Molar pregnancy: Frequently asked questions

What does this mean for me?

A molar pregnancy is also known as a Hydatidiform mole or Gestational Trophoblastic Disease. In a molar pregnancy the placental cells grow abnormally. Molar pregnancies occur sporadically as a result of imbalance in the number of chromosomes. Because of this imbalance it is not possible for a healthy pregnancy to develop. There are two types of molar pregnancy.

1. Partial mole

This is where two sperms have fertilised an egg and there are three sets of chromosomes instead of the normal two.

2. Complete mole

This is where one sperm (or sometimes two) fertilises an empty egg (containing no genetic material).

How is it diagnosed?

The diagnosis of a molar pregnancy is often made after a miscarriage, when the pregnancy tissue has been looked under the microscope by a hospital laboratory. There are specific criteria used by the laboratory to determine if the pregnancy was partial and complete molar pregnancy. Sometimes there may be a suspicion of this diagnosis on an ultrasound scan but it can only be confirmed after a detailed examination under the microscope.

What happens next?

When there is a suspicion of a molar pregnancy, an operation to remove the pregnancy tissue from the womb will be required, as this is not a healthy pregnancy. This operation is usually done under general anaesthetic and involves a small suction tube being passed through the vagina and cervix (the neck of your womb) to remove the pregnancy. The pregnancy tissue will be sent to the laboratory for detailed assessment.

If a molar pregnancy is confirmed, you will need serial blood tests to confirm that the pregnancy hormone (βHCG) reduce to negative levels. This is important as there is a small risk that some of the abnormal pregnancy cells could develop into a more severe form of molar pregnancy (see below).

You will be referred to the nearest highly specialist centre near you, which are based in London, Sheffield or Dundee who will be in charge of this follow up over several weeks and months. This follow-up is very important because in some cases the molar pregnancy keeps growing and can occasionally develop into a rare form of cancer called Gestational Trophoblastic Neoplasia. This is not common and if it does occur treatment with chemotherapy is associated with extremely high cure rates (98-100% cure rate).

It is very important that you do not fall pregnant until your follow-up has been complete. Nearly all methods of contraception are safe to use, but an intrauterine device such as a coil is not recommended until your betaHCG becomes negative. We recommend you discuss the most appropriate type of contraception further with your doctor. The risk of molar pregnancy happening again in future pregnancy is low and is around 1 in 100 women.