Classification schemes of small-for-gestational age and type of intrauterine growth retardation and its implications to early neonatal mortality.

Classification of small-for-gestational age (SGA) and pattern of intrauterine growth retardation (IUGR) and their relationship to early neonatal mortality (first 3 days) were studied in a population of 9201 full-term infants in a maternal and child center in Mexico City. SGA infants were classified on the basis of two methods: one, using the tenth percentile of a birth weight (BW) by gestational age reference growth distribution, and the other, using a cut-off point of birth weight of 2900 g. Crown-heel length (CHL) and Rohrer's ponderal index (PI = BW/CHL3) were used to classify patterns of proportionate and disproportionate IUGR. Overall, infants classified as SGA and type of IUGR had an increased risk of death in comparison to full-term appropriate-weight infants. IUGR proportionate infants with short CHL had a significantly greater mortality than disproportionate IUGR infants with normal CHL. A slightly but not significantly greater mortality was observed for IUGR disproportionate versus proportionate using PI regardless of the method of SGA used. The combination of misclassification for SGA and for type of IUGR were examined relative to the availability of gestational age and the uses of data for clinical management versus research. It is concluded that hospitals may tolerate misclassification of SGA but should pay close attention in assessing the pattern of IUGR when evaluating the mortality of newborn term infants.