Ante partum determination of lactate in amniotic fluid

Abstract

Background: The present studies were conducted to investigate whether lactate determination in vaginal fluids, 'Lac-test', could be used as a diagnostic test for prelabour rupture of membranes (PROM). To derive the best cut-off value for a positive test and to asses weather lactate determination in vaginal fluid was associated with, and could predict, onset of labour for woman with suspect PROM.

Lactate concentration was measured with the commercially available Lactate ProTM an electrochemical test strip method which needs only 5ul of fluid to analyze the lactate concentration. The test was carried out bedside and the result was available after 60 seconds. The studies were made as prospective observational studies in labour ward at Söder hospital Stockholm years 2002-2003.

Paper I. Two hundred women with a history of suspect PROM after 34 weeks gestation were selected for determination of lactate concentrations in vaginal fluid. In 100 of these cases, actim PROM testTM were also analyzed. Sensitivity, specificity, positive and negative predictive values and Kappa indices were calculated. Results: A lactate concentration > 4.5 mmol/l was found to be the best cut-off value for a positive test. 'Lac-test' had a sensitivity of 86% (95% C.I. 77-96%), specificity 92% (95% C.I 84-99%), positive and negative predictive values of 92% and 87%, respectively. Likelihood ratio (LR) for a positive Lac-test was 10.75 and for a negative test 0. 15. The Kappa index for the 'Lactest' was 78%.

Paper II. One hundred and seventy nine women attending labour ward at Söder hospital with suspect PROM after 34 weeks gestation were selected for determination of lactate concentrations in vaginal fluid. Association between time to spontaneous onset of labour within 24 hours and 48 hours and lactate concentration in vaginal fluid was analyzed.

Results: The median time interval between examination and spontaneous onset of labour was 8.4 hours for those with "high" lactate (> 4.5 mmol/l) and 54 hours for those with "low" lactate concentrations (< 4.5 mmol/l). Among women with "high" lactate concentrations 76 (88%) started in labour within 24 hours, as compared with 20 (21%) for those with "low" lactate concentration, giving an Odds Ratio (OR) of 27.7; 95% C.I. 12-63.3.

Conclusion: Lactate determination is a valid test in cases with a history of suspects PROM. High lactate concentration (> 4.5 mmol/l) in vaginal fluid is strongly associated with, and can predict, woman with suspect PROM spontaneous onset of labour within 24 hours and 48 hours.