Fatty acid composition of erythrocyte phosphatidylcholines was determined by high-resolution capillary gas chromatography in Spanish (n = 120), German (n = 78) and Hungarian (n = 43) expectant women at the 20th week of gestation. The sum of trans isomeric fatty acids was significantly (p < 0.05) lower in Hungarian (0.68 [0.43]% wt/wt, median [IQR]) than in Spanish (0.82 [0.53]) expectant women. There were no significant correlations between the sum of trans isomers and linoleic acid or alpha-linolenic acid in either of the three groups. In contrast, there were significant inverse correlations between the sum of trans fatty acids and arachidonic acid and docosahexaenoic acid in all the three groups. These data raise the possibility that maternal trans isomeric fatty acid status may be inversely associated to the essential fatty acid status of the foetus.