Prenatal diagnosis mediates the relationship between disease complexity and intervention timing for congenital heart defects.

Introduction: Previous studies comparing timing of postnatal intervention among patients with prenatal versus postnatal diagnosis of a congenital heart defect (CHD) have yielded conflicting results due to challenges in controlling for CHD complexity. The objective of this analysis is to take an alternative approach: to determine whether prenatal diagnosis mediates, or explains, the relationship between CHD complexity and age at intervention. Methods: A retrospective cohort study including infants who received intervention for CHD at < 60 days of life, 2015-2021, at a high-volume CHD surgical center. The exposure was CHD complexity (low, moderate, and high). The mediator was prenatal diagnosis (yes, no). The outcome was age at intervention (cardiac surgery or interventional catheterization, whichever came first) in days. Covariates included sociodemographic and clinical characteristics of the pregnant individual and infant. Mediation analysis used linear probability regressions with a COVID-19-era fixed effect and robust standard errors. Results: Of 429 infants, 28% had high-, 63% had moderate-, and 8% had low-complexity CHD; 68% had a prenatal diagnosis. The median age at intervention was 6 (IQR 4-14) days. In adjusted models, prenatal diagnosis mediated 27%-29% of the association between CHD complexity and age at intervention (indirect effects: moderate complexity vs. low complexity: 3.7, 95%CI 1.4-6.1 days; high complexity vs. low complexity: 5.5, 95%CI 2.2-8.8 days). Conclusion: Complex CHDs are intervened upon earlier, partly because they are likelier to be prenatally detected, than low-complexity defects. Prenatal diagnosis plays a mechanistic role in improving access to care for infants with complex CHD.