Maternal phenylketonuria collaborative study, obstetric aspects and outcome: The first 6 years

Objective: The purpose of this study was to evaluate the efficacy of a phenylalanine-restricted diet in reducing fetal morbidity associated with maternal hyperphenylalaninemia in women of childbearing age with blood phenylalanine levels >240 μmol/L (>4 mg/dl) on an unrestricted diet. Study Design: Two hundred thirteen pregnant women with hyperphenylalaninemia that resulted in 134 live births have been enrolled in the study. Outcome measures were subject to the χ² test, Fisher exact test, analysis of variance, t test, or Wilcoxon nonparametric test for analysis. Results: Optimal fetal outcome appeared to occur when blood phenylalanine levels <600 μmol/L (<10 mg/dl) were achieved by 8 to 10 weeks' gestation and maintained throughout pregnancy (trimester averages of ≤360 μmol/L (≤6 mg/dl)). Initiation of dietary therapy during the third trimester of pregnancy appears to have little beneficial effect on the fetus. Conclusions: Preconceptual counseling and early entrance into a prenatal care program is essential in achieving optimal fetal outcome in women with hyperphenylalaninemia.