Spontaneous Abortion is another term for miscarriage, in which a mother loses the fetus before the 20th week of pregnancy. Symptoms include heavy bleeding and cramping as the fetus is passed out of the mother’s uterus. In spontaneous abortion, the fetus dies of natural causes due to abnormal development of the fetus or placenta. Substance abuse, medication use, or infection in the mother can also cause a miscarriage. Most miscarriages occur in the first trimester of pregnancy.