Lack of progress in labour (dystocia) is one of the most commonly occurring problems requiring intervention during labour. In many industrialized countries labours are treated for dystocia by augmenting with oxytocin to accelerate or improve progress[2, 3]. However there is currently no accurate method for predicting at the onset of augmentation who will progress to a vaginal birth or who will require a cesarean section. In clinical practice, many labours deemed lacking in progress result in a normal vaginal birth. Conversely, women augmented for slow progress in labour may experience long painful labours that ultimately result in caesarean section.
Currently dystocia is diagnosed clinically by observing factors such as slowing of cervical dilation, slowing of descent and rotation of the fetal head, and changes in strength, duration and frequency of uterine contractions. In the absence of a clear and consistent definition or marker to guide decision making there is considerable variation in diagnosis and clinical practice. There is a need for improved diagnostic methods and decision making tools in the diagnosis of dystocia in order to reduce the high rates of labour intervention attributable to this condition.
Measurement of lactate in amniotic fluid of labouring women may be a surrogate biochemical marker for labour dystocia[6–9] based on the reasonable hypothesis that dystocia is partly due to lactic acidosis of myometrial tissue. Recent physiological studies on the effects of acidification of the uterus show human myometrium to be sensitive to changes in pH, and that accumulation of lactic acid in myometrium during contractions may reduce the strength of contractions[7, 11]. More recent studies of the acid–base balance of uterine tissue indicate that MCT 4 proteins, which appear to be activated when the myometrium is hypoxic, may be the mechanism by which lactic acid in myometrium is transported to the surrounding amniotic fluid.
If amniotic fluid lactate is relevant in the clinical management of dystocia, it is essential that a rapid and accurate test for amniotic fluid lactate is available. Although measurement of lactate using laboratory based spectrophotometric and fluorometric assays is possible this is not clinically useful in diagnosing dystocia due to time constraints in the clinical setting of active labour. The Lactate Pro is a small, portable hand held device used to process blood samples at the point of care which is relatively inexpensive. It has the potential to be used in rural and remote settings where laboratory technology may be unavailable due to costs and /or operator skill and has been found to be easy to operate and accurate[13, 14]. Manufacturer’s specifications indicate the Lactate Pro meter measures lactate concentrations in whole blood between 0.8 and 23 mmol/L and previous tests of reliability in amniotic fluid show minimal measurement error with a coefficient of variation of (1.7–3.0%). However, validation studies for use of the Lactate Pro to test lactate in amniotic fluid are not well described, and previous studies of amniotic fluid lactate not sufficiently powered to determine the utility of amniotic fluid lactate measurement for women in labour.
This report describes an assessment of a handheld meter (the Lactate Pro) for measuring amniotic fluid lactate, prior to conducting a large prospective study. The primary objectives of the pilot amniotic fluid lactate study were to assess the consenting processes for recruiting women to amniotic fluid lactate research and evaluate methods of amniotic fluid collection. We also aimed to determine the clinical aspects of relevant confounding factors in the measurement of lactate in amniotic fluid by contaminants, and determine the concordance between bedside measurement of lactate using the Lactate pro hand held meter and reference laboratory biochemical measurements.