Levels of free fatty acids and arachidonic acid in pregnancy and labor.

Serum levels of total FA and nonesterified AA were measured during 10 normal pregnancies, subsequent labors, and postpartum periods and in cord blood. The proportion of AA present in PL, CE, and TGs was also measured. A general rise of total FA was noted as the pregnancy progressed, followed by a marked elevation in total FA during labor. By 2 days postpartum, the FA levels had dropped to their lowest values. Cord blood levels were generally much lower than any maternal levels. Mean serum free AA levels were elevated in the second trimester and again during labor, and the percentage of AA in the total FAs was uniformly lower during labor than at any time during pregnancy. The percentage of total FAs made up by AA was much higher in cord blood than in maternal blood. The esterified fatty acid fractions in cord blood were also much richer in AA than those in maternal blood. The possibility that AA circulating in the bloodstream may play a part in the propagation of labor is suggested.