A hydatidiform mole brings alarming talk of tumours and cancer. Dr Howard Lee explains the diagnosis, treatment and prognosis

It is a terrible shock when you go for your first ultrasound and instead of regular heartbeats showing up on the screen, you're told that your baby has stopped growing and that you may have a 'molar pregnancy'.

But this is often how women discover that they're suffering from this rare complication, which affects 1 in 1,000 pregnancies. It is not clear why hydatidiform moles develop in the womb, but we do know that a previous miscarriage doubles the chance and that the risk also increases with age.

What is a molar pregnancy?

It occurs when the developing tissue responsible for the placenta (afterbirth) develops abnormally and overgrows to form a hydatidiform mole.

The placenta is made up of millions of cells called trophoblastic cells and this overgrowth is often referred to as 'trophoblastic disease'.

The hydatidiform mole itself is usually harmless and a cancerous change is quite rare. However, if the condition is not treated, it can continue to grow, burying itself into the surrounding organs.

It can also spread through the bloodstream to other parts of the body, including the lungs, liver, brain, spleen and kidneys.

Types of trophoblastic disease

Hydatidiform mole where the abnormal placental tissue growth is benign but capable of spreading if not treated.

There are two types:

• partial mole where only part of a normal placenta shows overgrowth - any baby that is present is not developing normally
• complete mole where the entire placenta, which is growing rapidly, is abnormal, and there is no baby present

Persistent trophoblastic disease where part of a previous mole remains after treatment. Even a tiny piece of mole in any part of the body can grow rapidly and cause problems.

Choriocarcinoma is a very rare cancer, which is curable. In this case, the placenta develops a malignancy, which can spread throughout the body. It can occur in a molar pregnancy, a miscarriage, an ectopic pregnancy, and even following an otherwise normal pregnancy.

Signs of a molar pregnancy

• vaginal bleeding
• the womb grows more quickly than normal
• no foetal movements
• leaking from the vagina of material that looks like a cluster of grapes
• excessive vomiting in early pregnancy due to a higher level of the pregnancy hormone hCG (human Chorionic Gonadotrophin) than normal

Diagnosing a molar pregnancy

1. Ultrasound scanning enables early diagnosis of molar pregnancy - especially in the case of a complete mole. Incomplete moles can be more difficult to identify if some parts of the foetus are present - if there is any uncertainty a repeat scan will be arranged.

In a Twin pregnancy where one is a partial molar pregnancy, the pregnancy is usually allowed to go ahead. It can also proceed if there's a complete mole alongside a normal pregnancy, but couples will be counselled about the risks involved:

• reduced live birth rate of 25 per cent
• risk of haemorrhage or pre-eclampsia
• subsequent need for chemotherapy in about 20 per cent of cases

2. Laboratory examination and testing after a miscarriage, termination or an ectopic pregnancy, the placenta is always examined by a pathologist.

In molar pregnancies the abnormal overgrowth of the placenta leads to excessive production of the pregnancy hormone human Chorionic Gonadotrophin (hCG).

A simple blood or urine sample can determine levels of hCG, and:

• help to diagnose a molar pregnancy
• indicate when the disease is cured - as it improves, levels fall, and when there's no disease in the body, the level of hCG in the blood or urine is virtually zero

Treating a molar pregnancy

Dilatation and Curettage (D&C or 'scrape') is carried out to remove as much of the placenta from the womb as possible.

It may be necessary to repeat this procedure because even a tiny amount of mole left in the body can grow and spread. In the majority of cases this operation does cure the disease. Chemotherapy is necessary in about 6-10 per cent of cases with the following symptoms:

• hCG levels have risen for two weeks or more
• examination of tissue has shown choriocarcinoma
• the disease has spread to other areas
• hCG levels have increased after a normal value

What are the chances of having another baby?

This is a highly curable disease and the prognosis is good even when it has spread to other organs.

If the disease is limited to the womb cavity, it is 100 per cent curable, and less than 1 in every 10 women will require chemotherapy.

But if a woman gets pregnant too soon after the molar pregnancy, the risk of a recurrence is increased and the mole can reactivate. Because the disease is assessed by measuring the levels of hCG hormone - usually only seen in pregnancy - it is important to avoid getting pregnant during the follow-up period.

For the same reason, any hormone treatments, including the Pill, should not be used for at least three months after the 'all-clear' is given.

Your doctor will continue to monitor your condition for between six months and two years, depending on the type of mole.

You may feel fine during this time but it is really important to continue with the monitoring process - any high or rising levels of hCG in your blood will warrant further investigation and treatment.

Most importantly, after the disease has been cured, you should be able to have a normal, healthy pregnancy and remain free from the disease for the rest of your life.

We are fortunate in the UK to have an effective registration and treatment programme for molar pregnancies.

Charing Cross Hospital in London, Ninewells Hospital in Dundee and Weston Park Hospital in Sheffield are the three centres established in the UK to screen for gestational trophoblastic tumours, and they provide information and support for patients undergoing treatment.

Here are two useful websites which have further information: