A molar pregnancy is where a foetus doesn't form properly in the womb and a baby doesn't develop.

A lump of abnormal cells grows in the womb instead of a healthy foetus.

This growth is called a "hydatidiform mole", which can be either:

• a complete mole, where there's a mass of abnormal cells in the womb and no foetus develops
• a partial mole,where an abnormal foetus starts to form, but it can't survive or develop into a baby

A molar pregnancy can usually be treated with a simple procedure to remove the growth of cells from the womb, but cells are sometimes left over and further treatment is needed to remove them.

Symptoms of a molar pregnancy

There are often no signs that a pregnancy is a molar pregnancy.

It may only be spotted during a routine ultrasound scan at 8-14 weeks or found during tests carried out after a miscarriage.

Some women with a molar pregnancy have:

• vaginal bleeding or a dark discharge from the vagina in early pregnancy (usually in the first three months) – this may contain small, grape-like lumps
• severe morning sickness 
• an unusually swollen tummy

But some of these symptoms are fairly common in pregnancy and aren't necessarily a sign that anything is wrong with your baby.

When to get medical help

Contact your midwife or GP if you have any worrying symptoms, such as vaginal bleeding, while you're pregnant.

They may refer you to an early pregnancy assessment service for an ultrasound scan to rule out any problems with your baby.

If you've had a molar pregnancy before and think you might have another one, you can go to an early pregnancy service directly without contacting your midwife or GP first.

Find an early pregnancy service near you on the Association of Early Pregnancy Units website.

Treatment for a molar pregnancy

If an ultrasound scan shows that you have a molar pregnancy, treatment to remove it will be recommended.

Three main treatments can be used:

• Suction removal – the abnormal cells are sucked out using a thin tube passed into your womb through your vagina. This is usually done under general anaesthetic (where you're asleep).
• Medication – if the growth is too large to be sucked out, you may be given medication to make it pass out of your vagina.
• Surgery to remove the womb (hysterectomy) – this may be an option if you don't want to have any more children in the future.

Most women are successfully treated with suction removal and can go home later the same day.

Speak to your doctor about the benefits and risks of the different options.

Monitoring after treatment for a molar pregnancy

Some abnormal cells may be left in your womb after treatment. These usually go away on their own within a few months, but further treatment may sometimes be needed to remove them.

To see if you might need further treatment, you'll be asked to have regular blood or urine tests to measure the level of the hormone hCG (human chorionic gonadotrophin).

The amount of this hormone in your body increases during pregnancy. If it doesn't go down after treatment for a molar pregnancy, it might mean some abnormal cells are left in your womb.

Most women need to have regular blood or urine tests for around six months after treatment.

See further problems after a molar pregnancy for information about what happens if your hCG level doesn't go down.

Sex, pregnancy and contraception after a molar pregnancy

You can have sex as soon as you feel physically and emotionally ready. If you have any bleeding after your treatment, don't have sex until this stops.

Having a molar pregnancy doesn't affect your chances of getting pregnant again, and the risk of having another molar pregnancy is small (about 1 in 80).

It's best not to try for a baby until your after-treatment monitoring has finished, in case you need further treatment to remove any cells left in your womb.

Use contraception until your doctors say it's safe to get pregnant again. You can use any type except implants that go in the womb, which should only be used once your hCG level has returned to normal.

Further treatment after a molar pregnancy

In a few cases, abnormal cells left in the womb after treatment don't go away on their own. This is called persistent trophoblastic disease (PTD).

The chances of this happening are about 1 in 7 (15%) if you had a complete mole and about 1 in 200 (0.5%) if you had a partial mole.

PTD can be serious because the abnormal cells can regrow or spread to other parts of the body, similar to cancer, if it's not treated.

Treatment involves taking medication to kill the abnormal cells (chemotherapy) for a few months. Most women have a combination of:

• injections of a medicine called methotrexate
• tablets of a medicine called folinic acid

With treatment, almost 100% of women are cured.

You can usually get pregnant after treatment if you wish, but you will be advised not to try for at least a year because there's a chance (about 1 in 30) PTD could come back during this time. 

Cause of molar pregnancies

A molar pregnancy isn't caused by anything you or your partner does.

It happens if there amount of genetic material in a fertilised egg isn't right – for example, if an egg containing no genetic information is fertilised by a sperm, or a normal egg is fertilised by two sperm. 

It's unclear why this happens, but the following things can increase the risk:

• Age – molar pregnancies are more common in teenage women and women over 45.
• Ethnicity – molar pregnancies are about twice as common in women of Asian origin.
• Previous molar pregnancy – if you've had a molar pregnancy before, your chance of having another one is about 1 in 80, compared with 1 in 600 for women who haven't had one before. If you've had two or more molar pregnancies, your risk of having another is around 1 in 5.

More information and support

It can take time to recover emotionally from a molar pregnancy.

You may find it helpful to:

• Talk to your partner, family or friends about how you feel.
• Ask your care team what support is available. They may refer you to a counsellor who specialises in support for people affected by molar pregnancy.
• Contact a support group, such as the Molar Pregnancy Support Group or MyMolarPregnancy.com. They may be able to put you in touch with other people in a similar situation.
• Read advice about coping with grief and loss.

Specialist NHS services

There are two NHS centres in England that specialise in the care of women with molar pregnancies and persistent trophoblastic disease:

• Charing Cross Hospital Trophoblast Disease Service, London
• Sheffield Trophoblastic Disease Centre

There is also a Scottish Hydatidiform Mole Follow-up Service in Dundee.