Association between lactate in vaginal fluid and time to spontaneous onset of labour from women with suspected prelabour rupture of the membranes

Abstract

Objectives To assess whether lactate determination in vaginal fluid is associated with, and can predict, onset of labour for women with suspected prelabour rupture of the membranes (PROM). Design Prospective observational study. Setting Labour ward at Soder Hospital, Stockholm, Sweden. Population Women with suspected PROM after 34 weeks of gestation, who later had spontaneous onset of labour (n= 179). Methods All women underwent a speculum examination and a test for determining lactate concentration in vaginal fluid. We used logistic regression to estimate the association between lactate concentration in vaginal fluid and time to onset of labour. Main outcome measures Time from examination to onset of labour (cervix ≥4 cm), within 24 hours and 48 hours. Results The median time interval between examination and spontaneous onset of labour was 8.4 hours for women with ‘high’ lactate (≥4.5 mmol/l) and 54 hours for those with ‘low’ lactate concentrations (<4.5 mmol/l). Among 86 women with high lactate concentrations, 76 (88%) had started labour within 24 hours compared with 20 of 93 (22%) women with low lactate concentrations (OR 27.7, 95% CI 12.2–63.3). After checking for the effect of visible amniotic fluid, the corresponding odds were still substantially increased (OR 13.5, 95% CI 5.3–34.3). Conclusions High lactate concentration (≥4.5 mmol/l) in vaginal fluid can be used to predict whether a woman with suspected PROM will commence spontaneous onset of labour within 24 or 48 hours.