ACOG Committee Opinion No. 449: Maternal phenylketonuria.

Phenylketonuria (PKU) is an autosomal recessive disorder of phenylalanine (Phe) metabolism characterized by a deficiency of the hepatic enzyme, phenylalanine hydroxylase, an enzyme responsible for the conversion of phenylalanine to tyrosine, and elevated levels of Phe and Phe metabolite. All women with PKU or hyperphenylalaninemia should be strongly encouraged to receive family planning and preconception counseling. Women with PKU or hyperphenylalaninemia should begin appropriate, medically directed dietary phenylalanine restriction before conception.