Placental contribution to lactate production by the human fetoplacental unit

Umbilical cord blood levels of lactate, base deficit, and pH were measured in 452 liveborn infants. In vigorous newborns, the mean umbilical arterial and venous concentrations of lactate were lowest with elective cesarean section, higher with cesarean section performed during labor, and highest with vaginal delivery (P less than .001). This suggests a rise in the fetal lactate level in response to labor. However, there was no concomitant increase in the mean umbilical arteriovenous lactate differences, indicating that both fetus and placenta increase their lactate production proportionately with labor. Depressed newborns had higher umbilical lactate levels than vigorous newborns irrespective of the method of delivery (P less than .001). Depressed newborns also had a higher mean umbilical arteriovenous lactate difference than vigorous newborns (P less than .001). This suggests that, under conditions that lead to neonatal depression, the fetus is the major source of the increased lactate produced, with a smaller contribution from the placenta. The fetal lactate level may be a good indicator of fetal stress in labor.