Associations of intrapartum fever and clinical chorioamnionitis with obstetric anal sphincter injuries in term vaginal deliveries.

OBJECTIVE

To evaluate the association between intrapartum fever, clinical chorioamnionitis, and the risk of obstetric anal sphincter injuries (OASIS) in term vaginal deliveries, stratified by fever severity.

METHODS

This retrospective cohort study included all singleton, term (≥37 weeks), vertex vaginal deliveries at Galilee Medical Center between March 2020 and March 2025. The primary exposures were intrapartum fever-categorized as none, 38.0-38.9°C, and ≥ 39.0°C-and clinical chorioamnionitis, defined as maternal fever with at least one of the following: leukocytosis (>15 000/mm3), fetal tachycardia (>160 bpm), or foul-smelling amniotic fluid. The primary outcome was OASIS (third- or fourth-degree perineal tears) diagnosed postpartum by obstetricians. Multivariable logistic regression was used to adjust for potential confounders, including nulliparity, body mass index (BMI), birth weight, gestational age, delivery mode, mediolateral episiotomy, and second-stage duration.

RESULTS

Among 15 571 term vaginal deliveries, OASIS occurred in 93 (0.6%). The incidence increased with fever severity-83/15114 (0.6%) in afebrile women, 9/424 (2.1%) with moderate fever, and 1/21 (4.8%) with ≥39.0°C (P < 0.001). Clinical chorioamnionitis was also associated with OASIS (3.45% vs. 0.58%, P < 0.001). Independent risk factors for OASIS included nulliparity (adjusted odds ratio [aOR] 3.64, 95% confidence interval [CI]: 2.08-6.38), BMI <18.5 (aOR 24.90, 95% CI: 2.98-208.24), birth weight>4000 g (aOR 2.69, 95% CI: 1.40-5.18), intrapartum fever (aOR 2.57, 95% CI: 1.29-5.12), clinical chorioamnionitis (aOR 3.65, 95% CI: 1.27-10.47), and gestational age ≥ 41 weeks (aOR 1.91, 95% CI: 1.12-3.25).

CONCLUSION

Intrapartum fever and clinical chorioamnionitis independently increase OASIS risk in term vaginal births, showing a clear dose-response relationship with fever severity.