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, pdiff < 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, pdiff < 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.