Often, in spite of careful investigations, the reasons for recurrent miscarriages cannot be found. However, if you and your partner feel able to keep trying, you still have a good chance of a successful birth in future. There are a number of things that may play a part in recurrent miscarriage. It is a complicated problem and more research is still needed.
Some of the possible causes are listed below.
The older you are, the greater your risk of having a miscarriage. The more miscarriages you have had already, the more likely you will be to have another one.
For around three to five in every 100 women who have recurrent miscarriages, they or their partner have an abnormality on one of their chromosomes (the genetic structures within our cells that contain our DNA and the features we inherit from our parents). Although such abnormalities may cause no problem for you or your partner, they may sometimes cause problems if passed on to your baby.
An abnormality in the embryo is the most common reason for single miscarriages. However, the more miscarriages you have, the less likely this is to be the cause of them, unless you or your partner are carriers of a genetic condition (balanced translocation).
Antibodies are substances produced in our blood in order to fight off infections. Around 15 in every 100 women who have had recurrent miscarriages have particular antibodies, called antiphospholipid antibodies (aPL), in their blood; fewer than two in every 100 women with normal pregnancies have aPL antibodies. Some people produce antibodies that react against the body’s own tissues; this is known as an autoimmune response and it is what happens to women who have aPL antibodies. If you have aPL antibodies and a history of recurrent miscarriage, your chances of a successful pregnancy may be only one in ten.
It is not clear how far major irregularities in the structure of your womb can affect the risk of recurrent miscarriages. Estimates of the number of women with recurrent miscarriage who also have these irregularities range from two out of 100 to as many as 37 out of 100. Women who have serious anatomical abnormalities and do not have treatment for them seem to be more likely to miscarry or give birth early. Minor variations in the structure of your womb do not cause miscarriages.
In some women the entrance of the womb (the cervix) opens too early in the pregnancy and causes a miscarriage in the third to sixth month. This is known as having a weak (or ‘incompetent’) cervix. It is overestimated as a cause of miscarriage because there is no really reliable test for it outside of pregnancy.