms of pregnancy such as sore breasts and feeling sick or vomiting. Most women will also have vaginal bleeding.
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 lead maternity carer (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. This takes about 10 days.
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. It is 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 1 in 10 women. These may then grow and spread around their body.
This is known as gestational trophoblastic neoplasia (nee-o-play-si-a) or GTN. It 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 tested 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 will then be seen about 2 weeks after this, when your doctors will be able to confirm whether there definitely was a molar pregnancy. If there was, you will need further testing for at least 6 months.
A molar pregnancy does not affect your fertility at all. So, it is very important to use contraception to avoid getting pregnant for 6 months after your blood hCG levels have gone back to normal. Being pregnant also boosts your hormone levels. This means it would be impossible to know if your hormones were rising because of pregnancy or because the abnormal cells were coming back.
In any future pregnancies, you should also get blood tests at 6 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 1 in 80 women. In any future pregnancies, you should have an ultrasound scan at 7 to 8 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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Detailed information about molar pregnancy.
Written by Gynaecology Service Christchurch Women's Hospital. Adapted by HealthInfo clinical advisers. Last reviewed November 2024.
Review key: HIPLT-311303