Molar Pregnancy: Symptoms, Diagnosis, and Treatments

Molar pregnancy is very rare. It is also called “a mole".  A molar pregnancy is the result of a (purely chance) genetic error during the fertilization process that in turn causes the growth of abnormal tissue (which is not an embryo) within the uterus.

The growth of this material is very rapid compared to normal foetal growth. It has the appearance of a large and random collection of grape-like cell clusters. There are two types of hydatidiform molar pregnancy, ‘complete’ and ‘partial’.

​In a ‘complete mole’ the mass of tissue is completely made up of abnormal cells that would have become the placenta in a normal pregnancy. There is no foetus and nothing can be found at the time of the first scan.

​In a ‘partial mole’, the mass may contain both these abnormal cells and often a foetus that has severe defects. In this case the foetus will be consumed by the growing abnormal mass very quickly.

Another (extremely rare) version of a partial mole is when twins are conceived but one embryo begins to develop normally whilst the other is a mole. In these cases, the healthy embryo will again very quickly be consumed by the abnormal growth.

Symtoms & Diagnosis 

The most common symptom of a mole is vaginal bleeding during the first trimester, however very often no outward signs of a problem appear and the mole can only be diagnosed by use of ultrasound scanning.

Occasionally, a uterus that is too large for the stage of the pregnancy can be an indication. NOTE: Vaginal bleeding does not always indicate a problem.

​If a mole is suspected, a blood test is normally ordered to measure the level of the hormone b-HCG “Beta Human Chorionic Gonadotropin”.  A ‘complete’ molar pregnancy produces this hormone in the same way as a normal foetus, but in very high amounts.

A ‘partial’ mole may not produce noticeably high levels and can only be found by ultrasound. An ultrasound is the normal way to diagnose a molar pregnancy. If a mole is found, a series of tests will be done to check for other medical problems such as pre-eclampsia or an overactive thyroid gland.

Treatment Options

A molar pregnancy must be removed as completely as possible by use of the “Dilation & Evacuation” procedure. This is normally performed under general anaesthetic for molar pregnancies (due to the large amount of tissue that needs to be removed).

In the case of women that wish to have no more children, then a hysterectomy is an option (this is a very difficult decision and should not be taken lightly).

Gestational Trophoblastic Disease (GTD)

About 90% of women that have a “mole” removed require no further treatment; however very careful follow-up procedures are needed with weekly then fortnightly blood tests required for about 6 months to 1 year after the mole is removed. These tests specifically record the levels of b-HCG hormone in the system.

If microscopic traces of the mole remain in the uterus (which is normal), then they can occasionally begin to grow again as before and also pose a cancerous-type threat to the lungs, liver, kidneys, spine and intestines of the mother. Any further growth of the mole will result in rising levels of b-HCG and can alert your doctor to a problem. This growth is called Gestational Trophoblastic Disease or 'GTD' for short.

After the Operation

The normal pattern is that after the operation, the b-HCG levels will fall off steadily over the course of about 3 to 4 weeks, and then more slowly until your next natural menstrual cycle occurs when they should fall again to fairly low levels. The doctor will be looking for a reading of zero (below 3 is often presumed to be zero) for at least three months in a row before he/she should be satisfied that the mole is completely eradicated and that a new pregnancy can be attempted.

After the operation, you may be required to take a full abdominal and chest x-ray to ensure that there is no infestation (metastasis) to the spine, lungs or other vital organs. Very rarely chemotherapy may be needed to remove the remains of the molar pregnancy if it persists as a carcinoma. In very extreme cases an hysterectomy may be needed.

After a molar pregnancy, your doctor will normally advise you to wait 6 months to 1 year before trying to become pregnant again. It is safe to use birth control pills during this time.

The chances of having a second molar pregnancy are only about 1%.

Kate Trout

Hi there, I'm Kate! I started Maternity Glow to be a place to learn all about practical parenting tips, baby care tricks, and healthy-living hacks for new and expecting moms.

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