Human fetal blood was obtained by cordocentesis from 38 second & third trimester high-risk fetuses. For 31 of these gestations, simultaneously-obtained maternal blood was also available. 14 of the 38 (11 of the 31) gestations resulted in IUGR infants. All samples were assayed for plasma amino acids (AAs), i.e., thr, ser, pro, gly, ala, cit, val, met, ileu, leu, tyr, phe, orn, lys, his, and arg. For both fetal and maternal samples, plasma AAs of the IUGR group did not differ from normal. Fetal plasma levels were significantly higher than maternal levels for at least 6 AAs: thr, val, met, tyr, phe, and lys; these are apparently concentrated in the fetal circulation by the placenta. For 20 normal fetal/maternal plasma pairings, the mean ratio of fetal to maternal AA levels ranged from 1.2 to 2.4 for the 6 AAs. Of 11 IUGR fetal/maternal ratios, 8 fell within the normal range, but 3 were between 0.99 and 1.02; these IUGR gestations exhibited impaired ability to concentrate these 6 AAs in the fetal circulation. These findings 1.) Establish for the first time standard levels for fetal plasma AAs in utero; 2.) Require confirmation and correlation with gestational age as more results accrue; and 3.) Suggest that a portion of IUGR gestations exhibit a defect in the ability to concentrate nutrients within the fetus. These data provide a basis for future diagnostic and, perhaps, therapeutic investigations into gestations at risk for IUGR.
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