Find out more about molar pregnancy and how we manage it at Charing Cross Hospital.


About molar pregnancy

A molar pregnancy occurs as a result of an abnormality when the sperm fertilises the egg. Despite the fertilised egg (or ovum) growing, dividing, and producing a positive pregnancy test result, there is no viable foetus and the pregnancy can never result in a baby.

Molar pregnancies are divided into two different types, complete and partial, which differ in their genetic make-up, their development and in the chance of needing additional treatment. Molar pregnancies are fairly rare, happening in roughly one case for every 600 pregnancies in the UK.

Complete molar pregnancy

In a complete molar pregnancy, the mother's genetic material in the egg is lost at the time of fertilisation. When fertilisation occurs it is with either one or two sperm, and a fertilised egg is formed from the male genetic material only. In a complete molar pregnancy the embryo does not develop at all but the placental tissue grows quickly. It is very abnormal and forms lots of cysts.

If untreated, a complete molar pregnancy would normally miscarry by 16 to 18 weeks of gestational age. However, the diagnosis is usually made earlier as a result of abnormal bleeding or with the initial booking ultrasound.

Partial molar pregnancy

A partial mole is also genetically abnormal. In the partial molar pregnancy there are three sets of chromosomes instead of the usual two and this is called triploidy. The mother's genetic material from the ovum is retained, but it is fertilised by two sperm instead of one.

As the partial mole has male and female chromosomes, a foetus can briefly develop, but due to the imbalance between the male and female chromosomes the development is highly abnormal and the foetus can never develop into a baby.

Causes of molar pregnancies

Although some studies have linked molar pregnancy with dietary or genetic factors, the real cause of molar pregnancy is still unknown. Molar pregnancies appear to be more common at the beginning and end of the reproductive age group. Compared to women aged between 20 and 40 the risk for girls under 15 who become pregnant is approximately 1.5 times higher and for women aged over 45 the risk is 20 to 50 times higher. The other group who are at higher risk of having a molar pregnancy are women who have had one before. Here the risk is about five times higher than normal, which works out as about a one in 100 chance of having a second molar pregnancy.

The figures for the UK in 2011 show that there were 1,784 molar pregnancies registered in England and Wales out of 700,000 live births. From past data, this equates to around one molar pregnancy for every 500 babies born. This means that for each obstetric unit molar pregnancies are quite rare, perhaps seeing one or two cases per year, but for the treatment centres they are quite common, with 1,200 patients registered and 120 treated at Charing Cross Hospital.


The symptoms of a molar pregnancy usually appear in the second or third month of pregnancy. The most common ones you are likely to experience are bleeding or the loss of some browny-red fluid. You may experience more severe morning sickness and vomiting than in a normal pregnancy.

If left untreated, a molar pregnancy may cause other problems such as a ‘large for dates’ uterus, high blood pressure and overactivity of the thyroid gland. However these problems are rare as the diagnosis is generally made within the first three months of pregnancy.

Diagnosis and treatment

A molar pregnancy is most commonly diagnosed after an abnormal ultrasound. The combination of a history of bleeding with the abnormal ultrasound is usually sufficient evidence to make a diagnosis.

The initial treatment for a molar pregnancy is to remove the tissue from the uterus with a surgical evacuation, which is also known as a 'D and C'. During this procedure the cervix is dilated in order to allow a suction curette to be inserted and remove the abnormal tissue. In some cases of partial molar pregnancy, the molar tissue may be removed with a medical evacuation where you will be given tablet treatment.

After the evacuation, some of the tissue is sent to the pathology laboratory for analysis to confirm the diagnosis of molar pregnancy.

In some cases where a miscarriage occurs or a termination is performed for another reason, the tissue sent to the laboratory may demonstrate that a molar pregnancy has occurred even when one was not suspected.

Follow up after a molar pregnancy

In normal pregnancies and in molar pregnancies, the cells that are created by fertilisation produce the hormone human chorionic gonadotrophin (hCG), which is detected in home pregnancy tests. When the egg is fertilised it starts to produce hCG and then as the pregnancy develops the trophoblastic/placental cells take over making hCG. After a molar pregnancy the level of the hCG gives an accurate measure of the number of abnormal cells left after evacuation. A rising hCG level after the evacuation indicates that further treatment is likely to be needed. Molar pregnancies carry a risk of developing into persistent trophoblastic disease which needs further treatment, most commonly with chemotherapy. Overall the risk of needing this treatment is about one in 10 after a complete molar pregnancy and one in 100 after a partial molar pregnancy.

All women in the UK who have had a molar pregnancy are enrolled in a national follow-up programme, where their levels of hCG are monitored. The gynaecology team that looks after you when the diagnosis of the molar pregnancy is made will do this. There are three centres for follow up of molar pregnancy in the UK: at Charing Cross Hospital in London, Weston Park Hospital in Sheffield and Ninewells Hospital in Dundee.

Your doctor will register you for follow up. Once registered all patients send blood or urine specimens every two weeks for measurement of the hCG level. The results are available one or two days after the sample is received. At Charing Cross the pattern of results for each molar pregnancy patient is analysed and you can check your results and treatment plans by calling. The duration of monitoring varies depending on the type of molar pregnancy and when the hCG levels return to normal.

Complete mole patients

If the hCG level returns to normal within 56 days of the evacuation, then the monitoring continues for a total of six months from the day of the evacuation. In those patients where the hCG level takes more than 56 days to get back to normal, the monitoring goes on for six months from the date of the first normal sample.

Partial mole patients

Following confirmation on review at Charing Cross, follow up begins with serum and urine tests every two weeks until hCG levels are normal. This is followed by one confirmatory normal urine sample after four weeks.

In both situations it is advised that you defer a further pregnancy until the end of the follow-up period. This is because a new pregnancy may mask evidence of a relapse of the illness, which can happen in a very small number of women.

If further treatment is needed

In most patients no further treatment is needed after the evacuation and the monitoring centre watches the hCG level fall back to normal and stay there. However, in approximately 10 per cent of patients who have had a complete molar pregnancy and one per cent of partial mole patients, treatment is needed.

The decision to start treatment is generally made on the pattern of the hCG levels following the evacuation.

While we generally do not do a further biopsy to prove it, if measuring samples indicates that the hCG level is rising and we decide to start treatment, we would regard you as having persistent trophoblastic disease, or choriocarcinoma, a very rare form of cancer. The good news is that this type of cancer is different from other forms of cancer and that the cure rate for patients developing this after a molar pregnancy is over 99 per cent. At Charing Cross the majority of patients who start treatment do so because their hCG level either starts to rise or stops falling and reaches a plateau. Some patients who have a high hCG level at four weeks after the evacuation are called in for treatment even if the value is not rising any further.

Treatments for persistent trophoblastic disease

There are three treatment possibilities for patients with persistent trophoblastic disease after a molar pregnancy.

The most frequent choice is chemotherapy. This approach is usually very simple, generally has few side effects, allows patients to retain their fertility and has a cure rate of over 99 per cent. More details on the practicalities of chemotherapy are given in the section below.

The second treatment option is to perform a second evacuation of the uterus with the aim of physically removing the residual disease. This can be curative in a minority of patients and help avoid the need for chemotherapy treatment. Recent reviews from Sheffield, Charing Cross and Holland suggest that second evacuations are best reserved for patients with no evidence of disease spread, an abnormality on the ultrasound of the uterus and an hCG level no higher than 1,500-5,000 IU/L. Currently we recommend that patients do not undergo a second evacuation if their hCG level is higher than 5,000 IU/L.

The third treatment option and that most rarely used is to treat the molar pregnancy by performing a hysterectomy. Prior to the introduction of chemotherapy treatment in the 1960s, this was the only treatment and proved to be curative in many cases. Treatment with hysterectomy has two disadvantages, the first is that it will of course prevent any further pregnancy and the second is that even after hysterectomy a number of women will need chemotherapy treatment as well as the surgery. Generally we rarely recommend hysterectomy as the main treatment after a molar pregnancy. However, some women may feel that hysterectomy is the right treatment for them due to their age, family plans being completed or other pre-existing gynaecological problems. In these cases we would recommend that patients are thoroughly reviewed at one of the treatment centres prior to undergoing surgery.


Chemotherapy is drug treatment which is used to kill the trophoblastic cells that are still trying to grow. The type of chemotherapy needed will depend upon the hCG level at the time of treatment and the results of other tests used to work out the prognostic score group.

Generally patients who need treatment after a documented molar pregnancy fall into the low risk treatment group and our policy at Charing Cross is for these patients to start chemotherapy treatment with the Methotrexate/Folinic acid combination.

The most usual treatment for this is chemotherapy with Methotrexate combined with folinic acid. This treatment is fairly low key and does not cause sickness or hair loss. The treatment is given over eight days: injections of Methotrexate are given on day one, three, five and seven, alternating with a tablet of folinic acid (an antidote to the chemotherapy) on days two, four, six and eight. After this period of treatment, there is a rest week off treatment and then the treatment starts again with another cycle of Methotrexate injections.

Generally the first week of treatment is given as an inpatient and then the subsequent cycles are given closer to home either by your GP or local oncology centre. Six weeks after leaving Charing Cross, you will normally come back for an outpatient appointment to review your progress and to get a further supply of Methotrexate injections to continue treatment.

The side effects that can occur with Methotrexate chemotherapy are generally quite mild, but can include sore eyes, mouth ulcers and occasionally abdominal or chest discomfort. The best way to minimise the chance of getting side effects or to minimise their severity is to try to take lots of fluids during treatment and to take the folinic acid tablets on time. If you do have problems let your medical team know and they may recommend some other approaches to cope.

hCG monitoring during chemotherapy

Whilst treatment is taking place, your serum hCG level should be monitored twice a week. The results from this are monitored at Charing Cross Hospital to check if the disease is responding well to treatment and the hCG level is falling appropriately. Of the patients who start with Methotrexate treatment, approximately one third will have to change to more intensive treatment. We are able to tell who needs to step up to more intensive treatment from the pattern of the hCG levels.

After chemotherapy treatment is completed

Chemotherapy is continued until the hCG level reaches normal and then for a further six weeks after that to kill off any residual cells. A further six weeks after completion of the whole course of chemotherapy, you will come back to the clinic at Charing Cross Hospital to be seen. At that visit your ultrasound and any other key tests are repeated. Usually these tests show that the problem has completely resolved and there will be no need to do any further investigations.

At this appointment we normally outline that there is a very high chance that the illness will have been cured already, but that there is a one to three per cent chance that it may flare up again. All patients then go into another hCG based follow-up programme to allow us to diagnose the rare cases of relapse early.

Normal life can be restarted and further hospital attendance is not usually required.

In many patients their periods will have already started again and nearly everybody’s will by six months after treatment. We suggest that you defer any future pregnancy for 12 months, that any form of contraception may be used and finally we advise you to avoid excess sun exposure for 12 months as it can produce patchy pigmentation in the skin.

Risks of molar pregnancy in future pregnancy

Women who have had one molar pregnancy do have an increased risk of developing another molar pregnancy in their next pregnancy. However this risk is still quite low: we would estimate it at around one in 100. Of the women who have had one molar pregnancy, 98 per cent will not have a molar pregnancy next time they are pregnant.

Advice for overseas patients

In the UK we are fortunate to have a centralised system for the care of molar pregnancy and choriocarcinoma, dealing with over 1,000 new patients with molar pregnancies each year and treating around 120. This system has allowed the optimisation of medical and nursing care for UK patients.

We are able to offer overseas patients help and support. If you wish, you can be treated as one of our patients at Charing Cross Hospital in London. You can find more information about this on our overseas visitors page.

The funding arrangements for this vary for patients from different countries.

We are happy to supply general treatment-related information to you and your medical team on request. We can help with queries regarding specific treatment questions for individual patients; generally these should be via your own doctor but can be direct if needed.