Introduction

The impact of birth defects on the affected individual, his or her family, and society in general is immense, encompassing mortality, morbidity, lost productivity, and medical care costs. In countries with low infant mortality, over 20% of infant deaths are due to birth defects (Shepard et al., 1989) and 18–30% of pediatric hospitalizations are due to congenital defects (Soltan and Craven, 1981; Weatherall, 1991). Risks of postnatal mortality, of prolonged hospitalization for children up to one year of age, and of neurologic abnormalities of children up to seven years of age are all increased in the presence of congenital abnormalities. Clearly, if there was a way to prevent the occurrence of birth defects, the benefits would be enormous.

This chapter first presents various ways in which birth defects are commonly defined and describes current knowledge of their frequency, as derived from various data sources including birth defect surveillance programs. The chapter then discusses our understanding of the etiology of birth defects from several perspectives and presents a case for addressing their prevention on primary, secondary, and tertiary levels.

Defining birth defects

There are numerous inconsistencies in defining birth defects, particularly in distinguishing between major and minor malformations. This lack of consistency has led to difficulties in tabulating congenital defects. The frequency of birth defects can vary greatly in different studies if, for example, one study includes all malformations, major and minor, while another excludes minor malformations.