Plasma amino acids of the mid-trimester human fetus.

The amino acid concentrations in umbilical cord plasma taken at fetoscopy were measured from 12 fetuses between 18 and 29 weeks gestation. Concurrent maternal plasma levels were measured. Fetal plasma showed consistently higher concentrations of plasma amino acids with the ratios varying between 1.1:1 and 3:1 and the difference always reached statistical significance. It is suggested that these results reflect the in vivo situation of the mid-trimester human fetus.