Serum amino acid concentrations during pregnancy of women heterozygous for phenylketonuria.

Increased concentrations of phenylalanine were found in blood specimens from pregnant women who were heterozygous for phenylketonuria, but the concentration differences between normal controls, nonpregnant heterozygous, and pregnant heterozygous, and pregnant heterozygous women were small. Phenylalanine concentrations in cord blood were in the same range as in maternal blood at time of delivery. Phenylalanie concentrations in the carrier do not rise sufficiently during pregnancy to harm the infant in utero.