ABSTRACT. Plasma cholesterol ester and triglyceride fatty acid compositions of 38 singleton deliveries (23-42 wk), three twins (32, 39, and 40 wk), and their mothers were investigated. No gestational age-dependent changes occurred in maternal fatty acid compositions. Long-chain polyunsaturated fatty acids in fetal cholesterol esters and triglycerides were higher, and their precursors (18:2c,w6 and 18:3c,w3) were lower than those in corresponding maternal lipid classes. Except for 22:6c,w3, 20:2c,w6, and 22:5c,w6, all long-chain polyunsaturated fatty acids in fetal triglycerides increased with advancing gestation. Fetal triglyceride 22:6c,w3/22:5c,w3 ratio decreased, whereas 22:5c,w6/22:4c,w6 remained constant. Fetal cholesterol ester and triglyceride 20:3c,w9 contents were higher than those of corresponding maternal fractions and did not change with gestation. Triglyceride 18:2c,w6 contents of babies with gestational ages of more than 34 wk were linearly related to those of their mothers. The data suggest that increasing triglyceride long-chain polyunsaturated fatty acid content with advancing gestation is partially caused by a6-and a5-desaturase maturation in the liver. 22:6c,w3 and 22:5c,w6/22:4c,w6 and decrease of 22:6c,w3/22:5c,w3 in triglycerides may point to low hepatic a4-desaturation. Transplacental transport of 20:3c,w9, followed by fetal conservation, should be considered. High 18:2c,w6 and low 18:3c,w3 intakes by the mother may unfavorably influence fetal production of 22:6c,w3 in the liver. Because of low hepatic a4-desaturation capacity the influence may be small, however. iPediatr Res 35: 461-469, 1994) Abbreviations CE, cholesterol ester TG, triglyceride FA, fatty acid LCPUFA, long-chain polyunsaturated fatty acid EF A, essential fatty acid LCAT, lecithin:cholesterol acyltransferase PC, phosphatidylcholine AFP, a-fetoprotein Constancy ofThe parent EFA, linoleic (18:2c,w6) and a-linolenic (18:3c,w3) acids, are partially converted into LCPUFA with 20 carbon atoms or more. LCPUFA biosynthetic routes comprise altema-

We studied malabsorption of fat in neonates who were fed either a lard-modified formula (n = 22, gestational age, 33.6 +/- 3.9 wk) or an unmodified formula (n = 14, gestational age, 34.1 +/- 3.7 wk). In both groups fecal lipid consisted almost completely (greater than 90%) of free fatty acids, whose composition was highly correlated with the corresponding formula's fatty acid composition [r = 0.96 (lard modified) and r = 0.99 (standard)]. Both groups had similar relative amounts and compositions of fecal cholesterol esters and triglycerides. Plasma and, to a lesser extent, erythrocyte membrane long-chain-fatty-acid compositions correlated with those of the corresponding formulas. We suggest that the extensive intestinal hydrolysis and limited absorption of dietary lipids is, at least partly, due to lipolysis in the colon. Appearance of triglycerides in the colon may be due to a rapid small-intestinal passage in relation to small-intestinal lipolysis.