To determine whether lactate levels were associated with maternal infection and infection-related outcomes in the antepartum, intrapartum, and early postpartum periods.

Retrospective, observational cohort.

Eleven hospitals from a single health system.

Women (N = 783) with at least one lactate and blood culture test for obstetric sepsis screening in the antepartum period (n = 154), intrapartum period (n = 348), and early postpartum period (n = 281) from January 2, 2018, to October 21, 2020.

We reported the proportion of participants with adverse outcomes by lactate cut points (≤2.0 and >2.0 mmol/L). We used logistic regression to model the association of infection-related outcomes with lactate levels and calculated receiver operating characteristic curves.

Lactate was associated with bacteremia among participants in the antepartum period (odds ratio [OR] = 1.60, 95% confidence interval [CI] [1.00, 2.56]) but not among participants in the intrapartum and early postpartum periods. Higher lactate levels were significantly associated with a composite measure of infection-related outcomes (OR = 1.41, 95% CI [1.14, 1.81]), with no differential association by antepartum, intrapartum, or early postpartum periods. Lactate levels were positively associated with intraamniotic infection in the antepartum period (OR = 1.57, 95% CI [1.06, 1.81]) but not in the intrapartum period. The receiver operating characteristic curve indicated that the lactate threshold of 2.0 mmol/L has poor sensitivity. Overall, participants in the antepartum period had lower lactate values than participants in the intrapartum and early postpartum periods.

Lactate levels were not consistently associated with infection-related measures across all periods. We suggest caution when interpreting lactate levels when sepsis is suspected.