Molar pregnancy: all you need to know

Leading consultant gynaecologist Mr Narendra Pisal explores molar pregnancy, including the signs and symptoms, risk factors and impact on future pregnancies.

What is a molar pregnancy?

A molar pregnancy is a rare complication in which the placenta and fetus do not develop normally, resulting in a non-viable pregnancy. It affects approximately 1 in every 600 to 1,000 pregnancies and is also referred to as a Hydatidiform mole or Gestational trophoblastic disease (GTD).

There are two types of molar pregnancies: partial and complete. In a partial molar pregnancy, an abnormal placenta develops alongside a non-viable fetus. In contrast, a complete molar pregnancy involves abnormal placental tissue without any fetal development.

Signs and symptoms

Many molar pregnancies are asymptomatic and are often discovered during routine early pregnancy ultrasound scans. These scans may reveal an abnormal placenta, sometimes with a non-viable fetus. Diagnosis can also occur following a miscarriage, when tissue samples are sent for further analysis.

Common symptoms include:

• Morning sickness, often more severe than usual due to elevated pregnancy hormone levels (beta-hCG).
• Abdominal pain caused by a rapidly growing uterus or, in some cases, a pregnancy-related cyst (luteal cyst).
• Vaginal bleeding, which may indicate miscarriage.

Causes and risk factors

A molar pregnancy results from an abnormal fertilization process. In a complete molar pregnancy, an empty egg (with no chromosomes) is fertilised by two sperm, leading to two sets of paternal chromosomes. A partial molar pregnancy happens when a normal egg is fertilized by two sperm, resulting in three sets of chromosomes (triploidy).

Factors that may increase the risk include:

• Maternal age at the extremes (teenagers or women over 45).
• Asian ethnicity.
• A previous molar pregnancy.

Treatment and follow-up

Treatment typically involves a surgical procedure to remove the pregnancy tissue under ultrasound guidance. Molar pregnancies are registered with specialised centers in the UK, including Charing Cross Hospital in London, as well as centers in Sheffield and Dundee.

After treatment, monitoring beta-hCG levels for six months is essential to ensure that the condition does not progress to persistent trophoblastic disease, also known as Gestational trophoblastic neoplasia (GTN). This is usually managed by the specialist centres, which may request that women send urine samples by mail. In some cases, a second ultrasound and repeat surgical procedure may be necessary if there is residual pregnancy tissue. In rare instances, this tissue can become malignant and may require chemotherapy.

Impact on sexual activity, contraception, and future pregnancies

Following a molar pregnancy, it is recommended to avoid conception for at least six months. Barrier contraception, such as condoms, is preferred as hormonal contraception and intrauterine devices (IUDs) may not be suitable. In future pregnancies, early ultrasound scans and beta-hCG monitoring are recommended due to a slightly increased risk of recurrence (about 1 in 100). Beta-hCG monitoring continues for six months after any subsequent delivery and is coordinated by specialist centres.

Connection to cancerous cells

In a small number of cases, molar pregnancies can develop into cancer, specifically Choriocarcinoma, a type of cancer that originates in the placenta. However, this cancer is highly responsive to chemotherapy, with a very favourable prognosis. This is why monitoring beta-hCG levels for six months following a molar pregnancy is crucial.

If you would like to book a consultation with Mr Pisal, do not hesitate to do so by visiting his Top Doctors profile today.