Arachidonic and docosahexaenoic acids are strongly associated in maternal and neonatal blood

Background: The red cell membrane fatty acid composition has frequently been used as an index of essential fatty acid (EFA) nutrition. After birth there is a decline in plasma arachidonic acid (AA) and docosahexaenoic (DHA) acids in babies fed on conventional formula which contains only the parent linoleic and α-linolenic acids. In human studies, the red cell phosphoglyceride composition appears to be more constant than that of plasma. In infants fed fish oil without AA, the AA proportions fall in the plasma but much less so in the red cells. This result might be considered to mean that there is no need for preformed AA. On the other hand, in a study where the levels of AA fell there was reduction of infant growth. Indeed, where cell membrane composition does change there is often an associated alteration in physiological functions of membranes. We therefore felt it worth investigating the balance between AA and DHA in a physiological situation where plasma levels are known to change, namely in pregnancy.