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The loss of a much-wanted pregnancy can be devastating, and even more so if it happens again. This leaflet explains the definition of recurrent miscarriage and explores the tests and treatments that may be needed. The good news is that the eventual outlook is generally good as most couples who have experienced recurrent miscarriage go on to have a successful pregnancy.

A miscarriage is the loss of a baby before it has developed enough to survive, usually defined as before 24 weeks of pregnancy. In a miscarriage, this loss is spontaneous - in other words it hasn't been caused by medical or surgical means as is the case in an abortion (termination).

You can read about miscarriage in the separate leaflet called Miscarriage and Bleeding in Early Pregnancy.

What is defined as recurrent miscarriage varies between countries. In the UK, recurrent miscarriage is defined as three miscarriages in a row - ie the loss of three or more pregnancies before 24 weeks with no successful pregnancies in between. Guidelines in the USA and 2017 guidelines from Europe, however, suggest a diagnosis of recurrent miscarriage should be considered after the loss of two pregnancies, even if there has been a successful pregnancy in between the two miscarriages.

So it is confusing. If you have lost more than one baby, you probably don't care what the definition is, but the relevance is in the point at which you would be referred for tests. The traditional reasoning is that miscarriage is quite common (about one in five pregnancies end in miscarriage). So the chance of it happening again is quite high. Also the chances of finding the cause are quite low. Therefore there's a reasonably high chance that you would be subjected to tests and/or treatment for no gain. However, there seems to be a gradual shift in this thinking around the world towards a belief that earlier testing may be beneficial.

Recurrent miscarriage is not common. If you have had one miscarriage, the overwhelming odds are that it will not happen again. Working on the UK definition that recurrent miscarriage is three in a row, this happens to about 1 woman in 100. It is more common in older women, and the risk gets higher the older you are.

The simple answer is that quite often, nobody knows. In about half of cases, no cause is found after doing all the tests. In the other half, causes can be found and these include:

  • Abnormalities of the pregnant woman's womb (uterus). For example, long-standing infection or inflammation of the womb (endometritis), scarring of the lining of the womb, lumps (eg, fibroids or polyps) within it, or an unusual shape. Up to 19 out of every 100 women with recurrent miscarriage are found to have some type of abnormality of the womb.
  • A weak (incompetent) neck of the womb (cervix), also known as cervical insufficiency. The cervix normally only opens at the time of labour to let the baby come out. In some women the cervix is lax and opens too early. This can be a cause of late miscarriages.
  • Antiphospholipid syndrome (APS). This is an abnormality of the immune system which results in blood being more likely than normal to clot (a thrombophilia). This can lead to unwanted blood clots (called thromboses) forming within blood vessels. This can affect the blood supply to the placenta and developing baby. You can read more about it in the separate leaflet called Antiphospholipid Syndrome. About 5 to 20 out of every 100 women with recurrent miscarriage have APS. This is an important cause, particularly as it can be treated.
  • Other abnormalities of the clotting system of the pregnant woman. Inherited conditions, such as factor V Leiden deficiency, can also make blood more likely to clot and it may be that this contributes to recurrent miscarriage, although this is not known for sure.
  • Abnormalities of the genes or chromosomes of the parents. Chromosomes are the structures that contain genes with the genetic information that we inherit from our parents. If a baby (fetus) has abnormal chromosomes it may not develop properly and so the pregnancy will end. Many miscarriages can be caused by abnormal chromosomes but it is usually a one-off abnormality which has occurred in the baby. Sometimes the parents have mild abnormalities of their chromosomes, which do not affect the parent, but which, when combined or divided to create a baby, can cause a major chromosome problem for the developing baby. If this is the case then recurrent miscarriages can happen.
  • Hormone problems. Lack of hormones needed for pregnancy may be involved in some cases. A condition called hyperprolactinaemia, and low thyroid hormone levels (hypothyroidism), can affect hormones needed to maintain pregnancy. Low progesterone levels in the early stages of pregnancy may affect the way the developing baby embeds (implants) in the womb.
  • Lifestyle factors. It may be that factors such as smoking, drinking excessive alcohol regularly or being very overweight contribute to the likelihood of having miscarriages. Evidence is not yet clear how important these factors are.

As above, the timing of when you would be referred to a specialist for tests may depend on where you live. In the UK, this is usually only if you have had three miscarriages in a row, although in some cases it may be earlier, particularly if you are over the age of 35. In some other places, you may have tests after two miscarriages, and even if you have had a normal pregnancy in between the two miscarriages. Ideally you would be referred to a specialised recurrent miscarriage clinic.

The tests done may vary depending on your particular situation, your medical and family history and where you live, but can include:

  • An ultrasound scan to look for abnormalities of the womb (uterus) such as fibroids or an unusual shape. Further investigation may be required if the scan picks up any abnormality. In pregnancy an ultrasound scan may be helpful early on to check the neck of the womb for cervical insufficiency if you have had miscarriages late in previous pregnancies.
  • A blood test for antiphospholipid antibodies. Antibodies are proteins produced by the immune system that fight infection. In APS, abnormal antibodies are produced which attack a normal substance called phospholipid. If a blood test picks up these abnormal antibodies, you may or may not have APS, but you will need repeat tests, and tests for other abnormal (autoimmune) antibodies. Some people who do not have APS have the antibodies harmlessly for a short time. So a single positive test may not be relevant to recurrent miscarriage. See the separate leaflet called Antiphospholipid Syndrome for more information about the blood tests involved.
  • Blood tests for inherited abnormalities of the blood clotting system.
  • Blood tests for other medical conditions. You would normally have blood tests to check for thyroid conditions and diabetes. If you have symptoms or signs of other medical conditions which may be relevant then other specific hormone tests may be appropriate, although these would not be routinely done in all women.
  • Blood tests to look at the chromosomes of both parents.
  • Testing the chromosomes of a miscarried fetus in some cases, where this is possible.

This will depend whether a specific cause has been found after the tests described above. Possible treatments which may be advised include:

  • Both parents will normally be advised to have a think about any lifestyle factors which might be having an impact. The evidence is a little unclear about how important smoking, weight and alcohol intake are in contributing to recurrent miscarriage. However, it makes sense to address all these anyway as if any of them are an issue it may be relevant, and it will improve your general health.
  • If you have been found to have APS or certain other blood clotting problems then you will be advised to take blood-thinning medicines during future pregnancies - usually aspirin tablets and low molecular weight heparin injections.
  • Even if no cause has been found, some centres suggest blood-thinning medicines be taken in pregnancy but current evidence suggests this is not effective.
  • If a treatable abnormality of the womb has been found, an operation to correct it may reduce the risk of further miscarriage. For women with a weak neck of the womb (cervix), a stitch can be inserted in early pregnancy to keep it closed. This may help to prevent a miscarriage.
  • If either you or your partner are found to have abnormalities in your chromosomes, you would normally be referred to a specialist in genetics to advise you further. Some such couples may be given the option of pre-implantation genetic diagnosis. This essentially involves having in vitro fertilisation (IVF) with the idea that the embryo's genetics are tested before being put into the womb. Only genetically normal embryos would be used. This has obvious dilemmas, including cost, moral and religious beliefs and availability. Also the success rate of IVF may not be high enough to improve the chances of a successful pregnancy. So the evidence is weak that this is an effective option for couples having recurrent miscarriages who wouldn't otherwise be having IVF.
  • Some specialists have advised treating with a supplement of the hormone progesterone in early pregnancy, although the evidence is not clear about how beneficial this is. Further studies are ongoing to try to find out for sure.
  • Psychological support of some type may be helpful, as recurrent miscarriages are very distressing and are bound to affect you. It can put great strain on you both and your relationship. Some form of therapy may be helpful, such as counselling. It may also be useful to look at the resources of a support organisation, such as (in the UK) the Miscarriage Association.

In many cases no cause is found and no treatment has really convincingly been found to be effective in this scenario. So no treatment may be appropriate for many couples. It is still good news when no cause is found, however, as this makes it more likely that future pregnancies will be successful.

This also rather depends on the results of the tests you have had. If no cause has been found, the chances of having a normal pregnancy are very good. In this situation, 3 out of 4 women will go on to have a live born baby. However, this rate is less good if you are older and becomes less good the more the number of miscarriages you have experienced. If a genetic cause has been found, a specialist in genetics will be able to advise about future pregnancies. Once you have had tests, a specialist in recurrent miscarriage may be able to give you a better idea about the chances of a successful pregnancy in your individual situation. 

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