Differences in the epidemiology of prematurity and intrauterine growth retardation.

Although both preterm (PT) and intrauterine growth retarded (IUGR) infants can have similar birth weights, they are known to show different neonatal and post-neonatal features. Newborns (n = 623) from the Guatemalan longitudinal study of nutritional supplementation during pregnancy were studied. There were 61 PT (less than or equal to 37 wk) and 173 IUGR (less than or equal to 10th percentile) infants. Simultaneous adjustment using the long-linear model showed that calorie and/or protein supplementation during pregnancy lowered the risk of PT (adjusted odd ratios (OR) = 0.52, 95%, CI = 0.40-0.77, and 0.43 CI = 0.36-0.59, respectively), but did not affect the incidence of IUGR. Low maternal head circumference and weight increased the risk of IUGR only (OR = 1.4, CI = 1.02-1.8 and 2.3 CI = 1.8-2.7, respectively). Male fetuses were at higher risk of both PT and IUGR. These data confirm the differential effect of maternal characteristics and nutritional supplementation during pregnancy on both PT and IUGR, and strongly suggest the need to include both gestational age and birth weight as outcome measures in epidemiological studies, thus avoiding the exclusive use of LBW (less than or equal to 2500 g).