Chronic maternal smoking and cord blood amino acid and enzyme levels at term

Objective: To assess the influence of chronic active maternal smoking on cord blood amino acid and enzyme levels at term. Methods: The concentrations of 24 free amino acids, total protein, and five enzymes were measured in samples of maternal and fetal cord venous plasma from 24 nonsmokers who were not exposed to tobacco smoke and 24 chronic smokers. Cotinine levels were also measured in maternal plasma to evaluate fetal tobacco exposure. The pregnancies were between 37 and 40 weeks' gestation, were uncomplicated, and were delivered vaginally. Results: Fetal weight was significantly (P < .01) lower in the smokers than in controls. A positive significant (P < .001) correlation was found between maternal and umbilical venous cotinine concentrations. Significantly lower concentrations of aspartic acid (P < .01), hydroxyproline (P < .05), threonine (P < .005), alanine (P < .05), alpha -aminobutyric acid (P < .001), methionine (P < .05), tyrosine (P < .001), phenylalanine (P < .01), and lysine (P < .05) were found in the venous cord plasma of the smokers compared with nonsmokers. The fetomaternal ratios were similar in both groups. The umbilical plasma alkaline phosphatase activity was significantly (P < .01) lower in the smokers than in the controls. Conclusion: Chronic maternal smoking is associated with alterations of protein metabolism and enzyme activity in fetal cord blood. These may be secondary to irreversible changes in the cellular functions of the trophoblast and may contribute to fetal growth restriction. (Obstet Gynecol 2001; 97:57-61. (C) 2001 by The American College of Obstetricians and Gynecologists.)