New research to be published in BJOG: An International Journal of Obstetrics and Gynaecology has found that the 'Lac-test', a tool which measures the lactate concentration in vaginal fluid, may be highly effective in predicting the onset of preterm labour in women with suspected preterm prelabour rupture of membranes (PPROM). The study found that in such women, a high lactate concentration in vaginal fluid is strongly associated with the onset of labour within 48 hours.
While previous studies have found an association between high lactate concentration in vaginal fluids and rupture of membranes in pregnancies of 34 weeks gestation and more, this is the first time that an association has been found between lactate concentration and spontaneous onset of labour in women before 34 weeks. Prediction of spontaneous onset of labour is even more valuable in such preterm pregnancies, as antenatal steroids can be administered to improve the development of fetal organ systems, and women can be referred to specialist care services.
In this study, researchers at the Karolinska Institute Söder Hospital in Stockholm, Sweden, examined women in the labour ward with suspected PPROM between April 2002 and March 2004. The study included 86 women with singleton pregnancies of 20 to 36 weeks gestation. Lactate concentrations were analysed from samples of vaginal fluid.
The key findings indicate that high lactate concentrations are strongly associated with the spontaneous onset of labour within 48 hours. Among 23 women with high lactate concentrations of ≥4.5 mmol/l (a positive 'Lac-test'), 87% had spontaneous onset of labour within 48 hours. In 58 women with low lactate concentrations of ≤4.5 mmol/l (a negative 'Lac-test'), only 5% had spontaneous onset of labour within 48 hours. The median time between examination and onset of labour was 13.6 hours for those with a high lactate concentration, and 48 days for those with a low lactate value.
Preterm prelabour rupture of membranes (PPROM) is defined as rupture of the fetal membranes prior to onset of labour in a patient who has a gestational age of less than 37 weeks. PPROM accounts for one-third of all preterm births, and is associated with risks of preterm delivery and substantially increased risks of perinatal morbidity and mortality. An accurate diagnosis of PPROM is critical for the baby's health and survival. Traditionally, doctors have relied on factors such as visible amniotic fluid to diagnose PPROM, but have lacked a clear clinical marker to predict the onset of preterm labour.
Lead author, Dr. Eva Wiberg-Itzel, from the Department of Clinical Science and Education at the Karolinska Institute, said "The diagnosis of ruptured membranes is easy when there is an obvious leakage of amniotic fluid, but more difficult when the leak is scanty or intermittent. Traditional diagnosis of PPROM has relied on a combination of factors, including the woman's history, pooling of amniotic fluid in the vagina, microscopic examination of the vaginal fluid and/or biochemical tests.
"Thanks to this new method, a reliable diagnosis of PPROM could be made. We believe that the 'Lac-test' adds important information in clinical practice."
Prof. Philip Steer, BJOG editor-in-chief, said "Lactate determination seems promising as a tool to predict the onset of preterm labour in women with suspected PPROM. A positive 'Lac-test' is more strongly associated with spontaneous onset of labour than visible amniotic fluid.
"If these findings can be confirmed by further studies, the 'Lac-test' may be an important advance in the clinical management of suspected PPROM. A more reliable diagnosis of PPROM could help doctors determine when to keep women in hospital, and improve the timing of antenatal steroid therapy."
BJOG: An International Journal of Obstetrics and Gynaecology is owned by the Royal College of Obstetricians and Gynaecologists (RCOG) but is editorially independent and published monthly by Wiley-Blackwell. The journal features original, peer-reviewed, high-quality medical research in all areas of obstetrics and gynaecology worldwide. Please quote 'BJOG' or 'BJOG: An International Journal of Obstetrics and Gynaecology' when referring to the journal.
For more information, please contact the RCOG press office on 020 7772 6446 or 020 7772 6357.
Wiberg-Itzel E, Pettersson H, Cnattingius S, Nordstrom L. Prediction of time to spontaneous onset of labor with lactate concentration in vaginal fluid in women with suspected preterm prelabour rupture of membranes. BJOG 2009; DOI: 10.1111/j.1471-0528.2008.02017.x.