The term gestational trophoblastic disease (GTD) covers several pregnancy conditions that involve the placental tissue turning cancerous or cancer-like. In Australia, this condition occurs in one in every 600 to 1000 pregnancies.
The main types of GTD are hydatidiform mole (also known as molar pregnancy; this is the most common form) and gestational trophoblastic neoplasia (also known as persistent gestational trophoblastic disease).
In a molar pregnancy the cancerous or cancer-like placental tissue (known as a mole) 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 surgical procedure called a dilatation and curettage (D&C). If treated early, molar pregnancy is 100 per cent curable.
The cause of molar pregnancy is unknown, but a key risk factor is maternal age. Women aged less than 20 years or more than 40 years are most susceptible.
Symptoms of molar pregnancy
The symptoms of molar pregnancy can include:
- vaginal bleeding during pregnancy
- abnormal appearance of the placenta at the first ultrasound (called a ‘snowstorm’ pattern).
More rarely, when a diagnosis is not made until later gestation, symptoms include:
- a uterus larger than expected
- no foetal movement
- no foetal heartbeat
- extremely severe morning sickness.
Risk factors for molar pregnancy
The cause of molar pregnancy is unknown, but risk factors include:
- maternal age of less than 20 or more than 40 years
- race – 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
After fertilisation, developing cells split into two broad groups – one group becomes the fetus 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 complete molar pregnancies, the fetus doesn’t grow, but the placenta grows abnormally. The villi swell and look like little blisters. These blisters are called a hydatidiform mole.
In partial molar pregnancies there is some development of the fetus but it is not normal and cannot survive. This is called a partial mole.
When a woman has a molar pregnancy she 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
Molar pregnancy is usually diagnosed early with minimal symptoms, but if diagnosis is delayed the following complications can arise:
- 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
- excess thyroid hormone production, which causes heart palpitations and other thyroid hormone effects.
If a molar pregnancy is not treated or does not miscarry completely it can progress and cause a range of serious conditions (known as gestational trophoblastic neoplasia), including:
- persistent GTD – persistent growth of the abnormal 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
Molar pregnancy is diagnosed using:
- 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.
Molar pregnancy 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 molar pregnancy until symptoms become apparent.
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:
- dilatation and curettage – 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 persistent GTD is diagnosed, chemotherapy will be needed.
Further treatment is required in 10 per cent of all cases.
Molar pregnancy can recur
Molar pregnancy can recur (occur again), so regular check-ups are needed. The primary test is the blood test for HCG or a 24-hour collection of urine to measure HCG levels. If the HCG levels are high, then molar pregnancy may have recurred.
It is important to strictly avoid pregnancy for at least a year or so following treatment, because a normal pregnancy will produce HCG and make the blood test ineffective.
In Victoria, all women with a hydatidiform mole pregnancy are registered on the Royal Women’s Hospital’s Gestational Trophoblastic Disease Registry. Follow up is monitored and support is available for women with this diagnosis.
Queensland also has a state registry but in other states in Australia, care is usually provided by a specialist gynaecologist.
Where to get help
This page has been produced in consultation with and approved by:
Royal Women's Hospital
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