The effect of a maternal infusion of amino acids on umbilical uptake in pregnancies complicated by intrauterine growth restriction

Objective: To establish whether, in human pregnancies complicated by intrauterine growth restriction (IUGR), the maternal intravenous infusion of amino acids can increase fetal amino acid concentrations and umbilical uptake. Study Design: Before elective cesarean delivery, a solution of amino acids was infused into a maternal vein in 8 patients with pregnancies complicated by IUGR (experimental group). At cesarean delivery, maternal, umbilical venous, and arterial blood samples were obtained. Ten comparable IUGR pregnancies were compared with those in the experimental group. Results: In the experimental group, all maternal amino acid concentrations were increased significantly. In the umbilical vein, valine, methionine, isoleucine, leucine, phenylalanine, arginine, serine, glycine, and proline concentrations were elevated. Umbilical venoarterial differences of amino acid per mole of oxygen for leucine, isoleucine, methionine, arginine, glycine, serine, and proline were elevated but not for lysine, histidine, threonine, valine, and phenylalanine. Conclusion: In pregnancies complicated by IUGR, increasing the maternal concentration of amino acids leads to an increased umbilical uptake of some of the amino acids to the fetus. There was no evidence of a change in the uptake of 3 essential amino acids: lysine, histidine, and threonine. (Am J Obstet Gynecol 2002;187:741-6.)