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Context: Untreated maternal phenylketonuria (PKU) increases risk for developmental problems in offspring. The extent to which this risk is reduced by maternal dietary therapy at various stages of pregnancy is not known., Objective: To determine whether dietary treatment during pregnancy of women with PKU affects developmental outcomes of offspring., Design: The Maternal PKU Collaborative Study, an ongoing, longitudinal prospective study begun in 1984., Setting: A total of 78 metabolic clinics and obstetrical offices in the United States, Canada, and Germany., Participants: A total of 253 children of women with PKU (n = 149), with untreated mild hyperphenylalaninemia (n = 33), or without known metabolic problems (comparison group; n = 71) were followed up to age 4 years., Intervention: Women with PKU were offered a low-phenylalanine diet prior to or during pregnancy with the aim of maintaining metabolic control (plasma phenylalanine < or =10 mg/dL [< or =605 micromol/L]). Women with mild hyperphenylalaninemia, who had plasma phenylalanine levels of no more than 10 mg/dL (605 micromol/L) on a normal diet, were not treated., Main Outcome Measures: Children's scores on cognitive and behavioral assessments (McCarthy Scales of Children's Abilities, Test of Language Development, Achenbach Child Behavior Checklist, Vineland Adaptive Behavior Scales, and Home Observation for Measurement of the Environment), compared by maternal metabolic status at 0 to 10 weeks', 10 to 20 weeks', and after 20 weeks' gestation., Results: Scores on the McCarthy General Cognitive Index decreased as weeks to metabolic control increased (r = -0.58; P<.001). Offspring of women who had metabolic control prior to pregnancy had a mean (SD) score of 99 (13). Forty-seven percent of offspring whose mothers did not have metabolic control by 20 weeks' gestation had a General Cognitive Index score 2 SDs below the norm. Overall, 30% of children born to mothers with PKU had social and behavioral problems., Conclusions: Our data suggest that delayed development in offspring of women with PKU is associated with lack of maternal metabolic control prior to or early in pregnancy. Treatment at any time during pregnancy may reduce the severity of delay.

Neonatal screening for phenylketonuria (PKU) has created an unexpected problem as females with PKU are reaching childbearing age. Surveys have revealed that maternal phenylalanine blood concentrations above 1200 mumol/L are associated with microcephaly, mental retardation, congenital heart defects, and intrauterine growth retardation among their offspring. It is estimated that as many as 3000 hyperphenylalaninemic females may be at risk for producing these fetal abnormalities. To examine this problem, the North American Maternal PKU Collaborative Study has been developed to evaluate the efficacy of a phenylalanine-restricted diet in reducing fetal morbidity. Preliminary findings indicate that phenylalanine restriction should begin before conception for females with PKU planning a pregnancy. Dietary control should maintain maternal blood phenylalanine levels between 120 and 360 mumol/L and should provide adequate energy, protein, vitamin, and mineral intake. Pregnant hyperphenylalaninemic females who achieved metabolic control after conception or by the 10th week of pregnancy had a better offspring outcome than anticipated.

One hundred ninety-five infants who met diagnostic criteria for enrollment in the Collaborative Study of Children Treated for Phenylketonuria (PKU) underwent a standard three-day challenge with 180 mg/kg/day of phenylalanine for confirmation of diagnosis. A sustained rise in serum phenylalanine levels of greater than 20 mg/dl was observed in 166 infants (85.1%), compatible with the diagnosis of classical PKU. In the remaining 29 infants (14.9%), the serum phenylalanine concentration either did not reach 20 mg/dL or, having achieved this level, subsequently declined below this point by 72 hours. It was agreed that these 29 patients had variant PKU and they were dropped from the Collaborative Study. We recommend that all infants diagnosed as having classic PKU undergo a challenge to confirm the diagnosis and need for continued treatment.