AN ANALYSIS OF BIRTH-WEIGHT BY GESTATIONAL-AGE USING A COMPUTERIZED PERINATAL DATA-BASE, 1975-1992

Objective: To develop birth weight-for-gestational age nomograms based on a computerized perinatal data base collected prospectively from 19 75-1992. Methods: Using information from over 60,000 singleton deliver ies (January 1975 through October 1992) at the Metro-Health Medical Ce nter in Cleveland, Ohio, standard curves for normal birth weights were computed. Nomograms were developed for the overall population and for subgroups determined by factors known to affect fetal growth, includi ng sex, race, smoking status, and gestational diabetes. The nomograms included the tenth, 50th, and 90th percentiles of birth weights for 24 -44 weeks' gestation. Gestational age was based on clinical obstetric estimates confirmed by Dubowitz assessment of the neonate. In addition , third-order regression models were developed to predict median birth weight using gestational age. These models were validated using deliv ery data for the months of November and December, 1992, which were not included in model development. Results: The most significant predicto rs of median birth weight were the first-, second-, and third-order ge stational ages, which explained over 80% of the total variation in bir th weight. Other significant factors influencing birth weight included infant gender, maternal race, parity, smoking, and diabetes status. A mong the marginally significant factors influencing birth weight were pay status and maternal age. In general, before 33 weeks' gestation, t here were few differences in the birth weight percentiles of various g roups except for those with diabetes; infants of diabetic women exhibi ted greater birth weights as early as 26 weeks' gestation. Conclusions : Considering the large size of the data base and the diverse backgrou nd of the study population, we believe that these nomograms provide us eful norms of birth weight for an indigent urban population. These nor ms enhance the obstetrician's and neonatologist's ability to identify true cases of retardation or acceleration of intrauterine growth. Simp le mathematical models provide easy calculation of the median birth we ights for 24-44 weeks while adjusting for many confounding factors.