Diagnosing molar pregnancy

In a molar pregnancy the fertilisation of the egg by the sperm goes wrong. This creates abnormal cells or clusters of water filled sacs inside the womb. 

Molar pregnancy is usually diagnosed during routine pregnancy tests and scans. But you may also have a number of tests if you have symptoms of a molar pregnancy. 

Blood and urine tests

When you are pregnant, the placenta produces a hormone called human chorionic gonadotrophin (hCG). It helps the baby to develop. It isn’t normally present in women who aren’t pregnant. The placenta releases hCG into your bloodstream and your body gets rid of the rest in your urine. 

Molar pregnancies also produce hCG and the levels can be much higher than normal. So measuring the levels of hCG in your blood and urine can help to diagnose a molar pregnancy.

Abdominal ultrasound

Ultrasound scans use high frequency sound waves to create a picture of a part of your body. You usually have the scan in the hospital ultrasound department by a sonographer. A sonographer is a trained professional who specialises in ultrasound scanning. The scan can take up to 45 minutes.

Women usually have a routine ultrasound of their tummy in the 12th week of their pregnancy to look for any abnormalities. This means that most molar pregnancies are picked up at a very early stage.

Molar pregnancies can show a characteristic 'snowstorm appearance' on the scan. There will also be no foetal tissue or only partial tissue. If the scan shows a molar pregnancy your healthcare team will tell you as soon as they can.

Abdominal ultrasound scans are a good way of diagnosing a complete molar pregnancy. But they are not as good at picking up partial molar pregnancies. Partial molar pregnancies are still likely to be picked up by other routine tests, such as blood tests. 

Transvaginal ultrasound

If you have symptoms before your routine scan, your doctor might refer you for a transvaginal ultrasound. 

A transvaginal ultrasound is an internal scan. A slim ultrasound probe is put just inside your vagina to get a more detailed picture. This doesn’t hurt but it may feel slightly uncomfortable as they move the probe around.

You usually have the scan in the hospital ultrasound department or early pregnancy unit.  A sonographer or specially trained nurse will do the scan. If the scan shows a molar pregnancy your healthcare team will tell you as soon as they can.

Diagnosis after miscarriage or abortion

You might be asked to give a urine sample 3 weeks after a miscarriage or abortion. This is to check that your hCG level has gone down.

If you’ve had a miscarriage in hospital or an abortion, a doctor usually examines the placental and foetal tissue in the laboratory. These checks can pick up the abnormal cells of a molar pregnancy.

If you have a molar pregnancy

Your healthcare team will tell you if they see a molar pregnancy. This can be a shock and can be very upsetting.

Your doctor or nurse can support you and let you know about counselling or organisations that can help you. 

You will need to have treatment to remove the molar pregnancy from the womb.

Cancer Research UK nurses