The risk of low birthweight.

Descriptive analyses of birthweight for single live births in the United States during 1974, using birth certificate information, show that several factors are associated with a high incidence of low birthweight babies. Multivariate analyses were performed to determine correlates of low birthweight. When other factors are held constant, race not white, previous reproductive loss, short interpregnancy interval, out-of-wedlock birth, no prenatal care, and maternal age under 18 years or over 35 years each increase the risk of having an infant of low birthweight. High birth order and maternal education under 12 years of schooling were not consistent risk factors for low birthweight. Odds ratios are presented and the method for combining these, to estimate the risk for an individual mother having a low-birthweight infant, is illustrated.