What is the clinical evidence from this study?

Study design: Other. Population: null.

What does this research mean for the field?

Male fetuses are significantly more likely to have abnormalities in fetal heart rate tracings and experience adverse outcomes compared to female fetuses at term. Novelty: ClaimNovelty.NOVEL_FINDING. Consensus alignment: ConsensusAlignment.CHALLENGES_CONSENSUS.

What question did this study set out to answer?

The study aims to analyze differences in fetal heart rate tracings and adverse outcomes between female and male newborns delivered at term.

February 13, 2026

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

Key Result

null

Key Points

The study aims to analyze differences in fetal heart rate tracings and adverse outcomes between female and male newborns delivered at term.
Retrospective study of deliveries over 15 months
Inclusion of non-anomalous singletons delivered after 37 weeks
Blinded obstetricians interpreted fetal heart rate tracings during labor
Comparative analysis of neonatal and maternal adverse outcomes with adjusted odds ratios
Male fetuses had higher rates of severe late decelerations in fetal heart rate than females (aOR 5.25)
Increased cesarean deliveries due to non-reassuring fetal heart rates in males (aOR 1.21)
Composite neonatal adverse outcomes were significantly higher in male newborns (aOR 2.55)
Apgar scores below 7 at 5 minutes were notably worse for males (aOR 3.16)
Higher estimated blood loss was observed in mothers delivering males compared to females (aOR 1.51)

Structured PICO

Does male fetal sex increase abnormal fetal heart rate tracings and adverse outcomes in non-anomalous singletons delivered at > 37 weeks?

Population

3,165 non-anomalous singletons, delivered at > 37 weeks after labor, whose sex assignment at birth was either female or male (1,514 females [47.8%] and 1,651 males [52.2%])

Intervention

Male fetal sex

Comparator

Female fetal sex

Outcome

Fetal heart rate tracing (FHRT) and composite adverse outcomes (composite neonatal and maternal adverse outcomes [CNAO and CMAO])composite

Male fetuses are significantly more likely to have abnormalities of fetal heart rate tracings and adverse neonatal and maternal outcomes compared to female fetuses at term.

Abstract

Objective: To compare the fetal heart rate tracing (FHRT) and composite adverse outcomes among female versus male newborns delivered at term. Study Design: 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 min of labor. Composite neonatal and maternal adverse outcomes (CNAO and CMAO) were compared between the groups. Adjusted odds ratio (aOR) and 95% confidence intervals (CI) were calculated. Results: 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%), male. Obstetricians reviewed 358,620 minutes of FHRT. Compared to female, the FHRT among male 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 were categories I, II or III were similar. Cesarean delivery for non-reassuring FHRT was more common among male than female newborns (aOR 1.21; 95% 1.03-1.41). CNAO for male was significantly higher than female newborns (aOR 2.55; 95% CI 1.35-4.84). Apgar score 1,000 mL was significantly more likely among male than female newborns (aOR 1.51; 95% CI 1.09-2.08). Conclusion: Among singleton pregnancies delivered at term, male, compared to female, fetuses are significantly more likely to have abnormalities of fetal heart rate tracings, and adverse outcomes.

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