Male infants are at higher risk of neonatal mortality and severe morbidity.

BACKGROUND: While a male infant is usually born with a higher birthweight than his female counterpart, he is more at risk of variety of adverse perinatal outcomes. Indeed, throughout life, females exhibit a marked survival advantage compared to males. The aetiology for such pertinent sex disparity remains unclear and is likely multifactorial. AIMS: The aim of this study was to investigate obstetric and perinatal outcomes by infant sex from 28 weeks in a contemporary, large Australian birth cohort. MATERIALS AND METHODS: A 14-year retrospective cohort study of 130 133 births over 28 weeks gestation from a single tertiary centre. RESULTS: Male infants had overall higher rates of neonatal mortality (0.12% vs 0.06%, P < 0.001) and severe neonatal morbidity (12% vs 9.1%, P < 0.001) (adjusted odds ratio (aOR) 1.41, 95% CI 1.35-1.47). The odds of overall perinatal mortality (stillbirth and neonatal death) were higher for male infants (aOR 1.30, 95% CI 1.08-1.56). The difference in severe neonatal morbidity when stratified by gestational age at birth only remained significant from >35 weeks gestation. Regardless of infant sex, rates of neonatal mortality and morbidity were lowest at 39 weeks gestation. Rates of preterm birth and operative birth were also higher for male infants. CONCLUSIONS: Our study demonstrates significant disparities in clinical outcomes by infant sex with males at a disadvantage to female infants.