Molar pregnancy
A molar pregnancy is rare, complex, and often unfamiliar, which can make it especially distressing to experience.
A molar pregnancy – also called a hydatidiform mole – happens when an abnormal fertilised egg implants in the womb. Instead of developing into a baby and placenta, the cells that would normally form the placenta grow abnormally. Molar pregnancies affect around one in 600 pregnancies.
Many people have never heard of molar pregnancy until they are diagnosed with one. Learning that something so unexpected — and medically complex — has happened can feel overwhelming, particularly when it follows a miscarriage or leads to prolonged follow-up care.
What a molar pregnancy means
A hydatidiform mole may be either partial or complete, depending on the genetic make-up of the fertilised egg. With normal conception each of our cells contains 23 pairs of chromosomes, so a single sperm with 23 chromosomes fertilises an egg with 23 chromosomes, making 46 in all.
In this situation, two sperm fertilise the egg instead of one, creating 69 instead of 46 chromosomes. This is called a triploidy. There is too much genetic material and the pregnancy develops abnormally, with the placenta outgrowing the baby. There may be evidence of a fetus but it will be abnormal and cannot survive.
There have been some (very few) reports of live babies born after what was thought to be a partial mole, but this may have been the result of an extremely rare condition where a normal baby has a mole for a “twin”.
A complete mole is when one (or even two) sperm fertilises an egg cell which has no genetic material inside. Even if the father’s chromosomes double up to make 46 in all, the balance of chromosomes from the mother and father is wrong. Usually the fertilised egg dies at that point but in rare cases it goes on to implant in the uterus. When it does, no embryo grows, only the trophoblast (the cells that will become the placenta) and that grows to fill the uterus with the molar tissue.
In a normal pregnancy, the trophoblast invades, or burrows into and through the lining of the uterus. However, in about 14% of complete moles and 1% of partial moles the trophoblast not only grows very quickly, but also burrows more deeply into the uterus than it should.
In these rare cases, the trophoblast cells can become malignant (cancerous) and invade and spread to other parts of the body. This is called invasive mole. If it is not treated, it can develop into choriocarcinoma. This is an extremely rare complication of hydatidiform mole.
Choriocarcinoma more often arises from other types of pregnancy and it affects one in 50,000 pregnancies. The very small risk of developing invasive mole or choriocarcinoma is the reason that molar pregnancies are followed up. It is also the reason that the follow-up centres are located in units dealing with cancer (oncology) or trophoblastic tumours. They can detect trophoblastic disease very early and the cure rate is almost 100%.
Signs and symptoms
Some women will have no noticeable symptoms of molar pregnancy, or may recognise them only after they have been diagnosed. This is because most of the symptoms are due to very high levels of the pregnancy hormone hCG (human chorionic gonadotrophin), so they can be very like the usual symptoms of pregnancy or miscarriage.
If you have never been pregnant, or have not had particularly strong pregnancy symptoms before, it can be hard to know what is normal and what isn’t.
Signs and symptoms are mainly:
- Missed period/s and a strong positive pregnancy test
- A lot of nausea (feeling sick) or vomiting.
- Irregular bleeding from the vagina. The blood may contain little fluid-filled cysts (like tiny grapes)
- Symptoms like those of a miscarriage, including pain and bleeding
Your doctor may notice other changes that suggest molar pregnancy:
- Your uterus may be larger than expected from your dates
- Your ovaries may be enlarged (due to the high levels of hCG)
- You might have high blood pressure and protein in your urine, though this is rare.
Diagnosing molar pregnancy
After a miscarriage
Most cases of molar pregnancy are diagnosed after what appears to be a “normal” miscarriage where the woman has had surgical management of her miscarriage. You might hear this procedure referred to as an ERPC, an “evac” or a D & C.
In most hospitals, a sample of the tissue that is removed is sent to the laboratory and tested to see if it is normal pregnancy tissue. (This process is called histology and you may be asked to give your permission). This examination can identify molar tissue and thus a molar pregnancy.
There may be a delay between when you have the surgery and when you are told that you have (or might have) a molar pregnancy. It may be some days or a few weeks after your miscarriage when you are contacted by letter or phone call. You may be asked to return to see the doctor before you are told any more.
“I thought nothing could be more devastating than losing a baby, until a month later when they told me it was a partial molar pregnancy. It was painful to realise that for all these weeks there wasn’t a baby growing inside me. It felt like we had been tricked.”
In pregnancy
In some cases, the GP or hospital doctor might suspect a molar pregnancy. If so, they might refer you for one or more of the following:
- A blood test, to measure your hCG levels (this might be done more than once over a few days)
- An ultrasound scan (unless you have just had one)
- An appointment with a hospital gynaecologist or Early Pregnancy Unit
If your doctor diagnoses or strongly suspects a molar pregnancy they will recommend that you have surgery to remove any pregnancy tissue. The diagnosis will then be confirmed by laboratory examination. This process is not a termination of pregnancy (an abortion). In most cases there never was an embryo or it died at a very early stage, and even in a partial mole it will not develop. Even so, you may still feel a sense of loss for what would have been your baby.
Treatment and Follow-Up
The main treatment is surgery to remove the pregnancy tissue. In most cases, this has already been done by the time the diagnosis is confirmed.
Some women may require further surgery if tissue remains, but this is uncommon. About one in ten may need additional medication, including chemotherapy, particularly in rare cases of invasive mole. These treatments are highly effective.
After a molar pregnancy, all women are monitored to ensure hCG levels return to normal. Follow-up usually involves regular blood or urine tests, which are sent to specialist centres.
- Complete mole: Follow-up continues until hCG levels are normal, with a final check four weeks later. If levels take longer than eight weeks to normalise, monitoring continues for six months.
- Partial mole: Follow-up continues until four weeks after hCG levels return to normal. If levels do not fall or rise again, further treatment may be recommended.
- Invasive mole or choriocarcinoma: Rare, but treatment plans and follow-up are clearly explained by the care team.
During follow-up, you will be advised not to get pregnant. If chemotherapy was required, waiting a year before trying again is recommended.
Who does the follow-up?
Depending on where you live, your follow-up will be done at one of the three specialist centres in the UK:
- Charing Cross Hospital in London
- Sheffield
- Ninewells Hospital in Dundee
You are unlikely to have to go there yourself, as they will arrange for your local hospital or clinic to take blood samples and to send these on.
They will send your test results to your GP and your hospital doctor, but you can also contact them directly and they will tell you the result. The procedure may vary a little between the three centres, but not a great deal.
As most women are followed up by Charing Cross Hospital in London, we describe their procedure here:
- You will receive a letter from the follow-up centre telling you that you have been registered for the follow-up programme.
- A few days later you will receive a small box or packet containing a letter for your local hospital or clinic and a small tube or tubes for your blood and urine samples.
- On the date requested, you collect a sample of your first urine of the day and place this in the small tube marked ‘urine’. You then take this urine sample with you to the bloodtest appointment. They will put the blood into their own plain or yellow top tube (the other tube marked ‘serum’ is for lab use only).
- They will put urine and blood samples in the box that you received, and send it to their local lab. From there it goes with the serum to your local centre for processing. You will only need to post yourself if you are doing a urine only sample.
- Once your blood tests are normal, you will only need to send a urine sample, so you can send them from home, without having to go to the hospital or clinic.
“I was monitored for six months and thankfully my levels went down quickly. I also attended one of the support group sessions at Charing Cross Hospital, which was very helpful.”
Support
The experience of a molar pregnancy can be very distressing. We have a monthly Zoom support group for people affected. Contact [email protected] for the next date and meeting link.