- What is a molar pregnancy?
- What are the symptoms of a molar pregnancy?
- How is the diagnosis of molar pregnancy made?
- How is a molar pregnancy treated?
- Why is it important that the diagnosis of molar pregnancy is correctly made?
- How does the surveillance programme work?
- What is hCG and how is it measured?
- What is known about the cause of molar pregnancies?
- How common are molar pregnancies?
- Is molar pregnancy a type of cancer?
- How is the decision made on who needs further treatment after the evacuation?
- What are the usual treatments for persistent trophoblast disease after a molar pregnancy?
- What happens in chemotherapy treatment?
- What happens after the chemotherapy treatment is competed?
- Having had a molar pregnancy what are the risks in any future pregnancy?
- Where can I find more information about molar pregnancies and other forms of trophoblast disease?
A molar pregnancy occurs as a result of an abnormality when a sperm fertilises the egg. Despite the fertilised egg growing, dividing, and producing a positive pregnancy test, 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 have differences in their characteristics and the risk of needing further treatment.
In a complete molar pregnancy the mother’s genetic material from the ovum (egg) is lost at the time of fertilisation. When fertilization occurs it is with either one or two sperms and an androgenic (from the male only) fertilized egg is formed which develops as a complete molar pregnancy. In a complete molar pregnancy the embryo does not develop at all but the placental tissue grows quickly but it is very abnormal and forms lots of cysts.
If untreated a complete molar pregnancy would normally miscarry by 16 to 18 weeks gestational age, however in complete molar pregnancy the diagnosis is usually made earlier as a result of abnormal bleeding or with the initial booking ultrasound.
The other form of a molar pregnancy is a partial mole which 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 chromosomal (genetic) material from the ovum (egg) is retained but the egg is fertilized by two sperm. As the partial mole has the 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.
The symptoms of a molar pregnancy usually appear in the second or third month of pregnancy. The most common problems are bleeding or the loss of some browny-red fluid. Morning sickness and vomiting may be more severe than in a normal pregnancy.
If let untreated a molar pregnancy may cause other problems as a large for dates uterus, high blood pressure and over activity of the thyroid gland. However these problems are rare as the diagnosis is generally made within the first 3 months of pregnancy.
The diagnosis of molar pregnancy is most commonly made after an abnormal ultrasound. The combination of a history of bleeding with the abnormal ultrasound is usually sufficient for a surgical evacuation to be performed.
After the evacuation to confirm that the diagnosis is a molar pregnancy, some of the tissue is sent to the pathology laboratory for analysis.
In other cases when a miscarriage occurs or a termination is performed for some other reason, the tissue sent to the laboratory may demonstrate that a molar pregnancy has occurred, even when one was not suspected.
The initial treatment for a molar pregnancy is to remove the tissue from the uterus with an evacuation (‘D and C’). In this procedure the cervix is dilated in order to allow a suction curette to enter and then remove the abnormal tissue. In some cases of partial molar pregnancy, the molar tissue may be removed by a medical evacuation with tablet treatment used to empty the uterus.
There are a number of reasons why it is important that the diagnosis of molar pregnancy is correctly made. 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 1 in 10 after a complete molar pregnancy and 1 in 100 after a partial molar pregnancy. At present there is no accurate way of predicting immediately after the evacuation who will need further treatment, so it is the policy in the UK that all women who have had a molar pregnancy enter the surveillance programme.
In the UK all cases of molar pregnancy should be registered for hCG (pregnancy test hormone) based follow-up. 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.
Registration can be made by paper, email or online. Once registered all patients send blood or urine specimens for measurement of the hCG level that allows the activity of any residual molar tissue to be followed.
Samples are sent every two weeks and the results allow the team to continue to monitor the patients where the level is falling or to call in for treatment the minority where the level is static or rising.
In all cases of molar pregnancy and the other forms of trophoblastic disease the hCG level is important for making the diagnosis and for monitoring treatment. The abbreviation hCG is short for human Chorionic Gonadotrophin, the pregnancy test hormone that is detected in home pregnancy tests. In pregnancy (normal and molar) when the egg is fertilised it starts to make 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 and a rising hCG level after the evacuation is a pointer that further treatment is likely to be needed.
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 get pregnancy is approximately 1.5 times higher and for women aged over 45 the risk is 20-50 times higher than for younger women. 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 5 times higher than normal which works out as about a 1 in 100 chance of having a second molar pregnancy.
The figures for the UK in 2011 show that there were 1784 molar pregnancies registered in England and Wales and that there were 700,000 live births. From past data, this equates to around 1 molar pregnancy for every 500 babies born. This means that for each obstetric unit molar pregnancies are quite rare perhaps 1 or 2 cases per year, but for the treatment centres they are quite common with 1200 patients registered at Charing Cross and 120 treated.
If you have had a molar pregnancy, the majority of time the problem will disappear on its own and no further treatment is needed. A molar pregnancy on its own is not a form of cancer. For the approximately 15% of patients who have had a complete molar pregnancy and 1% of partial mole patients who go on to further treatment the situation is different. Whilst we generally do not do a further biopsy to prove it, once the hCG level is rising and the decision to start treatment is made we would regard these patients as having this very rare form of cancer. We refer to these patients as having persistent trophoblastic disease/choriocarcinoma, this new situation is defined in the medical text books and by the World Health Organisation (WHO) as a type of cancer. However the good news is that this type of cancer is completely different from the normal types of cancer and that the cure rate for patients developing this after a molar pregnancy is over 99%. For patients who have either choriocarcinoma after the birth of a baby or who have placental site trophoblastic tumour, these are also forms of cancer, which fortunately also have very high cure rates.
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% of patients who have had a complete molar pregnancy and 1% 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.
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.
There are three treatment options for patients with persistent trophoblastic disease after a molar pregnancy. The most frequent choice is to use chemotherapy. This approach is simple, generally has few side effects and allows patients to retain their fertility. It has a cure rate of over 99%, 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 them avoid the need for chemotherapy treatment. Reviews from the UK and the Netherlands 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 is by performing a hysterectomy. Prior to the introduction of chemotherapy treatment in the 1960s this was the only treatment and fortunately proved to be curative in many cases. Treatment with hysterectomy has two disadvantages, the first is that it will preclude any further pregnancy which may not be an issue for women who have decided that they have completed their families. The other is that even after a hysterectomy some women still require chemotherapy.
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 treatment with drugs to kill the trophoblastic cells that are still trying to grow. The type of chemotherapy needed will depend upon the hCG hormone level at the time of treatment and the results of other tests used to work out the prognostic score group.
Generally for patients who need treatment after a documented molar pregnancy, they 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.
This treatment is very gentle, it doesn’t cause hair loss or sickness. The Methotrexate chemotherapy injection is given as an intramuscular injection on the first day of treatment then followed by the folinic acid tablet the following day. This is then repeated 4 times for an 8-day course of treatment. After the 8 days there is a 6 day rest period and then the whole cycle of treatment continues again.
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 get problems let your medical team know and they may recommend some other approaches to cope with the problems.
Chemotherapy is continued until the hCG level reaches normal and then for a further 6 weeks after that to kill off any residual cells. A further 6 weeks after completion of the whole course of chemotherapy patients come back to the clinic at Charing Cross Hospital to be seen. At that visit their ultrasound and other key tests are repeated. Usually these tests show that the problem has completely resolved and that there will be no need to perform any further investigation.
At this appointment we normally outline that there is a very high chance that the illness will have been cured but that there is a 1-3% chance that it may flare up again. All patients subsequently go into a hCG based follow-up programme to allow us to detect any cases of relapse.
The other advice is that normal life can be restarted and that further hospital attendance is not usually required.
In many patients their periods will have already started again and nearly everybody does by 6 months after treatment. We suggest that any future pregnancy is deferred for 12 months, that any form of contraception may be used and finally to avoid excess sun exposure for 12 months as it can produce patchy pigmentation in the skin.
Women who have had one molar pregnancy do have an increased risk of developing another molar pregnancy when they are next pregnant. However this risk is still quite low, we would estimate it at around 1 in 100. Put more positively, of the women who have had one molar pregnancy 98 out of 100 will not have a molar pregnancy next time they are pregnant.
16. Where can I find more information about molar pregnancies and other forms of trophoblastic disease?
There is a lot of information on molar pregnancy and the other forms of trophoblastic disease. If you look at the links section it will take you through some patient friendly web sites and also some more technical ones with advice in our clinicians section. We also have a video of frequently asked questions here.