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BACKGROUND Pregnant women are vulnerable to infection as their immune response is modulated. OBJECTIVE Serum biomarkers are used to diagnose and manage severe infections, but data on their utility during labor are limited. We compared lactate and procalcitonin levels in women with and without an intraamniotic infection to determine whether they are useful biomarkers for infection during labor. STUDY DESIGN We performed a prospective, observational cohort study of term, singleton pregnancies admitted with planned vaginal delivery in 2019 at a university medical center. The lactate and procalcitonin levels were determined during early labor, within 2 hours following delivery, and on postpartum day 1. Women with an intraamniotic infection in addition had their lactate and procalcitonin levels determined following an intraamniotic infection diagnosis. Samples were processed immediately in the hospital clinical laboratory. The primary outcome was the mean lactate level following delivery. The secondary outcomes were the lactate and procalcitonin levels at other time points. Comparisons based on infection status were performed using multivariate linear regressions. RESULTS A total of 22 women with intraamniotic infection and 29 uninfected women were included. The mean early labor lactate level (1.47 vs 1.49 mmol/L) and mean procalcitonin level (0.048 vs 0.039 ng/mL) did not differ and were normal in the uninfected and intraamniotic infection groups. The mean lactate level was highest following delivery for women in both the uninfected and intraamniotic infection groups (2.00 vs 2.33 mmol/L; adjusted P=.08; 95% confidence interval, 0.98–1.53). The lactate level returned to normal by postpartum day 1 and did not differ significantly based on the infection status at any time point in the adjusted models. The procalcitonin level following delivery was higher among women with vs without an intraamniotic infection (0.142 vs 0.091 ng/mL; adjusted P=.03). The procalcitonin level rose further in both the intraamniotic infection and uninfected groups on postpartum day 1 (0.737 vs 0.408 ng/mL; adjusted P=.05). CONCLUSION The lactate level is not significantly elevated in pregnant women with an intraamniotic infection above the physiological increase that is observed in women without infection at delivery. The procalcitonin level is elevated at delivery in women with an intraamniotic infection and warrants further investigation as a peripartum infection marker.