Maternal concentrations and fetal-maternal concentration differences of plasma amino acids in normal and intrauterine growth restricted pregnancies

OBJECTIVES: Our purpose was to determine whether maternal amino acid concentration changes during gestation in pregnancies with intrauterine growth restriction as in normal pregnancies and to verify whether these changes are related to changes in fetal-maternal differences. STUDY DESIGN: Amino acid concentrations were measured in 5 nonpregnant women, in 11 second- trimester and 10 third-trimester pregnant women with appropriate-for- gestational-age fetuses, and in 23 pregnant women with intrauterine growth restriction. Umbilical venous amino acids were measured at the time of fetal blood sampling. The severity of intrauterine growth restriction was assessed by Doppler velocimetry and fetal heart rate and by evaluation of oxygenation and acid-base balance. RESULTS: In normal pregnant women the maternal concentration of most amino acids was significantly lower in both the second and third trimesters compared with nonpregnant women. In intrauterine growth restriction the maternal concentrations of most essential amino acids were significantly higher than in appropriate-for-gestational-age pregnancies. This observation, coupled with lower fetal amino acid concentrations in intrauterine growth restriction, leads to significantly lower fetal-maternal differences. CONCLUSIONS: Normal pregnant women have a significant decrease in amino acid concentrations compared with nonpregnant women, whereas in intrauterine growth restriction maternal amino acids are reduced less. Significantly lower fetal-maternal concentration differences are present in intrauterine growth restriction, independent of the degree of severity.