Prediction of time to spontaneous onset of labour with lactate concentration in vaginal fluid in women with suspected preterm prelabour rupture of the membranes.

OBJECTIVE

To assess whether lactate determination in vaginal fluid is associated with and can predict onset of labour for women with suspected preterm prelabour rupture of membranes (PPROMs).

DESIGN

Prospective observational study.

SETTING

Labour ward at South General Hospital, Stockholm, Sweden. POPULATION/PARTICIPANTS: Women with suspected PPROMs at 20-36 completed weeks of gestation (n = 81).

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 MEASURE

Time from examination to spontaneous onset of labour (cervix > or =4 cm).

RESULTS

The median time between examination and onset of labour was 13.6 hours for those with a high (> or =4.5 mmol/l) lactate concentration and 1152 hours (i.e. 48 days) for those with a low (<4.5 mmol/l) lactate concentration. For a lactate threshold of 4.5 mmol/l, the likelihood ratio for positive test (LR+) was 12.6, and LR- was 0.14 for the outcome of spontaneous onset of labour within 48 hours.

CONCLUSIONS

A high lactate concentration in vaginal fluid is strongly associated with whether a woman with suspected PPROM will commence onset of labour within 48 hours. If confirmed, use of lactate ('LAC test') as a predictive test for onset of preterm labour may be an attractive tool in bedside obstetrics.