Low-grade intrapartum fever and operative vaginal delivery: A retrospective cohort study

To evaluate the association between low-grade intrapartum fever (37.5-37.9°C) and obstetric and neonatal outcomes, and to compare its clinical significance with that of overt intrapartum fever (≥38.0°C).

This retrospective cohort study included nulliparous women with singleton pregnancies who delivered over a 7-year period at a single tertiary academic medical center. Participants were categorized according to maximal intrapartum maternal temperature into three groups: low-grade intrapartum fever (37.5-37.9°C), overt intrapartum fever (≥38.0°C), and afebrile controls. The primary analysis focused on outcomes associated with low-grade fever compared with afebrile women, while the intrapartum fever group was included as a reference to contextualize the magnitude of risk. The primary outcomes were operative vaginal delivery (OVD) and intrapartum cesarean delivery (CD), analyzed separately. Secondary outcomes included selected neonatal outcomes, including a 5-minute Apgar score < 7. Multivariable logistic regression was performed to adjust for potential confounders.

A total of 15,093 women met inclusion criteria, including 1,294 (8.6%) with low-grade intrapartum fever, 934 (6.2%) with overt intrapartum fever (≥38.0°C), and 12,865 (85.2%) afebrile controls. Compared with afebrile controls, women with low-grade fever had higher rates of OVD (27.0% vs. 17.0%, p < 0.001), although rates remained lower than those observed in the overt fever group (31.0%, p < 0.001). Cesarean delivery rates were increased only among women with overt intrapartum fever and were comparable between the low-grade fever and afebrile groups. Low-grade fever was also associated with a higher rate of 5-minute Apgar score < 7 compared with controls (0.9% vs. 0.4%, p = 0.034). After adjustment for maternal age, diabetes mellitus, hypertensive disorders, gestational age at delivery, labor induction, epidural analgesia, and neonatal birthweight, low-grade intrapartum fever remained independently associated with increased risk of OVD (adjusted OR 1.54, 95% CI 1.35-1.76) and 5-minute Apgar score < 7 (adjusted OR 2.50, 95% CI 1.28-4.89).

Low-grade intrapartum temperature elevation was independently associated with increased operative vaginal delivery and low 5-minute Apgar score. These findings suggest that subfebrile temperature elevations may identify a more complicated intrapartum course, although the temporal relationship between temperature elevation and labor progression or delivery mode, and therefore causality, cannot be established.