5. What is a molar pregnancy?

[taken from nhs.uk]

What is a molar pregnancy?

A molar pregnancy is an unsuccessful pregnancy, where the placenta and foetus do not form properly, and a baby does not develop.

In a normal pregnancy, the placenta provides nourishment to the developing baby and removes waste products. The placenta is made up of millions of cells known as trophoblastic cells.

In a molar pregnancy, these cells behave abnormally as soon as the egg has been fertilised by the sperm. This results in a mass of abnormal cells that can grow as fluid-filled sacs (cysts) with the appearance of white grapes. These cells grow rapidly within the womb, instead of developing into a baby. The abnormal cells are referred to as a “mole”, which is from the Latin for mass or lump.

Molar pregnancy is also called a hydatidiform mole and is a pre-cancerous form of gestational trophoblastic disease.

Molar pregnancies are caused by an imbalance in genetic material (chromosomes) in the pregnancy. This usually occurs when an egg that contains no genetic information is fertilised by a sperm (a complete molar pregnancy), or when a normal egg is fertilised by two sperm (a partial molar pregnancy).

In complete molar pregnancy, the embryo does not develop at all. In a partial molar pregnancy, a foetus can develop but never results in a viable baby, due to the imbalance between the male and female chromosomes.

Symptoms and diagnosis

There are often no signs that a pregnancy is a molar pregnancy. In most cases, the problem is first spotted during an ultrasound scan, which may be the first pregnancy scan at 10-14 weeks.

If there are symptoms, they usually appear between weeks 4 and 12 of pregnancy. The most common symptom is bleeding or losing brown-red fluid from the vagina.

Sickness and vomiting may be more severe than in a normal pregnancy.

Bleeding usually requires an ultrasound scan. If this scan is abnormal, an evacuation of the uterus is performed. This is when the molar pregnancy is removed, usually with a surgical procedure called suction evacuation. The surgery involves opening your cervix (neck of the womb) with a small tube known as a dilator, and removing any remaining tissue with a suction device. Tissue from the pregnancy is then sent to a laboratory to confirm whether it is a molar pregnancy.

If a woman has a miscarriage or a termination for other reasons, tissue may be sent to a laboratory for analysis. This may confirm that the pregnancy was molar, even if a molar pregnancy wasn’t suspected.


A molar pregnancy usually needs to be removed surgically. This is done with a suction evacuation, under the care of a gynaecologist.

In some cases, molar pregnancy can be treated with the removal of the womb (hysterectomy), but this is usually only if you no longer wish to have children.

Almost all cases of molar pregnancy are successfully cured.

After treatment

Following the mole’s removal, some cells will be left in the womb. These cells usually die off over time in around 90% of women.

To check the cells have died, all women who have had a molar pregnancy in the UK undergo monitoring of the hormone hCG (human chorionic gonadotrophin) via the National Trophoblastic Screening Centre’s surveillance programme. hCG is the pregnancy test hormone produced by a normal placenta, but also by the mole cells, and is the hormone detected in a pregnancy test. It can also be detected in blood and urine tests.

Women on the surveillance programme send in blood or urine samples every two weeks. This is so they can be monitored for signs of persistent trophoblastic disease, which is a risk after all molar pregnancies (see below).

Persistent trophoblastic disease needs further treatment with chemotherapy.

Hormone monitoring will identify the small number of women who develop a persistent or invasive mole (see below). In these cases, levels of hCG will stay steady or rise, rather than fall.


In some cases, the molar disease left after the evacuation of the uterus regrows rather than dies out, and is then known as a persistent disease.

This is one of the malignant forms of gestational trophoblastic disease and includes invasive mole and choriocarcinoma. A further suction evacuation may help in a few patients, but chemotherapy is usually necessary to cure the problem.

The risk of needing further treatment is:

  • 1 in 10 after a complete molar pregnancy
  • 1 in 100 after a partial molar pregnancy

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