Carbohydrate and lipid metabolism during human labor: free fatty acids, glucose, insulin, and lactic acid metabolism during normal and oxytocin-induced labor for postmaturity.

This investigation was performed to study the metabolism of the major body fuels (viz. glucose and free fatty acids), insulin, and lactic acid during the stress of human labor. In addition, the role of the normal placenta in the transport of these substances between mother and the fetus was evaluated by measuring them in the mother and cord blood at delivery. To study possible alterations of this role in the placenta which had exceeded the normal period of gestation, a second comparable group of women had labor induced with oxytocin 16-18 days beyond the expected date of delivery. A dramatic twofold increase in maternal plasma free fatty acids was observed during labor. There was a lesser but definite increase in blood glucose concentrations. No rise in serum insulin levels was noted which coincided with the changes in blood glucose. Lactic acid concentrations during the course of labor were variable from baseline but at delivery, the concentrations rose to very significant levels. Free fatty acids and blood glucose levels were significantly higher in the maternal than in the fetal side. A significantly positive correlation was noted between the maternal and cord blood values except for free fatty acids in the postmature group. No significant difference, nor a correlation was found between the two compartments in the insulin nor lactic acid levels. These results suggest that during human labor free fatty acids are the principal metabolic fuel. This increase in maternal free fatty acids may serve to spare glucose as a metabolic fuel in the fetus. The mechanism responsible for the increase maternal free fatty acid mobilization remains to be determined. It is not possible to discern any consistant alteration in placental function as a consequence of prolonged gestation.