What is a molar pregnancy?
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What is a molar pregnancy?
Molar pregnancy is a type of gestational trophoblastic tumour. It happens when the normal fertilisation of an egg goes wrong. This leads to the growth of clusters of fluid filled sacs inside the womb. Most molar pregnancies are not cancerous (they are benign). Even though they can spread beyond the womb, they are curable. In the UK, about 1 in 1,000 women who become pregnant (0.1%) will develop a molar pregnancy.
Complete and partial moles
If you have a ‘complete mole’ no parts of a baby (foetal tissue) form. Some women who have a complete molar pregnancy will need to have chemotherapy. A small number of women with a complete mole go on to develop a cancerous gestational tumour (choriocarcinoma).
If you have a partial mole there may be some foetal tissue in the womb, alongside the molar tissue. It is important to understand that the foetal tissue cannot develop into a baby. It is very unusual that women with a partial mole will go on to need chemotherapy or develop a cancerous gestational tumour.
Very rarely a twin pregnancy will show a developing baby and a molar pregnancy. This is a very difficult situation. You will need to talk to your doctor about the risks and the choices available to you.
Persistent trophoblastic disease is when you have had treatment to remove a molar pregnancy but still have some disease left.
You can view and print the quick guides for all the pages in the About molar pregnancy section.
A molar pregnancy occurs when the fertilisation of the egg by the sperm goes wrong and leads to the growth of abnormal cells or clusters of water filled sacs inside the womb. This condition is the most common of a group of conditions known as gestational trophoblastic tumours. Molar pregnancies used to be called hydatidiform mole but now most people call them molar pregnancies. Most molar pregnancies are benign (not cancerous). They can spread beyond the womb in some women, but are still curable.
Molar pregnancies are rare but they are the most common type of gestational trophoblastic tumour. In the UK, about 1 in 1,000 women who become pregnant will develop a molar pregnancy. In Asian women, molar pregnancies are twice as common.
Molar pregnancies can either be complete or partial. There is information about both types further down this page.
If you have a ‘complete mole’ no parts of a baby (foetal tissue) are formed as part of the pregnancy. The molar tissue is usually removed with surgery. In around 5 or 8 out of 100 women who have a complete molar pregnancy the molar tissue begins to grow into the deeper tissues of the womb. They will need to have chemotherapy after the molar tissue is removed. A small number of women with a complete mole go on to develop a cancerous gestational tumour (choriocarcinoma).
If you have a partial mole there may be some foetal tissue in the womb, alongside the molar tissue. It is important to understand that the foetal tissue cannot develop into a baby, although on ultrasound it may look like a foetus. The molar tissue needs to be surgically removed. Most women with a partial mole do not then need to have any further treatment. Overall, fewer than 1 in 200 (0.5%) need chemotherapy treatment after the molar tissue has been removed. It is very rare for women to develop a cancerous gestational tumour after they have had a partial mole.
Very rarely a twin pregnancy will show a normal developing baby and a molar pregnancy at the same time. This happens in fewer than 1 in 100 cases of GTT (less than 1%). The risk of developing persistent trophoblastic disease is higher in this situation. For many women it is possible for the pregnancy to continue. Reports show that in about 25 to 40 out of every 100 of these cases (25 to 40%) the healthy baby can be delivered and survives. But if you have complications you may not be able to go ahead with the pregnancy. This is obviously a very difficult situation. Your doctor will tell you about the risks involved. They may refer you to one of the national molar pregnancy treatment centres for advice. You may also have counselling so that you can think through any choices you might have before you make a decision.
Persistent trophoblasic disease is when you have had treatment to remove a molar pregnancy but still have some molar tissue left and it grows and forms a new tumour. This occurs in about 1 in 10 women (10%) after a molar pregnancy. If it is not treated it can grow quickly and cause a number of medical problems. Most women with persistent trophoblastic disease need to have chemotherapy treatment. There is more information about persistent trophoblastic disease and its treatment in this section of CancerHelp UK.
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