To evaluate whether, at 37-39 weeks of gestation, delivery of a neonate with a birth weight that is 90% or greater for gestational age but less than 4,000 g is associated with increased composite maternal and neonatal morbidity. METHODS:This retrospective cohort study used U.S. Vital Statistics datasets for the years 2011-2013. Inclusion criteria were singleton pregnancies delivered at 37-39 weeks of gestation after labor in which the neonates were nonanomalous, and either appropriate for gestational age or large for gestational age (LGA) neonates with birth weights of less than 4,000 g (our threshold for macrosomia). The coprimary outcomes were composite maternal morbidity (any of the following: maternal transfusion, ruptured uterus, unplanned hysterectomy, admission to intensive care unit, or unplanned procedure) and composite neonatal morbidity (any of the following: Apgar score less than 5 at 5 minutes, assisted ventilation for more than 6 hours, seizure or serious neurologic dysfunction, significant birth injury or neonatal mortality). Multivariable Poisson regression models were used to calculate adjusted relative risk (aRR) and 95% CI.RESULTS: Among the 3.9 million women who met inclusion criteria, 1.3% delivered neonates who were LGA but nonmacrosomic. The rate of composite maternal morbidity was 53% higher women who delivered nonmacrosomic LGA neonate (6.27 vs 4.09/1,000 live births; aRR 1.40, 95% CI 1.25-1.56). This increased risk of composite maternal morbidity persisted in analyses stratified by diabetes. The rate of composite neonatal morbidity was 83% higher for nonmacrosomic LGA neonates (11.09 vs 6.07/1,000 live births; aRR 1.47, 95% CI 1.35-1.60) and persisted in analyses stratified by diabetes.CONCLUSION: At 37-39 weeks of gestation, delivery of a neonate with a birth weight that is 90% or greater for gestational age but less than 4,000 g is associated with increased composite maternal and neonatal morbidity.

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Since antepartum and intrapartum risk factors are poor at identifying women whose labor is complicated by shoulder dystocia, sonographic examination of the fetus holds promise. Though there are several measurements of biometric parameters to identify the parturient who will have shoulder dystocia, none are currently clinically useful. Three national guidelines confirm that sonographic measurements do not serve as appropriate diagnostic tests to identify women who will have shoulder dystocia with or without concurrent injury. In summary, biometric measurements of the fetus should not be used to alter clinical management with the aim of averting shoulder dystocia.