Are we making a real difference? Update on 'hidden mortality' in the management of congenital diaphragmatic hernia

Reports of improved survival rates for cases of congenital diaphragmatic hernia (CDH) patients have prevailed in the literature over the past 10 years. These improvements have been attributed to advances in medical management in the postnatal period. However, further inquiries into the true survival of CDH patients through population-based studies have revealed that the reported increase in survival outcomes, which are often single institution-based reports, are confounded by case selection bias which fails to consider those CDH patients who do not reach the referral centers. This apparent discrepancy between population-based and institution-based statistics raises the question of 'hidden mortality' and the role it plays in both research and clinical medicine. In this review we will examine the reported survival outcomes of CDH from both institution- and population-based perspectives and explore the presence and implications of hidden mortality on research methodology and clinical practice.