Maternal and infant serum phenylalanine levels and pregnancy outcome in infants of nonphenylketonuric mothers.

Maternal consumption of casein is associated with excess low birthweight and infant mortality. Genetically normal infants of hyperphenylalaninemic mothers also show excess low birthweight and mortality. To determine whether the phenylalanine in casein could produce a secondary phenylketonuria effect, maternal serum phenylalanine levels were measured in 77 specimens of maternal blood serum drawn during the 15th through 21st weeks of pregnancy and in 55 specimens of cord [correction of cold] blood collected from the same mothers' infants. Maternal serum phenylalanine levels correlated negatively with infant birthweight in the 41 infants for whom appropriate confounders were known. Infant serum phenylalanine levels did not correlate with birthweight. Neither maternal nor infant serum phenylalanine levels correlated with 1-minute Apgar scores. A negative association was seen between both maternal and infant serum phenylalanine levels and 5-minute Apgar scores when appropriate confounders were controlled.