: spontaneous expulsion of a human fetus before it is viable and especially between the 12th and 28th weeks of gestation—compare abortion 1a
Spontaneous expulsion of an embryo or fetus from the uterus before it can live outside the mother. More than 60% are caused by an inherited defect in the fetus, which might result in a fatal abnormality. Other causes may include acute infectious disease, especially if it reduces the fetus's oxygen supply; abnormalities of the uterus that have physical or hormonal origins; and death of the fetus from umbilical-cord knotting. The main sign of impending miscarriage is vaginal bleeding.