Association between fetal sex, birthweight percentile and adverse pregnancy outcome

INTRODUCTION: The objective was to evaluate the association between fetal sex and adverse pregnancy outcome, while correcting for fetal growth and gestational age at delivery. MATERIAL AND METHODS: Data from the Netherlands Perinatal Registry (1999‐2010) were used. The study population comprised all white European women with a singleton delivery between 25(+0) and 42(+6) weeks of gestation. Fetuses with structural or chromosomal abnormalities were excluded. Outcomes were antepartum death, intrapartum/neonatal death (from onset of labor until 28 days after birth), perinatal death (antepartum death or intrapartum/neonatal death), a composite of neonatal morbidity (including infant respiratory distress syndrome, sepsis, necrotizing enterocolitis, meconium aspiration, persistent pulmonary hypertension of the newborn, periventricular leukomalacia, Apgar score <7 at 5 minutes, and intracranial hemorrhage) and a composite adverse neonatal outcome (perinatal death or neonatal morbidity). Outcomes were expressed stratified by birthweight percentile (<p10 [small for gestation], p10‐90 [normal weight], >p90 [large for gestation]) and gestational age at delivery (25(+0)‐27(+6), 28(+0)‐31(+6), 32(+0)‐36(+6), 37(+0)‐42(+6 )weeks). The association between fetal sex and outcome was assessed using the fetus at risk approach. RESULTS: We studied 1 742 831 pregnant women. We found no increased risk of antepartum, intrapartum/neonatal and perinatal death in normal weight and large‐for‐gestation males born after 28(+0 )weeks compared with females. We found an increased risk of antepartum death among small‐for‐gestation males born after 28(+0 )weeks (relative risk [RR] 1.16‐1.40). All males born after 32(+0) weeks of gestation suffered more neonatal morbidity than females regardless of birthweight percentile (RR 1.07‐1.34). Infant respiratory distress syndrome, sepsis, persistent pulmonary hypertension of the newborn, Apgar score <7 at 5 minutes, and intracranial hemorrhage all occurred more often in males than in females. CONCLUSIONS: Small‐for‐gestation males have an increased risk of antepartum death and all males born after 32(+0) weeks of gestation have an increased risk of neonatal morbidity compared with females. In contrast to findings in previous studies we found no increased risk of antepartum, intrapartum/neonatal or perinatal death in normal weight and large‐for‐gestation males born after 28+0( )weeks.