How Should We Interpret Lactate in Labour? A Reference Study

Objective To investigate maternal lactate concentrations in labour and the puerperium. Design Reference study. Setting Tertiary obstetric unit. Population 1279 pregnant women with good perinatal outcomes at term. Methods Electronic patient records were searched for women who had lactate measured on the day of delivery or in the following 24 hours, but who were subsequently found to have a very low likelihood of sepsis, based on their outcomes. Main outcome measures The normative distribution of lactate and C-reactive protein (CRP), differences according to the mode of birth, and the proportion of results above the commonly used cut-offs (>= 2 and >= 4 mmol/l). Results Lactate varied between 0.4-5.4 mmol/l (median 1.8 mmol/l, interquartile range [IQR] 1.3-2.5). It was higher in women who had vaginal deliveries than caesarean sections (median 1.9 vs. 1.6 mmol/l, p(diff) < 0.001), demonstrating the association with labour (particularly active pushing in the second stage). In contrast, CRP was more elevated in women who had caesarean sections (median 71.8 mg/l) than those who had vaginal deliveries (33.4 mg/l, p(diff) < 0.001). In total, 40.8% had a lactate >= 2 mmol/l, but 95.3% were <4 mmol/l. Conclusions Lactate in labour and the puerperium is commonly elevated above the levels expected in healthy pregnant or non-pregnant women. There is a paucity of evidence to support using lactate or CRP to make decisions about antibiotics around the time of delivery but, as lactate is rarely higher than 4 mmol/l, this upper limit may still represent a useful severity marker for the investigation and management of sepsis in labour.