Sex-specific adverse neonatal outcomes and umbilical cord arterial ph at birth: a population-based cohort study

Background Biological sex may influence neonatal vulnerability to adverse perinatal outcomes, but sex-related differences in these outcomes remain underexplored. Male neonates may be more susceptible to perinatal asphyxia, metabolic acidosis, preterm birth, and morbidity, possibly due to sex-specific placental differences and inflammatory responses. Umbilical cord arterial pH (UApH) < 7.05 is used in Sweden to define neonatal acidemia, associated with poor outcomes. This study aimed to investigate the association between neonatal sex and adverse outcomes, focusing on UApH. Methods This retrospective multicenter cohort study used data from the Swedish Perinatal Revision South Register (1995–2015). The cohort included live-born, singleton, vaginal births. Neonatal and maternal data were extracted, and logistic regression models compared outcomes between male and female neonates, adjusting for maternal age, gestational age, and birth weight. Results Among 87 840 neonates, 51.6% were male. Male neonates had significantly higher adjusted odds of adverse outcomes compared with females: UApH < 7.05 (OR 1.18, 95% CI 1.07–1.30; P < 0.001), Apgar score < 7 at 5 min (OR 1.33, 95% CI 1.14–1.56; P < 0.001), CPAP use (OR 1.66, 95% CI 1.46–1.87; P < 0.001), NICU admission (OR 1.51, 95% CI 1.43–1.60; P < 0.001), hypoxic-ischemic encephalopathy (OR 2.24, 95% CI 1.29–3.90; P = 0.002) and central nervous system disease (OR 1.52, 95% CI 1.30–1.76; P < 0.001). Conclusions Male neonatal sex was associated with several adverse perinatal outcomes, including acidemia and neurological complications. These findings contribute to the understanding of sex-related differences in neonatal vulnerability and warrant further investigation. Trial registration Not applicable.