Macrosomic births in the united states: determinants, outcomes, and proposed grades of risk.

We describe maternal risk factors for macrosomia and assess birth weight categories to determine predictive thresholds of adverse outcomes. We analyzed linked live birth and infant death cohort files from 1995 to 1997 for the United States with the use of selected term (37-44 weeks of gestation) single live births to mothers who were US residents. We compared macrosomic infants (4000-4499 g, 4500-4999 g, and >5000 g infants) with a normosomic control group of infants who weighed 3000 to 3999 g. Maternal risk factors for macrosomia included nonsmoking, advanced age, married, diabetes mellitus, hypertension, and previous macrosomic infant or pregnancy loss. The risks of labor complications, birth injuries, and newborn morbidity rose with each gradation of macrosomic birth weight. Infant mortality rates increased significantly among infants weighing >5000 g. Although a definition of macrosomia as >4000 g (grade 1) may be useful for the identification of increased risks of labor and newborn complications, >4500 g (grade 2) may be more predictive of neonatal morbidity, and >5000 g (grade 3) may be a better indicator of infant mortality risk.