12332 Partial Molar Pregnancy

Overview

A partial molar pregnancy is an abnormal pregnancy where the placenta grows into a mass of cysts and the fetus (baby) does not develop normally. It is also called a partial hydatidiform mole. The pregnancy cannot develop into a healthy baby and usually ends as a miscarriage or requires treatment to remove the abnormal tissue.

It is rare. In countries like the UK, about 1 in 700 to 1,000 pregnancies is affected by a molar pregnancy, and most of those are partial molar pregnancies.

It can affect anyone who becomes pregnant, but it is more common in people under 20 or over 40. Having had a molar pregnancy before also increases the risk.

Symptoms

Common symptoms

• Vaginal bleeding in early pregnancy (often dark brown or bright red)
• Severe nausea and vomiting that may be worse than usual morning sickness
• Pelvic pressure, discomfort, or pain
• Sometimes passing small grape-like cysts (this is not always noticed)
• The womb may feel larger than expected for the stage of pregnancy

Causes

Main causes

• A partial molar pregnancy happens when an egg is fertilised by one sperm, but the egg's genetic material is lost and the sperm's chromosomes duplicate. This leads to three sets of chromosomes (triploidy).
• Because of the abnormal genetic makeup, the placental tissue grows into a mass of cysts and the fetus either does not form properly or stops developing very early.

Risk factors

• Maternal age under 20 or over 40
• A previous molar pregnancy (recurrence risk is about 1 in 100)
• A diet low in carotene (a form of vitamin A) – this has been noted in some parts of the world, but it is not a major factor in Western countries

When to see a doctor

See a doctor urgently if:

• If you have heavy bleeding, severe pain, or signs of shock, call your local emergency number immediately.
• If you are pregnant and have any vaginal bleeding, contact your maternity unit or GP for urgent advice the same day.

Book a routine appointment if:

• If you have persistent nausea, vomiting, or any unusual discharge during pregnancy, book an assessment with your doctor or midwife.
• If you have had a molar pregnancy before, talk to your doctor about early monitoring in future pregnancies.

Diagnosis

A partial molar pregnancy is usually found during an ultrasound scan in early pregnancy. The scan may show a mass of abnormal placental tissue and no normal fetal heartbeat. If it is discovered after a miscarriage, the diagnosis is confirmed by examining the tissue under a microscope after it has been removed.

Tests that may be done

• Ultrasound scan (transvaginal or abdominal)
• Blood test to measure the human chorionic gonadotropin (hCG) – the pregnancy hormone
• Pathology examination of the tissue from the womb after a procedure or miscarriage

What to expect at your appointment

If a partial molar pregnancy is suspected, you will be referred to a specialist centre that has expertise in gestational trophoblastic disease. You will have blood tests to check your hCG level. The usual next step is a minor operation called suction curettage to remove the abnormal tissue from the womb. After this, you will need regular blood tests for several weeks or months to make sure the hCG level returns to zero.

Treatment

The abnormal tissue must be removed from the womb. This is usually done with a minor surgical procedure called suction curettage. After removal, you will be followed with hCG blood tests to make sure no abnormal cells remain. In rare cases, if the disease persists or spreads, additional treatment such as chemotherapy may be needed. The treatment plan is always tailored to your individual situation by a specialist team.

Self-care at home

• Rest and allow your body to recover after the procedure.
• Use sanitary pads rather than tampons until your doctor confirms it is safe.
• Avoid sexual intercourse and inserting anything into the vagina (such as tampons) until the bleeding has completely stopped and your doctor says it is okay.
• Take pain relief as recommended by your doctor or pharmacist – do not exceed the advised dose.

Medical treatments

The main treatment is surgical removal of the abnormal tissue. After surgery, close monitoring with hCG blood tests is essential. If the hCG level stays high, rises, or shows signs of spread, your specialist may recommend chemotherapy. Chemotherapy uses medicines to destroy any remaining abnormal cells. The specific medicines and duration depend on the individual case and are managed by a gestational trophoblastic disease centre.

When is surgery considered?

Surgery is the standard first-line treatment for a partial molar pregnancy. The procedure is called suction curettage, and it is usually performed under general anaesthetic. It removes the abnormal tissue from the womb, which is required to stop bleeding and prevent complications.

Living with this condition

After treatment, you will need to attend regular blood tests to check hCG levels. Once your levels are normal for a few consecutive weeks, you will be discharged from follow-up. It is often recommended to wait a certain period (usually at least 6 months) before trying to conceive again, depending on your results. Your specialist will give you clear, personal advice.

Lifestyle tips

• Use reliable contraception to prevent pregnancy during the follow-up period if your doctor advises you to wait.
• Attend every blood test and follow-up appointment – these are vital to ensure any persistent disease is caught early.
• Seek emotional support if you need it – this is a significant loss and it is normal to feel grief.

Diet and exercise

Eat a healthy, balanced diet to help your body recover. You can resume gentle exercise when you feel ready, but avoid heavy lifting and strenuous workouts for a few weeks after surgery. Always follow the advice of your healthcare team.

Mental health and emotional wellbeing

A molar pregnancy can be emotionally difficult. It is a pregnancy loss and may bring feelings of sadness, shock, guilt, or anxiety. These feelings are completely normal. Talk to your GP or a counsellor if the emotions feel overwhelming. You are not alone, and support is available.

Prevention

There is no known way to prevent a partial molar pregnancy. It is caused by a random genetic error at conception, and it is not linked to anything you did or did not do. After one molar pregnancy, the risk of another is slightly higher, but most women with a previous molar pregnancy go on to have a normal pregnancy.

Vaccines

No vaccine is relevant to this condition.

Screening programmes

There is no routine screening for partial molar pregnancy. However, if you have had one before, your doctor may recommend an early ultrasound scan in any future pregnancy to check for recurrence.

Complications

If left untreated

• The abnormal tissue may continue to grow and cause heavy bleeding or infection.
• It can develop into persistent gestational trophoblastic disease, which means abnormal cells remain in the womb and may spread to other parts of the body (known as invasive mole or choriocarcinoma).
• In rare cases, untreated disease can be life-threatening.

Long-term outlook

The outlook is excellent with prompt treatment. More than 90% of women with a partial molar pregnancy are cured by surgical removal alone. During follow-up, if any abnormal cells remain but have not spread, they can often be treated successfully. The cure rate is nearly 100% with appropriate care. After a recommended waiting period, most women are able to have healthy pregnancies in the future.

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