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Objective: This study described the prevalence and duration of mothers’ breastfeeding infants with phenylketonuria (PKU) and explored factors related to duration of breastfeeding as a surrogate for breastfeeding success. Subjects and

Methods: Descriptive analysis as performed from an international Internet survey of mothers (n = 103) who met the inclusion criteria: (1) at least 21 years of age, (2) able to read and write in English, (3) child with PKU, and (4) living in the United States or Canada.

Results: Of the 103 mothers, 89 (86%) initiated breastfeeding immediately following delivery, whereas 14 (14%) chose bottle feeding. In comparison to breastfeeding after delivery, significantly fewer mothers breastfed after diagnosis (McNemar’s v2 = 30.33, p < 0.001; n = 72 vs. n = 89). Breastfeeding duration ranged from less than 1 month to 24 months with one modal duration category (n = 20, 22%) at less than 1 month. The timing of the addition of commercial infant formula to supplement breastfeeding or expressed mothers’ milk was associated with a shorter duration of breastfeeding among infants with PKU: v2 (42, n = 73) = 88.13, p < 0.001.

Conclusions: PKU is treated with phenylalanine (Phe) restriction. Breastfeeding infants with PKU is challenging in part because Phe intake is difficult to determine precisely. We studied breastfeeding duration in infants with PKU and factors associated with success. Further research should identify the unique needs of mothers’ breastfeeding infants with PKU to guide the development of interventions specific to these mothers to support their efforts to continue breastfeeding after the diagnosis of PKU.