OBJECTIVE—Neonates of women with gestational diabetes mellitus (GDM) have reduced levels of arachidonic acid (AA) (20:4 n-6) and docosahexaenoic acid (DHA) (22:6 n-3). To assess whether this is the result of impaired placental transfer or endogenous fetal metabolism, fatty acids in umbilical venous and arterial plasma were analyzed in neonates of GDM women. RESEARCH DESIGN AND METHODS—Fatty acids were analyzed by gas chromatography in the plasma of 15 subjects with GDM and 30 healthy control subjects undergoing elective cesarean section and in vein and artery cord blood collected separately. RESULTS—The percentages of AA (20:4 n-6), DHA (22:6 n-3), and total n-6 or n-3 polyunsaturated fatty acids (PUFAs) as well as total PUFAs were lower in umbilical arterial but not in venous plasma of neonates of the GDM versus the control group. CONCLUSIONS—An altered handling or metabolism of long-chain PUFAs by the fetus rather than impaired placental transfer seems to be responsible for the lower proportion of those fatty acids in the plasma of neonates of GDM mothers.