Enhancing the Classification of Congenital Heart Defects for Outcome Association Studies in Birth Defects Registries

Abstract

Introduction: Traditional strategies for grouping congenital heart defects (CHDs) using birth defect registry data do not adequately address differences in expected clinical consequences between different combinations of CHDs. We report a lesion-specific classification system for birth defect registry-based outcome studies.

Methods: For Core Cardiac Lesion Outcome Classifications (C-CLOC) groups, common CHDs expected to have reasonable clinical homogeneity were defined. Criteria based on combinations of Centers for Disease and Control-modified British Pediatric Association (BPA) codes were defined for each C-CLOC group. To demonstrate proof of concept and retention of reasonable case counts within C-CLOC groups, Texas Birth Defect Registry data (1999-2017 deliveries) were used to compare case counts and neonatal mortality between traditional vs. C-CLOC classification approaches.

Results: C-CLOC defined 59 CHD groups among 62,262 infants with CHDs. Classifying cases into the single, mutually exclusive C-CLOC group reflecting the highest complexity CHD present reduced case counts among lower complexity lesions (e.g., 86.5% of cases with a common atrium BPA code were reclassified to a higher complexity group for a co-occurring CHD). As expected, C-CLOC groups had retained larger sample sizes (i.e., representing presumably better-powered analytic groups) compared to cases with only one CHD code and no occurring CHDs.

Discussion: This new CHD classification system for investigators using birth defect registry data, C-CLOC, is expected to balance clinical outcome homogeneity in analytic groups while maintaining sufficiently large case counts within categories, thus improving power for CHD-specific outcome association comparisons. Future outcome studies utilizing C-CLOC-based classifications are planned.

Keywords: birth defect registry; classification; congenital anomalies; congenital heart defects; surveillance programs.

Figure 1.. Summarization of 59 Parent Groups, Main Groups, and Subgroups Evaluated Using the C-CLOC Approach

Figure 2.. Sample Size and Percent Neonatal Mortality by Congenital Heart Defect and Approach

ASD: Atrial septal defect; CHD: Congenital heart defect; C-CLOC: Core Cardiac Lesion Outcome Classifications; dTGA:Dextro-transposition of the great arteries; HLHS: Hypoplastic left heart syndrome; PAPVR: Partial anomalous pulmonary venous return; PV: Pulmonary valve; TBDR: Texas Birth Defect Registry; TOF: Tetralogy of Fallot. Defects with ≤5 neonatal deaths or defects in which >90% of cases with a given CHD code were excluded on the exclusive approach (resulting in statistically unreliable estimates due to low sample sizes) ascertained in each approach were not included. Parent CHD groups are delineated in red text on the x-axis.