A molar pregnancy is a pregnancy that has not been successful, and means that a baby will not develop.

What happens

In a normal pregnancy, the placenta provides nourishment to a developing baby and removes waste products. The placenta is made up of millions of cells known as trophoblastic cells.

In a molar pregnancy, these cells behave abnormally as soon as the egg has been fertilised by the sperm. This results in a mass of abnormal cells rapidly growing within the womb instead of a normally developing baby. This mass of cells is referred to as a "mole".

Other terms for a molar pregnancy are gestational trophoblastic tumour, trophoblastic disease and hydatidiform mole.

Removing the mole

A mole is classed as a benign growth, which means it is not cancerous. However, it must be removed surgically. This is done under the care of a gynaecologist.

The operation to remove the mole is called dilatation and curettage, which involves removing the lining of the womb.

How common is it?

It is uncommon: about one in every 700-800 pregnant women will develop a molar pregnancy.

Symptoms and diagnosis

Some women will develop abnormal symptoms of pregnancy. The most likely symptom of a molar pregnancy is vaginal bleeding. Your doctor will usually be able to identify a molar pregnancy during the first ultrasound scan, at 10-16 weeks of pregnancy.

A partial vs a complete mole

A complete molar pregnancy is a mass of rapidly growing cells that does not contain a foetus (unborn baby). It develops when there is only genetic material from the father, and the mother's genetic material is missing.

A partial mole occurs when there is genetic material from both the father and mother, but there are two sets of material from the father. A foetus may be visible on an early ultrasound, but this is abnormal and will not survive beyond the first three months of pregnancy.