Hydatidiform Mole

hydatiform mole

A hydatidiform mole is a growing mass of tissue inside your uterus (womb) that will not develop into a baby. It is the result of abnormal conception. It may cause bleeding in early pregnancy and is usually suspected on an early pregnancy ultrasound scan. It needs to be removed and most women can expect a full recovery. However, close follow-up is needed after a hydatidiform mole because there is a small chance of developing a type of cancer. If a cancer does develop, effective treatment is available and most women are completely cured.

Understanding conception

Chromosomes are found in the nucleus (the centre) of the cells in your body. They carry genetic information in the form of genes. Most of the cells in your body contain 46 chromosomes arranged in 23 pairs. One chromosome from each pair is inherited from your mother and the other is inherited from your father. These 46 chromosomes make up your genetic code.

This code determines what you look like, how your body functions, whether you are male or female and sometimes even whether you will get certain diseases.
However, the reproductive cells (eggs, or ova, in women and sperm in men) only have 23 chromosomes. This is so that, when a sperm fertilises an egg during normal conception, the child that is produced has 46 chromosomes in each cell, 23 from their mother and 23 from their father.

The fertilised egg, or ovum, has a complete set of genetic material.

After fertilisation, some cells from the fertilised ovum (called the trophoblast cells) develop into the placenta and membranes that form around the developing baby and some cells develop into the embryo from which the baby grows. As the placenta develops, the trophoblast cells grow into and attach to the lining of the uterus (womb), allowing the pregnancy to implant in the uterus.

What is a hydatidiform mole?

A hydatidiform mole is a growing mass of tissue inside the uterus that will not develop into a baby. It is the result of abnormal conception. A hydatidiform mole may be either complete or partial.

Sometimes, during conception, a sperm fertilisesan 'empty' ovum (an ovum not carrying any chromosomes or genetic material). Under normal circumstances, the fertilised empty ovum would die and not implant in the uterus. But rarely, the ovum doesn't die and implantation takes place. The trophoblast cells grow and develop as a disorganised mass of tissue but the embryo does not develop. This is a complete hydatidiform mole. There is no tissue resembling a fetus (an unborn baby) at all.

A partial hydatidiform mole is also possible if conception doesn't take place normally. It is usually due to two sperm fertilising one normal ovum (which should not usually happen). This means that there is too much genetic material present. There is also too much trophoblastic tissue. The growth of the trophoblastic tissue overtakes the growth of any fetal tissue and the fetus does not develop normally.

Partial and complete hydatidiform moles will not produce a live baby. They are nonviable pregnancies. A pregnancy that results in a hydatidiform mole is called a molar pregnancy.
A hydatidiform mole is part of a group of disorders called gestational trophoblastic disease (GTD). Partial and complete hydatidiform moles are benign (noncancerous) forms of GTD. However, there is a risk that a hydatidiform mole can develop into a malignant (or cancerous) type of GTD, known as gestational trophoblastic neoplasia (GTN). This is described below.

How common is a hydatidiform mole?

There is about 1 molar pregnancy for every 714 live births. Any woman of childbearing age can develop a molar pregnancy but women who are aged under 16 and over 40 have a higher risk. For some reason, women of Asian backgrounds are also more likely to have a molar pregnancy.

What are the symptoms of a hydatidiform mole?

Women with a hydatidiform mole usually have higher than average levels of the pregnancy hormone human chorionic gonadotrophin (hCG) compared with women with a normal pregnancy. This hormone is produced by the trophoblastic tissue. It is the hormone that is detected in a standard pregnancy test. The high levels of hCG are because there is an excessive amount of trophoblastic tissue with a hydatidiform mole. The high hCG levels are responsible for some of the symptoms.

Pregnancy symptoms. You may have signs of pregnancy, including no periods, nausea or vomiting, breast tenderness, etc. You may notice that you feel bigger than expected for the number of weeks you are pregnant. This is because a molar pregnancy grows more quickly than a normal pregnancy would due to the abnormally developing trophoblastic tissue.
Bleeding. You may have vaginal bleeding early in the pregnancy. This is the most common symptom. Many women suspect that they are having a miscarriage.

No symptoms. Some women with a hydatidiform mole have no symptoms. The molar pregnancy is diagnosed after a routine pregnancy ultrasound scan (see below).
Rare symptoms. Rarely, you may have problems with high blood pressure, very bad nausea and vomiting (hyperemesis gravidarum) or symptoms of an overactive thyroid gland may develop.

How is a hydatidiform mole diagnosed?

If you develop bleeding in early pregnancy, your doctor will usually arrange an ultrasound scan. Sometimes, the picture on the ultrasound scan can be quite characteristic if you have a hydatidiform mole. However, at other times the ultrasound picture may just look like a miscarriage. If your doctor suspects that you have a hydatidiform mole, they may also suggest a blood test to check your levels of hCG. Higher than normal levels can help with the diagnosis.

If you have an ultrasound picture that looks like a miscarriage and higher than normal hCG levels, the definite diagnosis of hydatidiform mole is made when the pregnancy is removed and examined under a microscope.

If you do not have bleeding or other symptoms, the diagnosis of hydatidiform mole is usually suspected when you have a routine pregnancy ultrasound scan. The further through the pregnancy you are, the more characteristic the ultrasound picture of a molar pregnancy becomes.

How do you treat hydatidiform mole?

Hydatiform moles should be removed. This means having a small operation. This is done by a gynaecology specialist in hospital. You will be given an anaesthetic. In most cases, a small tube is passed into your uterus through your cervix (the opening of your uterus) and the abnormal tissue is removed by suction. The tissue is then sent off to the laboratory for examination under the microscope.

What follow-up do I need after a hydatidiform mole?

As mentioned above, there is a small risk that you can develop GTN after a hydatidiform mole. There is a risk that this can spread (metastasise) to other parts of your body including your lung, liver or brain. Therefore, you need close follow-up after a hydatidiform mole to monitor for this.

When you are first diagnosed with a hydatidiform mole, your hCG level will be raised. As mentioned above, levels are usually higher than they would be in a normal pregnancy. When the hydatidiform mole is treated (removed), the hCG level will usually return to a normal, nonpregnant level and should remain at this level. If you develop GTN, the hCG level can remain elevated or continue to rise further. So, this blood test is a good way to check for the possible development of GTN.

Is treatment possible if I develop gestational trophoblastic neoplasia?

Yes. Treatment is possible and is effective in most cases.

About 1 in 200 women with partial moles and 15 in 100 women with complete moles will need treatment because hCG levels are not returning to normal. The exact treatment given depends on things such as your hCG levels, whether there is spread to other parts of the body, etc. Treatment involves injections of different medications (chemotherapy) such as methotrexate, etoposide and dactinomycin. Treatment is continued until your hCG level has returned to normal, and then for some weeks afterwards.

What is the outlook (prognosis)?

Most women who have a hydatidiform mole have an excellent outlook. As mentioned above, about 1 in 200 women with partial moles and 15 in 100 women with complete moles will need treatment for GTN. In those who develop GTN, at least 98 in 100 are completely cured.

Once your hCG levels have returned to normal, it is safe to use the contraceptive pill or an intrauterine contraceptive device (IUCD) if needed. But, until your hCG levels return to normal, you should use a barrier method of contraception such as condoms. HRT can also be used once your hCG levels have returned to normal.

When is it safe to try for another baby?

Your specialist will advise you when it is safe to try for another baby if you have had a hydatidiform mole or GTN. Less than 2 in 100 women who fall pregnant after previously having a hydatidiform mole will develop another hydatidiform mole in a subsequent pregnancy.

Rarely, gestational trophoblastic disease can be 'reactivated' after a future pregnancy even several years later. For this reason, your hCG levels should be monitored for a time after any pregnancy ends (be it a normal pregnancy, a miscarriage, a termination, etc). You or your gynaecologist should contact the specialist centre that you are registered with to arrange this.

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