The transfer of free fatty acids across the human placenta.

Thirty-three matched maternal venous and umbilical cord vein and artery plasma samples were obtained at elective caesarean section and the concentrations of the individual free fatty acids determined. The maternal levels were 1.009 (SEM 0.043) and the umbilical vein-artery difference was 0.036 (SEM 0.011) mmol/l. There was a significant correlation between the mean concentration in maternal venous blood and the vein-artery difference for myristic, palmitic, stearic, linoleic and docosahexaenoic acids but not for oleic acid. When arachidonic acid concentration in the fetus was high, then the vein-artery difference was negative (flow to the placenta), when it was low, the difference was positive (flow to the fetus). Thus whilst there appears in general to be a flow of fatty acid to the fetus dependent on maternal free fatty acid concentrations, the transfer of arachidonic acid is largely determined by other factors. The reasons why oleic acid does not behave like the other fatty acids is not clear.