Gestational trophoblastic disease (GTD) is the name given to a group of uncommon conditions in which the cells that would normally form the placenta grow abnormally. The most common form is a molar pregnancy, sometimes called a hydatidiform mole.
A molar pregnancy cannot develop into a healthy baby. Although the diagnosis can be frightening, it is important to remember that it happens by chance and is not caused by anything either parent did or did not do. With appropriate treatment and follow-up, almost everyone makes a full recovery.
What is a molar pregnancy?
A molar pregnancy begins when an egg and sperm join in an abnormal way at conception. As a result, the pregnancy and placenta do not develop normally.
There are two main types:
- Complete molar pregnancy: Abnormal placental tissue grows inside the womb, but a baby does not develop.
- Partial molar pregnancy: Some early signs of a baby may be present, but the baby has severe genetic abnormalities and cannot develop or survive.
Molar pregnancies are uncommon, affecting approximately 1 in every 600–700 pregnancies in the UK. They may be slightly more common among very young teenagers, women over the age of 45, women of Asian heritage and those who have previously experienced a molar pregnancy. However, most cases occur without any clear risk factor. NHS guidance
What is gestational trophoblastic neoplasia?
After a molar pregnancy has been removed, a small amount of abnormal tissue can occasionally remain and continue to grow. This is known as persistent gestational trophoblastic disease or gestational trophoblastic neoplasia (GTN).
GTN is a rare form of cancer, but it is highly treatable. It includes conditions such as an invasive mole and choriocarcinoma, as well as much rarer placental tumours. GTN can occasionally develop after a miscarriage, termination of pregnancy, ectopic pregnancy or full-term birth—not only after a molar pregnancy.
Approximately 1 in 10 women with a complete molar pregnancy and 1 in 100 with a partial molar pregnancy may require further treatment. These figures vary slightly between specialist centres. The great majority of affected women are successfully treated.
What symptoms can occur?
Some women have no obvious symptoms and the condition is first suspected during a routine pregnancy scan. Others receive the diagnosis after tissue from a miscarriage has been examined in a laboratory.
Possible symptoms include:
- Vaginal bleeding or a dark vaginal discharge during early pregnancy
- Severe or persistent nausea and vomiting
- A womb that appears larger than expected for the stage of pregnancy
- Abdominal discomfort or swelling
- Pregnancy hormone levels that are unusually high
- Symptoms of an overactive thyroid, such as a rapid heartbeat or trembling
- High blood pressure or pre-eclampsia unusually early in pregnancy
These symptoms do not necessarily mean that someone has a molar pregnancy. Bleeding and sickness, for example, can occur for many other reasons. However, any bleeding or significant concern during pregnancy should be discussed with a midwife, GP or early-pregnancy team.
How is it diagnosed?
A molar pregnancy may be suspected following an ultrasound scan. The scan may show that the pregnancy has not developed normally or that the placental tissue has an unusual appearance.
Blood tests are also used to measure human chorionic gonadotrophin, commonly called hCG. This is the hormone detected by pregnancy tests. A molar pregnancy often produces more hCG than a normally developing pregnancy, although a high result alone cannot confirm the diagnosis.
The final diagnosis is usually made by examining pregnancy tissue in a laboratory after a miscarriage or treatment. This examination can establish whether the pregnancy was molar and, if so, whether it was complete or partial.
How is a molar pregnancy treated?
A molar pregnancy cannot continue as a healthy pregnancy, so the abnormal tissue must be removed. Most women are treated with a short operation under general anaesthetic. A small suction tube is passed through the cervix—the opening of the womb—to gently remove the tissue.
Medication may be appropriate in selected circumstances, although surgery is the most common treatment. The most suitable approach will depend on the type of molar pregnancy, the stage of pregnancy, the woman’s symptoms and her individual circumstances.
The removed tissue is sent to a laboratory to confirm the diagnosis. Women with a rhesus-negative blood group may also be offered an anti-D injection.
For most women, removing the molar tissue is the only treatment required. Cancer Research UK
Why is follow-up so important?
After treatment, hCG levels are checked regularly using blood or urine samples. These tests show whether all the abnormal cells have disappeared.
A falling hCG level is reassuring. If the level stops falling, begins to rise or remains detectable for longer than expected, it may mean that some abnormal tissue is still present. Further tests and treatment may then be needed.
In the UK, women diagnosed with a molar pregnancy are registered with one of three specialist centres:
- Charing Cross Hospital in London
- Weston Park Hospital in Sheffield
- Ninewells Hospital in Dundee
The length of follow-up depends on whether the mole was complete or partial and how quickly the hCG level returns to normal. Following a partial mole, monitoring can usually stop after two normal samples taken at least four weeks apart. Monitoring after a complete mole generally continues for at least six months and may last longer if the hCG level falls slowly. Your specialist centre will provide an individual timetable.
It is essential to complete the recommended monitoring, even if you feel well, because persistent abnormal cells do not always cause symptoms.
What happens if further treatment is needed?
If hCG levels remain raised or begin to increase, the specialist team will arrange additional investigations. These may include further blood tests and scans to establish whether abnormal cells remain and whether they have spread.
Treatment usually involves chemotherapy. Women with lower-risk disease often need only one chemotherapy medicine, while those with higher-risk disease may need a combination of medicines.
Although the word “chemotherapy” can be alarming, GTN is particularly sensitive to treatment. Cure rates are extremely high, especially when the condition is identified through routine hCG monitoring. Specialist follow-up programmes report cure rates of approximately 98–100%.
When should medical advice be sought?
Contact your GP, midwife or early-pregnancy service if you are pregnant and experience:
- Vaginal bleeding or a dark discharge
- Severe or persistent vomiting
- A rapidly enlarging abdomen
- Significant abdominal pain
- Any other symptoms that concern you
Medical advice should also be sought for persistent or irregular bleeding following a miscarriage, termination, ectopic pregnancy or birth—particularly if a pregnancy test remains positive.
Urgent assessment is needed for severe bleeding, breathlessness, coughing up blood, fainting, a new seizure, weakness or numbness. These symptoms are uncommon but should never be ignored.
Can I become pregnant again?
A previous molar pregnancy does not usually affect fertility. Most women later have healthy pregnancies, and approximately 99 in every 100 will not experience another molar pregnancy.
It is usually advisable to avoid becoming pregnant until the specialist follow-up programme has been completed. A new pregnancy naturally raises hCG levels, making it difficult to tell whether an increase is due to pregnancy or remaining molar cells.
Most contraceptive methods can be used during follow-up, although an intrauterine device or system—such as a copper or hormonal coil—is generally delayed until hCG has returned to normal. Your healthcare team can help you choose a suitable method.
Once your specialist confirms that follow-up is complete, you can usually begin trying for another pregnancy. An early ultrasound scan may be offered in a future pregnancy for reassurance.
Emotional recovery matters too
A molar pregnancy is a pregnancy loss as well as an unusual medical diagnosis. Feelings of grief, anxiety, confusion, anger or fear about future pregnancies are entirely understandable. The need for repeated tests can also make it difficult to feel that the experience is over.
Partners may be affected differently and may need support as well. Help is available through GPs, early-pregnancy services, specialist GTD centres, counselling services and pregnancy-loss organisations. There is no correct timetable for emotional recovery.
The key message
A molar pregnancy is rare, happens by chance and is not anyone’s fault. Most women need only a short procedure followed by monitoring of their pregnancy hormone levels. A small number require additional treatment, but cure rates are excellent.
Early diagnosis, careful follow-up and support from a specialist team allow the overwhelming majority of women to recover fully and have healthy pregnancies in the future.
This article provides general information and is not a substitute for individual medical advice. Anyone concerned about symptoms during or after pregnancy should contact their GP, Midwife, Obstetrician or Gynaecologist for appropriate advice and follow up.
Ref: RCOG GTG No.38