Homeostasis of fetal lactate metabolism in late pregnancy and the changes during labor and delivery.

Electrochemical enzymatic measurements of whole blood lactate concentrations were performed in 110 deliveries. In the majority of uncomplicated vaginal deliveries and of elective cesarean sections cord blood levels were higher than maternal concentrations and, as indicated by a positive arterio-venous difference for the cord vessels, lactate is originating in the fetus. In cases with clinical signs of fetal distress production of lactate due to anaerobic glycolysis is markedly increased. Differently from some other studies with uncomplicated vaginal deliveries, maternal lactate concentrations remained below fetal levels in almost 80%, which is explained by a conservative management of the second stage of labor with active pushing being restricted to the final phase of expulsion. The question whether also in late pregnancy the undisturbed human fetus in utero produces lactate or makes use of placental lactate as a substrate for its oxidative metabolism - as has been shown for some animal species - cannot be answered from the presently available evidence.