It can be heartbreaking to miscarry one baby after another. Each new pregnancy brings both hope and anxiety. And each new loss may be harder to bear, especially if you feel that time is running out. The experience can place great strain on even the strongest relationships. You and your partner might react differently from each other and that can cause great tension. Family and friends may find it harder to support you with each miscarriage; they may even think you’re getting used to loss and able to cope. And all the time there may be a sense that your life is on hold while you try – and try again – for a baby.
Recurrent miscarriage means having three or more miscarriages in a row. It affects about one in every hundred couples trying for a baby. Sometimes a treatable cause can be found, and sometimes not. But in either case, most couples are more likely to have a successful pregnancy next time than to miscarry again.
If you have had three miscarriages in a row, you should be offered tests to try to find the cause. This should happen whether or not you already have one or more children. Testing is not usually offered after one or two early miscarriages (up to 14 weeks) because these are often due to chance. But you might be offered tests after two early miscarriages if you are in your late 30s or 40s or if it has taken you a long time to conceive. If you had a late (second trimester) miscarriage, where your baby diedafter 14 weeks of pregnancy, you should be offered tests after this loss. For more information on late miscarriage, see our leaflet Late miscarriage:second trimester loss.
Why recurrent miscarriage happens
This section looks at things that increase your risk of recurrent miscarriage. It also looks at known and sible causes. Risk factors Your risk of recurrent miscarriage is higher if:
you and your partner are older; the risk is highest if you are over 35 and your partner over 40;
you are very overweight. Being very underweight may also increase your risk. Each new pregnancy loss increases the risk of a further miscarriage. But even after three miscarriages, most couples will have a live baby next time
Antiphospholipid syndrome (APS) This blood clotting problem is the most important treatable cause of recurrent miscarriage. It happens when your immune system makes abnormal antibodies that attack fats called phospholipids in your blood. This makes the blood more ‘sticky’ and likely to clot, which is whyAPS is sometimes called ‘sticky blood syndrome’. It is also known as ‘Hughes syndrome’ after the expert who named it. It is not clear why these antibodies cause miscarriage. They may stop the pregnancy embedding properly in the uterus (womb);or they may interfere with blood flow to the placenta, which supports the baby.
APS can also lead to problems in later pregnancy, including the baby not growing enough, pre-eclampsia or stillbirth. For more detail see our leaflet Antiphospholipid syndrome and pregnancy loss. Other blood clotting problems Some inherited blood clotting disorders can cause recurrent miscarriage, particularly after 14 weeks. These include factorV Leiden, factor II (prothromobin), gene mutation and protein S deficiency
Abnormal chromosomes The chromosomes in every cell of your body carry hereditary information in the form of genes. Everyone has 23 pairs of chromosomes, and 22 of these are the same in men and women. The 23rd pair are different because they determine gender. Men normally have one X and oneY chromosome and women two X chromosomes. A baby inherits half its chromosomes from each parent. About half of all miscarriages happen because the baby’s chromosomes are abnormal. This is not usually an inherited problem: it happens when the egg and sperm meet or soon after the egg is fertilised. The older you are the more likely this is to happen. Much less commonly (in less than five in one hundred couples with recurrentmiscarriage), one partner carries a chromosomal defect called a ‘balanced translocation’. This doesn’t cause a problem for the parent, but it can be passed on to the baby as an ‘unbalanced translocation’.
This means that some genetic information is duplicated and some is missing. We have a fact-sheet on balanced translocation. Cervical weakness (also known as ‘incompetent cervix’) Your cervix is a kind of ‘gateway’ between the uterus and vagina,which normally dilates (widens) during labour to allow the baby to be born. Some women – probably less than one in a hundred – have a weakness in the cervix that allows it to dilate too early. This is a known cause of late (second trimester) miscarriage.
Abnormally-shaped uterus Some miscarriages, particularly late ones, are thought to happen because the uterus (womb) has an abnormal shape.
It may be divided down the centre – known as ‘bicornuate’ or ‘septate’ uterus;or just one half of the terus may have developed – known as ‘unicornuate’ uterus. It is not clear from research how many women with recurrent miscarriage have these abnormalities. Also we don’t know how common these problems are in women who don’t miscarry. This makes it impossible to be sure that they cause miscarriage
Polycystic ovary syndrome (PCOS) Women with this condition have many small cysts in their varies. They also tend to have hormonal problems, including high levels of insulin and male hormone in the blood. It is these problems that are thought to play a part in recurrent miscarriage, but it is not clear how.
Some serious infections can cause or increase the risk of single miscarriages. These include toxoplasmosis, rubella, listeria and genital infection. But it is not clear whether infection plays a role in recurrent miscarriage. Immune problems Raised levels of uterine NK (uNK) cells may increase the risk ofrecurrent miscarriage, ut more research is needed to prove this. It’s important to know that these uNK cells are different from he NK cells found in general circulating blood (e.g. from your arm). Diabetes and thyroid problems Uncontrolled diabetes and untreated thyroid problems can cause miscarriage. But well-controlled diabetes and treated thyroid problems do not cause recurrent miscarriage.