Adjustment of birth weight standards for maternal and infant characteristics improves the prediction of outcome in the small-for-gestational-age infant

OBJECTIVE: Birth weight is a function of gestational age. Various maternal and infant characteristics also affect birth weight. This study sought to adjust for these factors to better define abnormal growth. STUDY DESIGN: Maternal and infant characteristics from normal pregnancies were correlated with birth weight. A formula was developed and applied to a second group in which we compared perinatal outcomes in normally grown infants with those who were small for gestational age. We compared outcomes between small-for-gestational-age infants defined by the formula with those defined by conventional tables. RESULTS: Infants defined by the formula as small-for-gestational-age were more likely to have morbidity and mortality than those who were normally grown (p < 0.001). Small-for-gestational-age infants defined by the formula had more deaths and adverse outcomes than those defined by gestational age. CONCLUSION: Adjusting birth weight standards for maternal and infant characteristics may improve the prediction of adverse outcomes.