High maternal blood PHE during pregnancy results in microcephaly, low birth weight, congenital heart disease, and intellectual disability in offspring of women with PKU. There is a wealth of evidence to show that this Maternal PKU syndrome (MPKUS) can be prevented if maternal blood PHE is controlled within a treatment range of 120-360 µmol/L before and during pregnancy. However very few studies contain robust dietary intake data. The primary source of nutrient intake data is the Maternal PKU Collaborative Study (MPKUCS), which indicated that protein, energy, fat, and vitamin B₁₂ intakes all impacted blood PHE and/or birth outcomes. The diet for women with PKU who are pregnant must provide adequate protein, energy, fat, vitamins, and minerals to support normal fetal growth and development. This necessitates the use of low or PHE-free medical foods, and often modified low protein foods. The diet is very restrictive and unpalatable and adherence is often suboptimal, especially in women who have severe forms of PKU, less education, and lower IQ and socioeconomic status. However, with close monitoring of blood PHE and biochemical markers of protein, vitamin, and mineral status, normal birth outcomes are possible. Women with PKU are encouraged to maintain dietary therapy after pregnancy and to breastfeed their infants. Pyshosocial support during pregnancy is recommended. Sapropterin use in pregnancy has been limited and does not appear to be teratogenic, and is most likely to be of benefit to women with less severe forms of PKU. Large neutral amino acid therapy alone is not recommended during pregnancy.