Epidemiology of preterm delivery.

1. Defining prematurity as applying to LBW infants of less than 37 weeks' gestation and classifying those LBW infants of greater than 37 weeks as having IUGR provides an improved means of analyzing different risk factors. 2. In accordance with the method of D'Angelo and Sokol, risk factors have been assigned to the various disease entities and social factors (8). 3. There is a suspicion in some disease entities, such as chronic hypertension, that prematurity is of equal frequency to IUGR, and in others, such as renal disease, that IUGR may not be increased at all, at least in term or near-term gestation. A reevaluation of the relationship of some disease entities to IUGR and prematurity is needed, probably in the sophisticated manner of Hoffman et al (15).