Most pregnancies end happily with the birth of a healthy baby.
However, about 10 to 15 percent of pregnancies end in a premature delivery or miscarriage during the first 20 weeks. Usually, a miscarriage happens because the pregnancy was not developing normally. There is no way of knowing exactly what causes a miscarriage, but chances of miscarriage are higher for women who smoke, are seriously ill, or have pelvic infections. Signs of miscarriage include bleeding from the vagina and abdominal cramping. Along with blood, bits of the uterine lining may be passed.