Hydatidiform mole

A hydatidiform mole, also called a molar pregnancy, is an abnormal pregnancy. Placental cells grow in an unusual way, but a healthy pregnancy cannot develop.

The placenta normally supports a growing baby. In a molar pregnancy, the cells that would form the placenta become swollen and grow too quickly. This tissue may look like clusters of small fluid-filled sacs.

There are two main types:

• Complete mole: abnormal placental tissue grows, but there is no developing fetus
• Partial mole: abnormal placental tissue grows alongside some fetal or embryonic tissue, which cannot develop into a healthy baby

A hydatidiform mole is part of a group of conditions called gestational trophoblastic disease, or GTD. “Gestational” means related to pregnancy, and “trophoblastic” refers to cells that normally help form the placenta.

Most moles are successfully treated by removing the abnormal tissue. Follow-up blood or urine tests are important because small amounts of tissue can sometimes remain and continue growing. This is called persistent GTD or gestational trophoblastic neoplasia, often shortened to GTN. It is highly treatable in most cases.

A molar pregnancy also means the loss of a pregnancy. You may feel grief, shock, anger, or confusion while also dealing with treatment and follow-up. These responses are understandable.

Some hydatidiform moles cause no clear symptoms and are first found during a routine pregnancy ultrasound.

When symptoms occur, they can include:

• Vaginal bleeding during early pregnancy
• Nausea and vomiting that are more severe than expected
• A uterus that is larger than expected for the stage of pregnancy
• Pelvic discomfort or pressure
• Passing small, fluid-filled sacs from the vagina
• Pregnancy symptoms that feel unusually strong

A molar pregnancy can produce high levels of human chorionic gonadotropin, or hCG. This is the pregnancy hormone detected by pregnancy tests. High hCG may contribute to severe nausea and can sometimes affect the thyroid gland.

Possible thyroid-related symptoms include a racing heartbeat, shaking, feeling unusually hot, or losing weight despite being pregnant. These symptoms have several possible causes and do not confirm a molar pregnancy.

Rarely, high blood pressure and signs of pre-eclampsia develop unusually early in pregnancy. Pre-eclampsia normally occurs later and can cause headache, visual changes, swelling, or pain below the ribs.

Symptoms alone cannot diagnose a hydatidiform mole. Vaginal bleeding and nausea are common in pregnancy and may have other explanations.

A hydatidiform mole begins with a random error involving chromosomes at fertilisation. Chromosomes carry genetic information.

In a complete mole, an egg without working maternal chromosomes is fertilised. The resulting genetic material usually comes only from the sperm, so a fetus cannot form.

In a partial mole, the fertilised egg usually receives an extra set of chromosomes. Some fetal tissue may begin to form, but it cannot develop into a viable pregnancy.

These errors usually happen by chance. A molar pregnancy is not caused by exercise, sex, stress, food, work, or something you did during pregnancy. It is not usually an inherited condition.

The chance is higher if you have had a previous molar pregnancy. Age also affects risk, with moles occurring more often at the youngest and oldest ends of reproductive age. However, most people who develop one have no known risk factor.

An ultrasound may first raise concern about a molar pregnancy. A complete mole may show abnormal tissue filling the uterus without a fetus. A partial mole can be harder to recognise because it may initially resemble a miscarriage or a pregnancy with serious developmental problems.

Your care team will usually measure hCG in your blood. The level may be higher than expected, but hCG alone cannot confirm the diagnosis because levels differ widely in normal and abnormal pregnancies.

The diagnosis is usually confirmed by examining tissue under a microscope after it has been removed from the uterus. This is called a pathology examination. Special laboratory tests may help distinguish a complete mole, partial mole, and non-molar miscarriage.

Other assessments may include:

• A blood count to check for anaemia from bleeding
• Blood group testing
• Kidney, liver, or thyroid tests when clinically needed
• Further imaging if hCG does not fall as expected

After treatment, hCG is checked regularly until it returns to normal and remains there for the period advised by the specialist service. The follow-up schedule is different for complete and partial moles and may also differ between healthcare systems.

The usual treatment is to remove the molar tissue from the uterus. This is commonly done through the vagina and cervix using gentle suction, usually while you are under anaesthesia. It is often called suction evacuation or suction curettage.

The removed tissue is sent to a laboratory to confirm the diagnosis. Medication for pain and bleeding may be given around the procedure. If your blood group is Rh-negative, your team will decide whether you need anti-D immunoglobulin according to local practice.

A hysterectomy, which removes the uterus, may occasionally be considered if you do not want a future pregnancy or if there are other medical reasons. It is not the usual treatment for everyone. Follow-up hCG testing is still required because molar cells can rarely remain elsewhere in the body.

After removal, blood or urine hCG tests monitor whether all active molar tissue has gone. Levels should fall over time. Missing follow-up tests can delay recognition of persistent disease, even if you feel well.

If hCG stays level, rises, or remains detectable longer than expected, you may be diagnosed with persistent GTD or GTN. Treatment usually involves chemotherapy, meaning medicines that destroy abnormal cells. Lower-risk disease is often treated with one medicine, while higher-risk disease may require a combination of medicines. Surgery is sometimes used in selected cases.

Treatment is organised by clinicians experienced in GTD. Most people keep their fertility after treatment, including after chemotherapy, although recovery time and pregnancy planning are individual.

The main early complication is bleeding. Significant blood loss can cause anaemia, which may lead to tiredness, weakness, breathlessness, or dizziness.

Other possible complications include:

• Infection after tissue removal
• Severe nausea, vomiting, and dehydration
• Overactivity of the thyroid caused by high hCG
• Ovarian cysts related to hormone stimulation
• Persistent GTD or GTN

Persistent disease is more common after a complete mole than after a partial mole. It does not mean that you did anything wrong or that the first procedure failed. Microscopic cells can remain even when the uterus appeared empty.

Rarely, abnormal cells become an invasive mole or a cancer called choriocarcinoma. These conditions can spread beyond the uterus, but they are often very sensitive to chemotherapy. Treatment and follow-up may then continue for longer.

Emotional effects can also be significant. You may be coping with pregnancy loss while being told that monitoring or cancer treatment could be needed. Support from a pregnancy-loss service, counsellor, GTD centre, or trusted people may help.

A hydatidiform mole usually cannot be prevented because it results from a chance chromosome error during fertilisation. There is no proven food, supplement, activity, or lifestyle change that prevents it.

After treatment, you will normally be advised not to become pregnant until hCG follow-up is complete and your specialist team says it is safe to try. This does not prevent another mole directly. It allows hCG to be interpreted correctly, because a new pregnancy also raises this hormone and could hide persistent disease.

Your team can help you choose contraception during monitoring. If you later become pregnant, an early ultrasound may be offered to confirm that the pregnancy is developing normally.

Physical recovery after removal is often similar to recovery after a miscarriage. Bleeding or spotting and mild cramping may continue for a time, then gradually settle. Follow the discharge instructions from your treatment centre about activity, sex, menstrual products, and signs of infection.

Your periods may take time to return. Pregnancy tests can remain positive while hCG is falling, so a home test does not show whether follow-up is complete.

Monitoring may last for weeks or months. It may continue longer if hCG falls slowly or if you need treatment for persistent disease. Attend every scheduled test, even when you feel completely well.

Most people do not need further treatment after the mole is removed. If chemotherapy is needed, the outlook is still usually very good, but treatment may affect energy, work, family life, and pregnancy plans for a period of time.

A previous molar pregnancy does not usually stop you from having a healthy pregnancy later. The chance of another mole is higher than for someone who has never had one, but recurrence remains uncommon. Future pregnancies may involve early ultrasound and an hCG check after the pregnancy ends.

Emotional recovery has no set timetable. Waiting for test results can be stressful, and others may not understand why follow-up continues after the pregnancy has ended. Ask your care service what emotional and practical support is available.

Keep all routine hCG appointments and contact your treatment service if you cannot attend. Routine monitoring is essential but is not usually an emergency.

Seek prompt medical advice if you develop:

• Bleeding that is increasing rather than settling
• Fever, chills, or foul-smelling vaginal discharge
• Worsening pelvic or abdominal pain
• Repeated vomiting or difficulty keeping fluids down
• A racing heartbeat, shaking, or feeling unusually hot
• A new positive pregnancy test during follow-up

Seek emergency care for very heavy bleeding, fainting, severe weakness, chest pain, difficulty breathing, coughing up blood, a seizure, or a sudden severe headache with weakness or visual changes.

If you are currently pregnant and pass grape-like sacs or tissue, contact urgent pregnancy care. Keep the tissue only if the service advises you to do so.

Is a hydatidiform mole a baby?

A complete mole does not contain a fetus. A partial mole may contain some fetal or embryonic tissue, but it cannot develop into a healthy baby. Even so, this is still a pregnancy loss, and grief is valid.

Is a molar pregnancy cancer?

A hydatidiform mole is not usually cancer. A small proportion persist after removal and become GTN. Rarely, this includes choriocarcinoma. These conditions require specialist treatment and are often highly responsive to chemotherapy.

Why do I need hCG tests after the tissue is removed?

Tiny amounts of active molar tissue may remain without causing symptoms. hCG testing is a sensitive way to detect this. Falling levels suggest the tissue is disappearing; stable or rising levels may mean further assessment is needed.

When can I try to get pregnant again?

Wait until your specialist service confirms that hCG monitoring is complete and it is safe to try. The timing differs according to the type of mole, how quickly hCG becomes normal, and whether you needed chemotherapy.

Will I be able to have a normal pregnancy later?

Most people can become pregnant and have a healthy pregnancy after completing follow-up. Your next pregnancy may be checked with an early ultrasound, and the placenta may be examined after delivery or another pregnancy ending.

Did I cause the molar pregnancy?

No. It results from a chromosome error at fertilisation and is not caused by stress, exercise, sex, diet, or ordinary daily activities.