What is a molar pregnancy?


by Mother & Baby |

We spoke to obstetrician and gynaecologist Dr Ellie Rayner to find out more about a molar pregnancy including what it is and what to do if you are concerned.

What is a molar pregnancy?

 A molar pregnancy is a very rare complication of pregnancy and occurs when an abnormally fertilised egg implants in the womb. In a healthy pregnancy, one single sperm with 23 chromosomes fertilises one single egg, also with 23 chromosomes, making 46 chromosomes in total.

In a molar pregnancy, there is an imbalance in the number of chromosomes from either the egg or sperm causing abnormal development from the beginning.

What are the types of molar pregnancy? 

There are two types of molar pregnancy, partial or complete depending on the genetic make-up of the fertilised egg. 

A partial mole occurs when two sperm fertilise the same egg, creating 69 chromosomes instead of 46 resulting in too much genetic material. 

A complete mole occurs when one or two sperm fertilise an ‘empty' egg, an egg with no genetic material inside. The sperms genetic material double to give 46 chromosomes, however as all of the genetics have come from the father, the balance is still abnormal and cannot develop into a baby.

Can a molar pregnancy survive?

Unfortunately, a molar pregnancy will not survive and will not grow into a healthy baby.

What causes a molar pregnancy?

We don’t know exactly what causes a molar pregnancy and it is important to know that there is nothing that you or your partner did or didn’t do. Overall molar pregnancy is uncommon; for every 714 live births, there will be one pregnancy affected in this way.

There are some factors that can increase the chance of a molar pregnancy such as becoming pregnant as a teenager or over the age of 45 years, being of Asian origin or if you have had a previous molar pregnancy.

What are the signs and symptoms of molar pregnancy?

Some women may not experience any symptoms at all but it is common for women to report irregular or sometimes heavy vaginal bleeding in early pregnancy. Some women report severe morning sickness, due to the higher than normal levels of pregnancy hormone (human chorionic gonadotrophin (hCG)).

It can be difficult to diagnose so you may be offered additional blood tests and scans and follow-up with your local early pregnancy unit. Sometimes a molar pregnancy is only found after you have had other treatment for a miscarriage when the pregnancy tissue is examined under the microscope and your local hospital will contact you directly if this is the case.

What is the treatment for a molar pregnancy?

The best treatment for a molar pregnancy is surgery to remove the abnormal tissue from your womb (uterus) and follow up blood tests to ensure your pregnancy hormone levels return to normal. Rarely, a molar pregnancy can develop into a more serious condition called Gestational Trophoblastic Neoplasia, a rare form of cancer where the molar pregnancy cells keep growing.

After the operation, if you are confirmed to have a molar pregnancy, you will be asked if your details can be registered with one of three specialist centres in either London, Sheffield or Dundee to monitor your recovery and make sure there are no ongoing complications or further treatment required.

What should I do if I think I have a molar pregnancy?

If you have any symptoms you are worried about during early pregnancy, including any bleeding it is important to speak to your GP as soon as possible. If it is outside normal daytime practice opening hours you can speak to the out of hours team or if you are especially concerned, such as experiencing very heavy vaginal bleeding, your local Accident and Emergency department are open 24 hours a day. If you would like any more information, the Royal College of Obstetricians and Gynaecologists have a patient information section on their website with detailed information on molar pregnancy and Gestational Trophoblastic Neoplasia.

Meet the expert: Dr Ellie Rayner is an obstetrician and gynaecologist. She is the founder of The Maternity Collective. Follow them on social media @thematernitycollective.

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