Birth defects range from minimal, such as birthmarks, and slightly mobility-impairing, such as amelia of the legs, to very serious, such as cerebral palsy, and incompatible with life, such as anencephaly.
Many birth defects result from genetic abnormalities. Others can arise from chance problems in fetal development (teratogenesis), which are sometimes caused by prenatal vitamin deficiencies or exposure to mercury and other harmful substances.
Some other birth defects: