a condition in women who have phenylketonuria (PKU) and become pregnant. Expectant mothers with high levels of blood phenylalanine—hyperphenylalaninemia—are at risk of giving birth to offspring with high rates of congenital heart defects, intrauterine growth retardation, intellectual disability, and microcephaly (a small head). Treatment entails dietary management for the expectant mother before and during pregnancy to reduce blood levels of phenylalanine.