Purpose of investigation: Studies on umbilical cord blood for determination of lactate indicate that high levels seem to be correlated to foetal metabolism for anaerobic glycolysis taking place in oxygen-deprived tissues of the foetus. These findings may be of particular-deprived clinical importance when foetal distress or foetal hypoxemia is caused by perinatal events.
Methods: The maternal and foetal heart rates, acid-base values measured and the outcome of 94 pregnancies complicated by intrapartum foetal asphyxia have been reviewed, and the maternal and foetal acid-base and lactate levels during the course of labour and at delivery were studied in patients with evidence of metabolic acidosis. Lactate concentrations were measured during labour and at delivery in blood samples obtained from the foetal presenting part and from the umbilical cord with the use of a rapid electrochemical technique. The foetuses were evaluated by means of the Apgar score, intrapartum cardiotocography, observation of the presence of meconium stained amniotic fluid, and clinical features of distress at birth.
Results: Evidence of clinical foetal distress was not related to the severity of the asphyxia. An increased lactate level was found in asphyctic infants and a clear correlation between lactic acidosis and foetal distress was documented. Low Apgar scores were observed in infants with moderate or severe asphyxia at delivery. Scalp lactate correlated significantly with umbilical artery lactate, but not with 1-min or 5-min Apgar scores. The lactate concentration was higher in cases of instrumental delivery compared to spontaneous delivery. No perfect correlation was found between lactate level and neonatal outcome but there were not a significant number of neonates with immediate complications. The rate of forceps delivery in the distress group was significantly higher than that of the healthy foetuses, so spontaneous labour was less frequently associated with foetal distress than instrumental delivery. In the distress group, severe variable decelerations were generally recorded in the second stage of labour. The incidence of neonatal Apgar score < or = 7 in neonates with abnormal baseline foetal heart rate (FHR) was higher than in those with severe variable decelerations, mild variable decelerations, and transient tachycardia. Duration of the active second stage of labour was significantly with the presence of foetal lactate at the time of crowning of the foetal head and the presence of lactate in umbilical arterial and vein blood at delivery. Expulsion time > or = 45 minutes, compared with shorter active second stage, and acidaemia at birth implied larger arterial-venous lactate differences. The presence of foetal lactate at crowning was also significantly associated with the level of umbilical arterial-venous lactate difference.
Conclusion: Lactate and pH values provide the best parameters to distinguish between asphyctic and normal newborns, with lactate having the most discriminating power. The prospective value of the discrimination functions derived from lactate and pH data is good when the foetuses are allocated into normal parameters but poor when an attempt is made to allocate the foetuses into pathologic ones, with a high false-negative rate. However, the discriminating ability is improved when pathologic foetuses are included into one single abnormal group. These results confirm the potential use of rapid foetal blood lactate measurements for the early diagnosis of intrapartum foetal distress.