Molar pregnancy (hydatidiform mole)

Molar pregnancy can be a very distressing experience. It’s also a type of pregnancy loss that most people have never heard of, so it can be difficult to get the information and support you need.

This section of our website aims tell you something about

You can also find more detailed information in our leaflet on molar pregnancy.

We hope this will help at what can be a very difficult time.

What is a molar pregnancy?

A molar pregnancy (also called a hydatidiform mole) is one where an abnormal fertilised egg implants in the uterus (womb). The cells that should become the placenta grow far too quickly and take over the space where the embryo would normally develop.

The term ‘hydatidiform mole’ means a fluid-filled mass of cells. The word mole means a mass of cells; and hydatid means containing fluid-filled sacs or cysts.

Those cells are called trophoblasts. That’s why molar pregnancy is sometimes also called ‘trophoblastic disease’.

About one in 600 pregnancy pregnancies is molar, so it’s quite rare.

Molar pregnancies might be partial or complete.

In a partial mole, two sperm fertilise the egg instead of one. There is too much genetic material for the baby to be able to develop.

In a complete mole, one (or even two) sperm fertilises an egg cell that has no genetic material inside. There are not enough of the right chromosomes for the baby to be able to develop.

In a very small number of cases, molar cells burrow more deeply into the uterus than they should. These cells can become cancerous and spread into other parts of the body. This is called invasive mole. If invasive mole is not treated, it can develop into choriocarcinoma, which is a form of cancer. Fortunately it is a cancer with a cure rate of almost 100%.

Can a molar pregnancy survive?

No. Molar pregnancies all have the wrong number or balance of chromosomes and they can’t survive.

You can read about causes, symptoms and diagnosis of molar pregnancy here.