Birth defects are the abnormalities in structure,function or metabolism of embryonic or fetal development.They are the main cause of early abortion,stillbirth,perinatal mortality,infant mortality and congenital disabilities.Birth defects affect not only the health and life quality of children,but also the population quality of the whole country.This paper reviews the current epidemic situation and possible causes and risk factors of birth defects.It also expounds on the importance of epidemiological study o...