Gestational trophoblastic disease covers several pregnancy conditions that involve the placental tissue growing rapidly and occasionally becoming cancerous. The abnormal proliferation (or growth) of the placental tissue is called a mole, and the pregnancy is known as a molar pregnancy. Most molar pregnancies are diagnosed after a curette for a miscarriage or when bleeding early in pregnancy prompts an ultrasound scan.
The term gestational trophoblastic disease covers several pregnancy conditions that involve the placental (afterbirth) tissue turning cancerous or cancer-like. In Australia, this cancer occurs in one in every 600 to 1000 pregnancies.
The main symptom of gestational trophoblastic disease is abnormal bleeding in pregnancy, but often it is diagnosed after a curette for a miscarriage. Nowadays, the condition tends to be diagnosed early, so sufferers rarely present with violent morning sickness, which was previously considered a common symptom.
The tumour is called a mole, and the pregnancy is known as a molar pregnancy, because the placental tissue burrows into the wall of the uterus. In most cases, the woman miscarries and passes the mole from her body, or it is removed with a dilatation and curettage (D&C).
The cause of gestational trophoblastic disease is unknown, but risk factors include maternal age. Women aged less than 20 years or more than 40 years are most susceptible.
Symptoms of molar pregnancy
The symptoms of gestational trophoblastic disease can include:
- Vaginal bleeding during pregnancy
- The uterus being either too big or, less commonly, too small for the gestational age of the foetus
- No foetal movement
- No foetal heartbeat
- Extremely severe morning sickness
- An ultrasound that reveals a typical “snowstorm” appearance due to the abnormal placenta and lack of foetal parts.
Risk factors for molar pregnancy
The cause of gestational trophoblastic disease is unknown, but risk factors include:
- Maternal age of less than 20 or more than 40 years
- Race, since Asian women are at increased risk
- Dietary deficiencies including lack of folate, beta-carotene or protein
- Prior history of gestational trophoblastic disease. The recurrence rate is one in 100.
Formation of a molar pregnancy
The cells of the developing foetus split into two broad groups – one group becomes the body and the other becomes the placenta. The placenta has millions of tiny finger-like projections (villi) that are designed to ‘dig in’ to the womb wall and tap into the mother’s blood supply.
In gestational trophoblastic disease, the foetus doesn’t grow, but the placenta grows abnormally. The villi swell and look like little blisters. These blisters are called a hydatidiform (meaning grape-like) mole, and the pregnancy is called a molar pregnancy.
The woman experiences the symptoms of pregnancy because the placenta continues to make the pregnancy hormone human chorionic gonadotrophin (HCG). However, the level of HCG is usually higher than normal, which explains why severe and occasionally violent morning sickness can occur. In some cases, the morning sickness is so severe that hospitalisation is needed.
Complications of molar pregnancy
The hydatidiform mole can cause a wide range of complications including:
- Ovarian cysts
- Breathlessness (when it spreads to the lungs)
- Pre-eclampsia (toxaemia of pregnancy), involving high levels of certain substances in the blood that raise blood pressure and affect the kidneys and (sometimes) liver function
- Recurring gestational trophoblastic disease
- Excess thyroid hormone production, which causes heart palpitations and other thyroid hormone effects.
- Regrowth – persistent mole regrowth of the placental tissue
- Invasive mole – the tumour spreads into the wall of the uterus
- Metastatic mole – molar cells migrate to other organs of the body and cause secondary tumours. The lungs are common sites for metastatic moles
- Gestational choriocarcinoma – a rapidly spreading type of cancer that can travel to any part of the body via the blood vessels or lymphatic system.
Diagnosis of molar pregnancy
Gestational trophoblastic disease can be hard to diagnose because:
- A woman who experiences a miscarriage will not know whether or not she passed a hydatidiform mole unless the aborted tissue is examined in a laboratory
- If recent pregnancy, labour and birth were normal, there is often no reason to suspect gestational trophoblastic disease until symptoms become apparent.
- Medical history, which could include current pregnancy or recent childbirth, miscarriage or abortion
- Physical examination
- Blood test to check for high levels of the pregnancy hormone HCG
- Ultrasound (the most common method of diagnosis)
- Other scans including x-rays, computed tomography (CT) or magnetic resonance imaging (MRI) if it is thought the cancer may have spread to other areas of the body.
Treatment of molar pregnancy
Promptly treated, molar pregnancies are curable in 100 per cent of cases. Treatment options depend on various factors, including whether or not the tumour has spread to other areas of the body, but could include:
- D&C – the cervix is gently opened and the uterine contents are removed
- Hysterectomy – if a woman doesn’t want any more children, the surgical removal of her uterus may be recommended
- Chemotherapy – if the hormone level does not fall or continues to rise, or if spread has occurred and the mole is therefore behaving like a cancer, chemotherapy will be needed.
Molar pregnancy can recur
Gestational trophoblastic disease can recur, so regular check-ups are needed. The primary test for the disease is the blood test for HCG or a 24-hour collection of urine to measure HCG levels.
If the HCG levels remain high, then the mole may have returned. It is important to strictly avoid pregnancy for at least the first year or so following treatment, because a normal pregnancy will produce HCG and make the blood test for gestational trophoblastic disease ineffective.
In Victoria, all women with a hydatidiform mole pregnancy are registered at the Royal Women’s Hospital. Follow up is monitored and support is available for women with this diagnosis. In other states in Australia, care is usually provided by a specialist gynaecologist.
Where to get help
- Your doctor
- Hydatidiform Mole Registry, Royal Women’s Hospital Tel. (03) 8345 2620
- Women’s health clinic
- Family Planning Victoria Tel. (03) 9257 0100
- Cancer Council Victoria Tel. 13 11 20
Things to remember
- Gestational trophoblastic disease is a term covering pregnancy conditions, notably molar pregnancy, that involve the foetal tissue turning cancerous or cancer-like.
- Molar pregnancy is usually diagnosed in early pregnancy when bleeding occurs.
- The cause of molar pregnancy is unknown, but risk factors include maternal age of less than 20 years or more than 40 years.
- Gestational trophoblastic disease can recur, so regular check-ups are needed.
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Last reviewed: June 2011
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