Japan at the limits of viability: national experience and evolving outcomes of infants born at 22-23 weeks' gestation.

Infants born at 22-23 weeks' gestation represent the limits of viability with substantial international variation in outcomes. Japan has consistently reported some of the highest survival rates; however, the underlying healthcare systems and clinical practices have not been comprehensively synthesized. This review summarizes Japan's national experience using data from a nationwide network database, epidemiologic studies, clinical practice surveys, and international comparisons. Survival at discharge is approximately 60% and 80% for infants born at 22 and 23 weeks' gestation, respectively, with relatively low rates of severe intraventricular hemorrhage and necrotizing enterocolitis. Key healthcare system features include regionalized perinatal care promoting antenatal maternal transfer, a nationwide clinical network for benchmarking, and universal health insurance. Clinical practice is characterized by active resuscitation and meticulous, individualized, pathophysiology-based management, including invasive respiratory support, echocardiography-guided hemodynamic management, intensive neuroprotection, and specialized nursing care. The effectiveness of these practices remains uncertain, and further research is needed. Continuous outcome monitoring and quality improvement are essential to refine context-specific strategies. IMPACT: This review provides the comprehensive synthesis of Japan's national experience in the care of infants born at 22-23 weeks' gestation, integrating outcomes with healthcare system structures and clinical practices. It identifies key system-level and clinical factors-such as regionalized perinatal care, nationwide data-driven quality improvement, and pathophysiology-based management-that may contribute to Japan's high survival rates and relatively low morbidity. It highlights the importance of integrated "package-of-care" approaches and continuous outcome monitoring, offering insights that may inform strategies to improve outcomes at the limits of viability globally.