The international study of pregnancy outcome in women with maternal phenylketonuria: report of a 12-year study.

Objective: The purpose of this report was to update the results of the Maternal Phenylketonuria Collaborative Study, which was established to assess the efficacy of a phenylalanine-restricted diet in preventing morbidity among the offspring of women with hyperphenylalaninemia.

Study Design: During a 12-year period 576 women with hyperphenylalaninemia were enrolled in this study. Outcome measures were stratified according to classification of maternal hyperphenylalaninemia and the time at which dietary control of phenylalanine level was achieved.

Results: Optimal physical and cognitive fetal outcomes occurred when maternal blood phenylalanine level <600 micromol/L was achieved by 8 to 10 weeks' gestation and maintained throughout pregnancy (trimester average,
Conclusions: The achievement of blood phenylalanine level control through a phenylalanine-restricted diet significantly diminished the occurrence of congenital abnormalities among offspring of women with hyperphenylalaninemia and improved early intellectual progress of these offspring.