A model for studying the pathogenesis and incidence of low-birth-weight infants.

A model is proposed for analyzing the many extextrinsic and intrinsic factors that might affect the incidence of low-birth-weight (LBW) infants (less than 2,501 g) adversely in populations of variable socioeconomic status (SES). The model provides for categorizing all mothers either into one of four broad categories of rinsic factors or into a normal group, free of all extrinsic factors. Application of the model in a prospective study of 972 infants showed that the incidence of LBW infants was low in normal pregnancies and significantly higher in the categories of extrinsic factors, that SES had a limited role in the birth of LBW infants, and that intrinsic factors had an almost negligible adverse effect if properly controlled.