Normal Range for Maternal Lactic Acid during Pregnancy and Labor: A Systematic Review and Meta-Analysis of Observational Studies.

OBJECTIVE:  This article systematically reviews the literature to establish the normal range of lactic acid in healthy pregnant women.

STUDY DESIGN:  Ovid MEDLINE, Embase.com, and Clinicaltrials.gov were searched to identify studies that reported maternal lactic acid in healthy pregnant women. Pooled aggregate means and two standard deviations for each time period were computed using the inverse variance weighting technique. Analyses were performed separately for 1st, 2nd, and 3rd trimesters, scheduled cesarean delivery, early labor, active labor, 2nd stage of labor, and delivery.

RESULTS:  Overall, 22 studies met the inclusion criteria. There were 1,193 patients, and 2,008 observations identified. All time periods had maternal venous lactic acid aggregate means and two-standard-deviation ranges less than 4 mmol/L. Outside of labor, all ranges were less than 2 mmol/L. All labor periods had a range higher than 2 mmol/L. While the pooled ranges were less than 4 mmol/L, many individual studies reported ranges > 4 mmol/L during labor.

CONCLUSION:  This meta-analysis suggests that venous lactic acid levels can be used as a screening tool in pregnant women just as the test would be used in nonpregnant women, except that elevations may be seen during labor, especially later in labor when there is maximal skeletal muscle contraction.