Vaginal lactate level predicts labor onset

NEW YORK (Reuters Health) - In pregnant women with suspected premature rupture of membranes (PROM), high levels of lactate in the vaginal fluid indicate that labor will begin within 24 hours, Swedish researchers report. Furthermore, testing for lactate can be performed easily at the bedside with results available in less than a minute.

The ability to predict labor onset could improve the outcome of women with suspected PROM, a condition in which the membranes rupture at about 37 weeks' gestation, but before labor begins. Symptoms include leakage of fluid, vaginal discharge, vaginal bleeding, and pelvic pressure. It affects about 10 percent of pregnancies.

If labor is expected to occur within the next 24 to 48 hours, then the best approach may be to just wait until labor begins. Conversely, if labor is not expected to begin until at least 48 hours later, then induction of labor is advisable.

The lactate found in the vaginal fluid of women with suspected PROM has been thought to arise from lactate released into the amniotic fluid by the fetus. However, recent evidence suggests that some of the lactate may also come from the myometrium, the smooth muscle lining the uterus.

In an earlier study, Dr. Eva Wiberg-Itzel, from the Soder Hospital in Stockholm, and colleagues showed that vaginal lactate levels vary considerably among women with suspected PROM.

They hypothesized that this variation may be related to differences in early myometrial activity. Thus, measuring lactate levels may provide some idea of when labor is about to occur.

To investigate, the researchers compared vaginal lactate levels to the time of labor onset in 179 women with suspected PROM. Lactate levels were determined at bedside by using a commercially available chemical test strip that provides results within 60 seconds.

The new findings appear in the medical journal BJOG.

When lactate levels were high, the average time from testing to the onset of labor was 8.4 hours, the report indicates. When lactate levels were low, the average time to labor was much longer -- 54 hours.

Labor began within 24 hours for 88 percent of women with high lactate levels and for 22 percent of those with low lactate levels.

After further analysis, the authors found that high lactate levels increased the odds of early labor onset (within 24 hours) by 13.5-fold.

"Provided that the results can be confirmed in independent populations, the simplicity of the method, with an answer after 60 seconds, makes the method very attractive in clinical practice," they conclude.

SOURCE: BJOG, December 2007.