The aim of this page is to explain what a molar pregnancy is, how it is treated, and to answer the frequently asked questions.
What is a molar pregnancy?
A molar pregnancy happens when there are certain abnormalities in the fertilised egg at conception. The fertilised egg either never develops into an embryo (this is called a complete mole) or it develops abnormally and cannot survive (this is a partial mole).
In normal pregnancies, the fertilised egg contains 23 chromosomes from the father and 23 from the mother. In most complete molar pregnancies, the fertilised egg contains no maternal chromosomes and the chromosomes from the father’s sperm are duplicated. This means that there are 2 copies of chromosomes from the father and none from the mother. In this case, there is no embryo, amniotic sac or any normal placental tissue, instead, the placenta forms a mass of cysts.
In most partial molar pregnancies, the fertilised egg contains the normal 23 chromosomes from the mother, but double the chromosomes from the father, resulting in 69 chromosomes instead of the normal 46. This happens when chromosomes from the sperm are duplicated or when 2 sperm fertilise the same egg. In this case, there is some normal placental tissue among the cluster-like mass of abnormal tissue.
The embryo begins to develop, so there may be a foetus, or just some foetal tissue or an amniotic sac. Unfortunately, even if a foetus is present, in most cases it is so abnormal that it cannot survive.
It can be scary and upsetting to lose a pregnancy this way, but with treatment, you are unlikely to experience any long-term physical problems.
How common are molar pregnancies?
About 1 in every 1000 pregnancies is a molar pregnancy, your chances of having a molar pregnancy are higher if you:
- Are under the age of 20 or over 40 years old
- If you have had a previous molar pregnancy
- If you have had 2 or more miscarriages
How would I know if I had a molar pregnancy?
Almost all women with a complete molar pregnancy have vaginal bleeding in the first 3 months (first trimester). The symptoms usually mimic those of a miscarriage. Bleeding can start as early as 6 weeks into your pregnancy or as late as 12 weeks. You might also have severe nausea and vomiting, abdominal cramping, and abdominal swelling (your womb may grow more rapidly than usual). Women with a complete mole may have an unusually enlarged womb for the stage of the pregnancy.
If you do have a molar pregnancy, an ultrasound will show cysts that look like a cluster of grapes in your womb, and your levels of the pregnancy hormone human Chorionic Gonadotrophin (hCG) will be higher than normal.
What is the treatment for a molar pregnancy?
If you are diagnosed with a molar pregnancy, you will need a small operation to remove the abnormal tissue known as Evacuation of Retained Products of Conception (ERPC) or Surgical Management of Miscarriage (SMOM). These operations are done under general anaesthetic (while you are asleep).
All tissue taken during this operation will be examined in the hospital laboratory to confirm the diagnosis.
Registration of women with molar pregnancy
If the diagnosis of a molar pregnancy is confirmed, you will be registered with the Medical Oncology department of Charing Cross Hospital in London.
Charing Cross have an information leaflet available on their website, the web address is at the end of this page.
This registration is essential to monitor your blood hormone levels until they go back to normal and to advise you about future pregnancies.
Follow up of women with molar pregnancy
Specialists at Charing Cross Hospital will want to monitor your levels of the pregnancy hormone (hCG) over a period of weeks to make sure they are declining and there is no molar pregnancy tissue left. This follow up can continue for up to 1 year and usually consists of sending blood and urine tests to Charing Cross Hospital. Special envelopes will be provided.
If you have the disease known as Gestational Trophoblastic Disease (GTD), treatment with chemotherapy will be advised. This can delay your next pregnancy, but your doctor or nurse will discuss any concerns with you.
When can I try to get pregnant again?
You will need to wait for a year after your pregnancy hormone (hCG) levels return to zero before trying to get pregnant again, regardless of what kind of treatment you have received. If you become pregnant before then, your hCG levels would rise and it would be impossible for your practitioner to know whether abnormal tissue was growing back. Therefore, we would advise you to use condoms until your test results are back to normal.
The team at Charing Cross Hospital will advise you not to use hormonal contraception until your pregnancy hormone levels are back to normal.
A molar pregnancy does not affect your fertility or your ability to have a normal pregnancy, even if you have had chemotherapy. You are not at any increased risk for stillbirth, birth defects, premature delivery or other complications and the likelihood of having another molar pregnancy is only 1 to 2 in 100 cases.
In any pregnancy following a molar pregnancy, we will offer you an ultrasound examination within the first 12 weeks to make sure all is well.
How can I cope with my sense of fear and loss?
Having a molar pregnancy can be frightening and upsetting for both you and your partner. If you would like to discuss this please contact your GP, hospital doctor or nurse practitioner.
If you have any questions or concerns, please contact your GP or:
Gloucestershire Royal Hospital
Tel: 0300 422 5549
This line is open from 8:00am to 4:00pm, 7 days a week.
If you would like any further information or would like to talk to someone, please contact:
The Miscarriage Association c/o
17 Wentworth Terrace, Wakefield, Yorkshire WF1 3QW
Tel: 01924 200 799
Charing Cross Hospital
Listed below are 2 other Gloucestershire Hospital NHS Foundation Trust leaflets that you may like to read. Please ask your nurse or doctor for a copy.
- GHPI0131 Evacuation of Retained Products of conception (ERPC)
- GHPI1223 Surgical management of miscarriage