Spontaneous and Induced Abortions The expulsion of a fetus from the uterus before it has reached the stage of viability (in human beings, usually about the 20th week of gestation). An abortion may occur spontaneously, in which case it is also called a miscarriage, or it may be brought on purposefully, in which case it is often called an induced abortion. Spontaneous abortions, or miscarriages, occur for many reasons, including disease, trauma, or genetic or biochemical incompatibility of mother and fetus. Occasionally a fetus dies in the uterus but fails to be expelled, a condition termed a missed abortion. Induced abortions may be performed for reason