Maternal Phenylketonuria: Consequences of Dietary Non-Adherence and Gaps in Preconception Care—A Case Report

Background: Maternal phenylketonuria (PKU), a metabolic disorder caused by defective phenylalanine hydroxylase activity, requires strict lifelong dietary management to prevent toxic phenylalanine accumulation. During pregnancy, non-adherence to a low-phenylalanine diet can lead to maternal PKU syndrome, resulting in severe neonatal complications, including microcephaly, congenital heart defects, and growth restrictions. Despite advances in metabolic management and preconception care guidelines, adherence remains a significant challenge, particularly among adults transitioning out of pediatric care. This case report examines the clinical consequences of dietary non-adherence in maternal PKU, highlighting the importance of preconception education, metabolic monitoring, and multidisciplinary care in preventing adverse neonatal outcomes. Methods: Using the CARE guidelines, we present the clinical course of a male neonate born to a mother with untreated PKU. Results: The analysis incorporates maternal dietary history, prenatal care details, and neonatal outcomes. Additionally, a review of current literature on maternal PKU management and outcomes contextualizes the findings. The neonate, delivered at 38 weeks via cesarean section, exhibited low birth weight (2150 g), severe microcephaly (head circumference: 28 cm), microphthalmia, and septal heart defects. Maternal dietary non-adherence, beginning in late adolescence, contributed to significantly elevated phenylalanine levels during pregnancy (>20 mg/dL). Prenatal care was initiated in the 23rd week of gestation, delaying dietary intervention. The mother reported limited understanding of the teratogenic risks associated with poor dietary control, which was compounded by gaps in preconception counseling and care continuity. Conclusions: This case underscores the critical need for comprehensive preconception education and lifelong metabolic management for women with PKU. Early and sustained dietary adherence is essential to mitigate neonatal risks. Public health initiatives should prioritize access to preconception care, enhance patient education, and establish robust multidisciplinary support systems to optimize maternal and neonatal outcomes. Addressing barriers such as delayed care initiation and limited dietary support can significantly reduce the burden of maternal PKU syndrome.