What is a molar pregnancy?
A molar pregnancy is an uncommon type of pregnancy loss where an egg is fertilised but a baby does not develop. If you have a molar pregnancy, it wasn’t caused by anything you did or didn’t do.
A pregnancy starts with a sperm fertilising an egg. The fertilised egg travels to the womb (uterus) where it implants. A molar pregnancy occurs when the cells that normally form a placenta grow into a clump of abnormal cells instead.
A molar pregnancy is also called a hydatidiform mole. It can be complete or partial.
In a complete molar pregnancy, an embryo does not develop at all. It usually occurs when an egg that does not contain any genetic material is fertilised by a sperm.
In a partial molar pregnancy, a fetus can develop, but it will be abnormal and cannot survive. A partial molar pregnancy usually develops when a normal egg is fertilised by 2 sperm.
What are the symptoms of a molar pregnancy?
Women with a molar pregnancy often feel pregnant. You may have pregnancy symptoms such as sore breasts or morning sickness.
This is because the pregnancy hormone called human chorionic gonadotropin, or (hCG) is still made when you have a molar pregnancy. Indeed, the abnormal placenta often makes higher-than-normal amounts of hCG. This can cause severe morning sickness.
Other signs and symptoms may include:
- vaginal bleeding or a dark discharge
- the uterus feeling larger than it should be for the stage of pregnancy
Some women have other problems, including:
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What causes a molar pregnancy?
Nobody knows why a molar pregnancy happens.
They occur more often in:
- women younger than 15 years
- women above the age of 45 years
- women who have had a molar pregnancy before
How is a molar pregnancy diagnosed?
If you have symptoms that you are concerned about, see your doctor or midwife. They will ask about your symptoms and examine you.
Your doctor may recommend an ultrasound scan and a blood test to check your pregnancy hormone level.
Some women may discover they have a molar pregnancy at their first routine pregnancy ultrasound scan. Others may find out about a molar pregnancy after a miscarriage or termination, if the pregnancy tissue is examined under a microscope.
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How is a molar pregnancy treated?
A molar pregnancy needs to be removed to avoid complications. This is done in a hospital or clinic by a specialist doctor. You can usually go home on the same day as the procedure.
The specialist doctor will remove the tissue from your womb vaginally. The cells from the molar pregnancy are tested in a laboratory. Having the tissue removed is enough treatment in most cases of molar pregnancy.
In some cases, some of the molar tissue persists. It can grow deeper into the womb and spread. This is called an ‘invasive mole’ and needs further treatment.
Rarely, the molar tissue turns into a cancer called ‘choriocarcinoma’, which needs further treatment.
To check that the molar tissue is completely gone, your doctor will ask you to have weekly blood tests. These are to check your hCG level until it returns to normal. Once it returns to normal, you might be asked to have monthly blood tests for another 6 months to make sure all is well.
A molar pregnancy does not affect your chances of getting pregnant again. But you will probably be recommended to wait for your doctor’s all-clear to fall pregnant again.
Talk to your specialist about the best type of contraception to use while you are avoiding pregnancy.
The loss of a pregnancy can be devastating, regardless of how it happens. The long follow-up involved in molar pregnancy can also make it difficult to move forward.
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Last reviewed: July 2022