Low birth weight (LBW) is associated with handicaps, the most prevelant of which affect the brain or its sensory attributes and have a life long impact. We have therefore been interested in nutrition and fetal growth and have studied the relationship between maternal diet and the outcome of pregnancy.

Essential fatty acids are methylene-interrupted, polyenoic fatty acids that are required for cell membrane structure, integrity and function. Some 60% of the structural material of the brain and nervous system is lipid and it uses 20- and 22-carbon-chain-length polyenoic acids specifically in sites of signal transduction and high activity (Fig. 1).

We have been interested in the acquisition of these fatty acids during fetal growth and along with deficits of several nutrients found low intakes of essential fatty acids (EFA) in the mothers of LBW babies. In order to test this food intake data we have analysed the lipids of the umbilical artery as representative of fetal tissue.

We found surprisingly high proportions of the n − 9 eicosatrienoic acid (20:3, n − 9) and docosatrienoic acid (22:3, n − 9). The 20:3, n − 9 is known as the Mead acid and is recognized as a biochemical index of EFA deficiency [1,2]. The 20:3, n − 9/2:4, n − 6 ratio has been used as a biochemical test of general EFA deficiency and the 22:5, n − 6/ 22:4, n − 6 ratio as a marker of docosahexaenoic or n − 3 deficiency. Both ratios were unusually high. Further analysis of 14 babies of different birth weights produced highly significant Pearson correlation coefficients between birth weights and head circumferences, and these two indices, which were negative, and greater in the ethanolamine phosphoglycerides than in the choline phosphoglycerides of the umbilical artery.

The ethanolamine phosphoglycerides are inner membrane lipids and therefore the presence of the Mead acid and high levels of 22:5, n − 6 are statements about the biochemical history of the individual fetus. These indices may therefore have a diagnostic value as a measure of the nutritional status of the fetus during its growth. Because they describe the status of fatty acids specifically used for neural tissue growth, this diagnostic tool has a potential, which needs now to be tested, for assessing risk of neural deficits or damage in, for example, LBW and premature infants.

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