Female versus Male Fetuses—Variation in Fetal Heart Rate Tracing and Adverse Outcomes at Term

This study aimed to compare the fetal heart rate tracing (FHRT) and composite adverse outcomes among female versus male newborns delivered at term.The inclusion criteria of the retrospective study were non-anomalous singletons, delivered at ≥37 weeks after labor, whose sex assignment at birth was either female or male. The consecutive deliveries occurred over 15 months. Obstetricians-blinded to maternal characteristics and outcomes-interpreted the FHRT for the last 20 to 120 minutes of labor. Composite neonatal and maternal adverse outcomes (CNAO and CMAO) were compared between the groups. Adjusted odds ratios (aORs) and 95% confidence intervals (CIs) were calculated.Of the 5,160 deliveries during the study period, 3,165 (61.3%) met the inclusion criteria, and among them, 1,514 (47.8%) were females, and 1,651 newborns (52.2%) were males. Obstetricians reviewed 358,620 minutes of FHRT. Compared to females, the FHRT among males was significantly more likely to have severe late decelerations (aOR = 5.25; 95% CI: 1.16-23.83) or any severe decelerations (aOR = 1.21; 95% CI: 1.03-1.42). Whether the tracing was category I, II, or III, the incidence was similar. Cesarean delivery for non-reassuring FHRT was more common among male than female newborns (aOR = 1.21; 95% CI: 1.03-1.41). CNAO for male newborns was significantly higher than that for female newborns (aOR = 2.55; 95% CI: 1.35-4.84). Apgar score <7 at 5 minutes was the component of the CNAO that differed significantly (aOR = 3.16; 95% CI: 1.27-7.86). CMAO was also significantly higher for individuals who delivered male (9.3%) versus female (6.3%) newborns (aOR = 1.51, 95% CI: 1.16-1.98). Estimated blood loss ≥1,000 mL was significantly more likely among male than female newborns (aOR = 1.51; 95% CI: 1.09-2.08).Among singleton pregnancies delivered at term, male fetuses, compared to females, are significantly more likely to have abnormalities of FHRTs and adverse outcomes. · Male fetuses have more severe decelerations, including severe late decelerations, than females.. · Cesarean delivery for non-reassuring FHRT is significantly more common in male than female fetuses.. · CNAO is significantly more common in male than female fetuses.. · CMAO is significantly more common in male than female fetuses..