Establishing Reference Serum Lactate Levels at 6 Hours Postpartum in Healthy Individuals: A Prospective Study

To investigate early postpartum (6-hr) lactate levels for both vaginal and cesarean births. Secondarily, to correlate the length of both stages of labor, active and second stage, with postpartum lactate levels for people with a vaginal birth.

Prospective observational cohort study.

Urban, level 3, nonacademic medical center with more than 5,000 births per year.

Convenience sample of 50 healthy, uninfected full-term peripartum individuals who had no pregnancy complications.

Two cohorts were observed at two time periods. Participants in Cohort A were scheduled for an induction of labor and Cohort B for cesarean birth. Venous lactate levels were collected on admission (baseline) and at 6 hr postpartum.

The mean early postpartum (6-hr) lactate level for all participants was 1.3 mmol/L (SD = 0.38 mmol/L). Forty-four of 48 retained individuals (92%) had mean lactate levels of 2 mmol/L or less at 6 hr postpartum. Four outliers (false positives) were observed, two in each cohort. For Cohort A, the length of active labor accounted for only 4% of the variance in postpartum lactate levels, and the length of the second stage of labor accounted for 22% of the variance.

Lactate level in early postpartum is often elevated above prelabor reference ranges. Clinicians could benefit from knowing when postpartum lactate is minimally influenced by childbirth. This evidence supports that the physiologic effects of labor are minimal at 6 hr postpartum, thus clinically useful. Current obstetric sepsis guidelines encourage early postpartum lactate levels to be collected on patients who screen positive for a serious infection and to reevaluate every 3 to 4 hr until vital signs and lactate level are normal. Lactate can be used to measure the severity of infection/sepsis and to trend the success of treatment measures.