A pregnancy that ends before 20 weeks is considered a miscarriage. Miscarriages are common - they happen in roughly 1 in 5 pregnancies but the risk of miscarriage goes down a lot after the first 12 weeks of pregnancy. There are a variety of reasons that a pregnancy ends and there is no way to prevent a miscarriage. Miscarriage is not caused by stress, exercise, or sex. It is important to know the signs of a miscarriage and to know when to contact your maternity care provider. The links below provide more information about the causes, signs, and treatment of miscarriage.