To examine the impact of intrauterine growth retardation (IUGR) on essential fatty acids in human placenta, fatty acid composition in total acylglycerol and in the major phosphoglycerides phosphatidylcholine (PC) and phosphatidylethanolamine (PE), of 15 placentas from small for gestational age (SGA) births was compared with that of 7 control placentas. The acylglycerol fatty acid content was similar between the two groups, but the proportion of fatty acid of the linoleic acid series, including arachidonic acid, was significantly lower in SGA placentas. When the fatty acid composition in PC was studied, the reduction in fatty acids of the linoleic acid was even more striking, and fatty acids of the linolenic acid series were also significantly less in the SGA group. These fatty acid changes in placenta membrane phospholipids can effect the transport of important nutrients to the fetal compartment. The decreased level of arachidonic acid and docosahexanoic acid might also lead to a disturbed formation of fetal thromboxane and prostacyclin. However, cord plasma PC fatty acid patterns were nearly identical in the two groups suggesting that in IUGR, the essential fatty acids will be transported to the fetus at the expense of the placenta. © 1991.