Hydatidiform Mole

Understanding conception

Most cells in the body have two copies of your individual genetic code. A complete genetic code is needed for a baby to develop. This code determines what we look like, how our body functions, whether we are male or female and sometimes even whether we will get certain diseases. However, the reproductive cells (ova in women and sperm in men) have only one copy of this code.

In normal conception, one sperm which contains a single copy of the father’s genetic code fertilises one egg which contains a single copy of the mother’s genetic code. This results in a fertilised egg or embryo with a complete set of genetic material.

What is a hydatidiform mole?

A hydatidiform mole (molar pregnancy) is a growing mass of tissue inside the womb (uterus) that will not develop into a baby. It is the result of abnormal conception. It may be either complete or partial. A complete mole develops when there are two copies of the father’s genetic code and no copies of the mother’s genetic code. This can occur when sperm fertilise an empty ovum or when the ovum loses its genetic code at the time of conception. There is no tissue resembling a foetus (an unborn baby) at all.

A partial mole occurs when there are two copies of the father’s genetic code and one copy of the mother’s genetic code. This is usually due to two sperm fertilising one normal ovum. In this case, some foetal tissue and foetal red blood cells are present.

Partial and complete moles will not produce a live baby. They are non viable pregnancies.

How common is a hydatidiform mole?

Hydatidiform mole is rare in the UK. There is about 1 molar pregnancy for every 714 live births. This works out to be less than 1000 moles per year. A hydatidiform mole can occur to any woman of child bearing age but women who are under 16 and over 40 are at a higher risk. Women of Far Eastern and Asian backgrounds are also more likely to have a molar pregnancy.

What are the symptoms of a hydatidiform mole?

• Bleeding. You may have vaginal bleeding early in the pregnancy.
• No symptoms. About 4 in 10 women with a hydatidiform mole have no symptoms.
• Pregnancy symptoms. You may notice that you feel bigger than expected for the number of weeks you are pregnant.
• Rare symptoms. Very rarely, you may have problems with high blood pressure, very bad nausea and vomiting (hyperemesis gravidarum) or an overactive thyroid.

How is a hydatidiform mole diagnosed?

If you develop bleeding in early pregnancy, your doctor will usually arrange an ultrasound scan. The picture on the ultrasound scan can be quite characteristic of a hydatidiform mole and may give a clear diagnosis. However, in early pregnancy, the ultrasound picture may look like a miscarriage. In this case, the definite diagnosis is made when the pregnancy is removed and examined under a microscope (see below).

If you do not have bleeding or other symptoms, the diagnosis is usually made when you have a routine pregnancy ultrasound scan.

What is the treatment for a hydatidiform mole?

If you have a hydatidiform mole, you will need to have it removed. This is done by a specialist in hospital. You will be given an anaesthetic. A small tube will be passed into the uterus (womb) through the cervix (the opening of the uterus) and the abnormal tissue is removed by suction. The tissue is then sent off to the laboratory for further examination under the microscope.

Are there any complications?

If you have a hydatidiform mole, it is very important to be registered with one of the three specialist centres in the UK. Your gynaecologist should arrange this for you. These centres will arrange follow up. This is necessary because there is a small risk that you can develop a rare cancer which can spread (metastasise) to other parts of your body.

About 1 in 200 women with partial moles and 15 in 100 women with complete moles will develop a cancer called persistent gestational trophoblastic neoplasia (GTN). This cancer can be detected by a blood test. The blood test checks for the pregnancy hormone human chorionic gonadotrophin (HCG). This is the hormone that is tested in standard pregnancy tests. When you are first diagnosed with a hydatidiform mole, your HCG level will be raised as it is in normal pregnancy. When the hydatidiform mole is treated, the HCG level will return to a normal non-pregnant level and will remain at this level. If you develop persistent GTN, the HCG level will rise. So, this blood test is a good way to check for the development of cancer. Your specialist centre will advise you on how often to have this test done.

If you do develop persistent GTN you will need further treatment. The treatment depends on how advanced the cancer is. For example, whether the cancer has spread to other parts of the body or not. Treatment involves injections of different medications (chemotherapy) such as methotrexate, etoposide and dactinomycin.

What is the outlook (prognosis)?

Most women who have a hydatidiform mole have an excellent outlook. The risk of developing persistent GTN from any type of mole is about 1 in 10. This means that about 1 in 10 women who have a hydatidiform mole will develop persistent GTN. In those who develop persistent GTN, about 97 in 100 are completely cured.

After a hydatidiform mole, you will be advised not to fall pregnant until your HCG levels have been normal for six months. If you have had persistent GTN, you will be advised not to fall pregnant until the levels have been normal for 12 months.

Only two women in 100 who fall pregnant after previously having a hydatidiform mole will develop another hydatidiform mole.

Once your HCG levels have returned to normal, it is safe to use the contraceptive pill and HRT, if needed.

Further Information

The Gestational Trophoblastic Tumour Screening Unit
Dept. Medical Oncology, Charing Cross Hospital, Fulham Palace Road, London, W6 8RF
Web: www.hmole-chorio.org.uk