ABSTRACT
Surgery for birth defects helped create the specialty of pediatric surgery during the middle of the last century. The advances made against infectious disease mean that birth defects represent a leading cause of infant mortality. During the first trimester, organ morphogenesis predominates, while later trimesters are devoted to organ growth and maturation. While the model of first-trimester teratogenesis appears appropriate for many birth defects, certain anomalies appear to arise later as a result of fetal events, such as, amniotic band formation, intussusception, or vascular accident. Birth defect epidemiology involves the registration of anomalies by type. Birth defect epidemiology becomes difficult whenever the classification of defects is not uniform or straightforward. However, an equal challenge remains the counting of birth defects. This task is complicated by practical barriers to case ascertainment, the definition of stillbirth, and the effects of prenatal diagnosis and terminations. Prenatal diagnosis confounds birth defects surveillance in a number of ways.
