If you have polycystic ovaries your ovaries are slightly larger than normal ovaries and produce more small follicles than normal. This may be linked to an imbalance of hormones. Just under half of women with recurrent early miscarriages have polycystic ovaries; this is about twice the number of women in the general population.
Having polycystic ovaries is not a direct cause of recurrent miscarriage and it does not mean that you are at any greater risk of further miscarriages. Many women with polycystic ovaries and recurrent miscarriage have high levels of a hormone called luteinising hormone (LH) in their blood. Reducing the level of LH before pregnancy, however, does not improve your chances of a successful birth.
Prolactin is a hormone that prepares a pregnant woman’s breasts to produce milk. When a woman produces too much prolactin, this is known as hyperprolactinaemia. It is not yet clear whether this condition plays a role in recurrent miscarriage because the evidence is not clear and hence, currently, not conclusive.
If a serious infection gets into your bloodstream it may lead to a miscarriage. If you get a vaginal infection called bacterial vaginosis early in your pregnancy, it may increase the risk of having a miscarriage around the fourth to sixth month or of giving birth early. It is not clear, though, whether infections cause recurrent miscarriage; for this to happen, the bacteria or virus would need to be able to survive in your system without causing enough symptoms to be noticed. This rules out illnesses like measles, herpes, listeria, toxoplasmosis and cytomegalovirus (so you do not need to be tested for them if you have recurrent miscarriages).
Certain inherited conditions mean that your blood may be more likely to clot than is usual. These conditions are known as thrombophilia. They do not, though, mean that a serious blood clot will inevitably develop. Although thrombophilia has been thought to play some part in miscarriage, we do not yet know enough about how or why that is.
Some people have suggested that some women miscarry because their immune system does not respond to the baby in the usual way. This is known as an alloimmune reaction. There is no clear evidence to support this theory.
Diabetes and thyroid problems
Diabetes or thyroid disorders can be factors in single miscarriages. They do not cause recurrent miscarriage, as long as they are treated and kept under control.