Molar Pregnancy

What is a molar pregnancy?

A molar pregnancy is an abnormal pregnancy which will not result in a live birth. A fertilized egg implants in the uterus, but it does not develop into a healthy embryo. Instead, atypical clusters of trophoblastic cells (which in a normal pregnancy would eventually become the placenta) form fluid filled cysts which are sometimes visualized on ultrasound. This condition is also known as hydatidiform mole, originating from an ancient Greek word hydatid, meaning fluid filled sac, and mole meaning a growth of tissue; it is sometimes referred to by clinicians as trophoblastic disease.

How common is molar pregnancy?

Most people have never heard of molar pregnancy, let alone experienced it. Statistics show that only 1 in around 600 pregnancies are molar with higher rates in Asian populations and the cause is usually described as a problem during fertilization resulting in incorrect genetics. There are two different types of molar pregnancy; complete molar and partial molar.  Whilst diagnosis may be suspected during ultrasound, it cannot be confirmed until trophoblastic tissue is examined in a laboratory.

What is a complete molar pregnancy?

A complete molar pregnancy occurs as a result of having two sets of paternal genes in the fertilized egg, and no maternal genes. (In a normal fertilized egg you would have one set of genes from each parent). This happens because of the release of an egg that is missing genetic information, for example the egg may have lacked a nucleus completely, or the nucleus may have been empty of chromosomes. No embryo develops, only a rapidly growing cluster of trophoblastic cells.

What is a partial molar pregnancy?

A partial molar pregnancy occurs when the fertilized egg contains two sets of paternal genes and one set of maternal genes, instead of one of each. This can happen if the egg is fertilized by two sperm at once, or by one sperm which then reduplicates its genetic information. Sometimes the beginnings of an embryo may be seen on ultrasound, however unfortunately it will not be normal and will never continue to be a live birth.

What are the symptoms of a molar pregnancy?

Due to the rapidly developing cells within a molar pregnancy, women often experience symptoms of early pregnancy as they would with a normal developing embryo.  Nausea and vomiting can be particularly bad due to high levels of the pregnancy hormone HCG (human chorionic gonadotrophin) and women who are admitted to hospital with hyperemesis (severe morning sickness) are often scanned to rule out the possibility of a molar.  Spotting also often occurs in molar pregnancy, and some patients experience some abdominal pain, however it is important to remember that these symptoms are also common in normal developing pregnancies.

How is a molar pregnancy treated?

If your sonographer suspects a molar pregnancy during your scan, you will be informed. Once they have confirmed that the pregnancy is not viable and there is no heartbeat, you may be advised to proceed with some surgery where the pregnancy is gently removed via the vagina. This is normally a day procedure and women usually make a quick recovery (see surgical management of miscarriage for more details about this).

Why do you have to have surgery for molar pregnancy?

Surgery is usually recommended so that clinicians can insure that all of the molar tissue is removed and can be sent to the lab to confirm the diagnosis. Women are then registered with a service which will monitor their HCG levels in subsequent weeks to check that it continues to drop. The levels of HCG (pregnancy hormone) in the blood relates to how many cells are left in the uterus, and this needs to go back down to negative to minimize any further risk.

What are the risks of molar pregnancy?

In the majority of women, HCG levels continue to fall satisfactorily following their surgery and they make a quick recovery. However if the HCG level remains static or begins to rise again, you may require intervention. Occasionally women require a second surgical procedure. A very small percentage of patients require chemotherapy if there is an indication that problematic cells are continuing to develop in their uterus, however this is very rare and the overall cure rate for women with this type of trophoblastic disease is 100% as quoted by Charing Cross Hospital.

Why do molar pregnancies get referred to other hospitals?

Once your local hospital has reached a conclusive diagnosis, molar pregnancy patients, whether complete or partial molar, will be referred to a specialist hospital for their follow up. As mentioned above, this condition is quite rare, so continued care is referred to a centre with relevant expertise. Within the UK, you are likely to be referred to either Charing Cross Hospital in London, Dundee or Sheffield. However it is unlikely that you will have to actually attend these hospitals as the required blood samples and urine samples can be collected locally to where you live and sent to the Molar Centre. The Specialist hospitals will be monitoring your results and keeping in touch with you regarding any concerns or other follow up. During this time it is important that you do not get pregnant again until you have been given the all clear and discharged from the specialist centre. The reason for this is that a new pregnancy would affect your HCG levels and if these suddenly rise rapidly it would be difficult to tell if there is a problem related to any molar tissue remaining.

How long do you get monitored for after a molar pregnancy?

Complete molar patients are usually monitored for 6 months if their HCG falls satisfactorily to normal (non pregnant) levels after the first 8 weeks. Partial molar patients are usually monitored for less time; Charing Cross Hospital requires two normal HCG readings taken at least 4 weeks apart to discharge patients.

Can you prevent a molar pregnancy?

There is nothing you can do to prevent a molar pregnancy, however it is very important not to get pregnant again until you have been given the all clear by your Specialist hospital. Women who have had a previous molar pregnancy have a slightly higher risk of molar in subsequent pregnancies, however the chance of a second molar is still only 1 in 100.