New England Maternal PKU Project: prospective study of untreated and treated pregnancies and their outcomes.

Four women with classic phenylketonuria (blood phenylalanine greater than 1200 mumol/L) were given a phenylalanine-restricted diet; three also received L-tyrosine supplements. Biochemical measures of nutrition were normal except for iron deficiency anemia, and in one woman folate deficiency. One pregnancy in which treatment began before conception and another treated from 8 weeks gestation, both with blood phenylalanine levels maintained at 120 to 730 mumol/L, resulted in normal newborn infants whose postnatal growth and development have also been normal. A third pregnancy, treated from 6 gestational weeks, was marked by poor dietary compliance until the middle of the second trimester; fetal microcephaly was identified by ultrasonography at 28 weeks but not at 21 weeks. The child has microcephaly and motor delay. The fourth pregnancy, not treated until the third trimester, produced a child with microcephaly, mental retardation, hyperactivity, and neurologic deficits. It is likely that fetal damage from maternal phenylketonuria can be largely and perhaps entirely prevented by dietary therapy, but therapy must begin before conception for the best chance of a normal infant.