Selective reuction (or fetal reduction) is the practice of reducing the number of fetuses in a multifetal pregnancy (i.e. those involving more than one fetus). With selective reduction, a specific fetus or fetuses are "selected" for termination, usually after a congenital defect has been identified. Prenatal diagnostic testing may be used to determine which of the fetuses has a greater chance of chromosomal defect or genetic disease. Those fetuses are then targeted in selective reduction because of the probability of their health being inferior to that of the others.