Sensitivity of spontaneous abortion classification to hierarchical algorithm assumptions in US commercial claims data, 2018–2024

Background: Identifying spontaneous abortion (SAB) and induced abortion (IAB) in administrative data compared to other pregnancy outcomes is challenging due to shared billing codes and lack of reimbursement by many insurers. Methods: We performed a retrospective cohort study using the Merative MarketScan Commercial Database from 2018–2024. We adapted a previously published hierarchical algorithm to reduce the number of unknown or ambiguous pregnancy outcomes. We then tested the assumptions of the hierarchy by alternating the order of the diagnosis, procedural, and diagnosis-related group (DRG) codes within the algorithm for SAB and IAB. Results: Our dataset included 2,418,986 pregnancy episodes. Our modified algorithm improved the sensitivity for SAB, identifying a 17.5% incidence compared to 14.9% for previously published algorithms and reduced unclassified outcomes from 17.4% to 13.4%. Prioritizing IAB in the algorithm hierarchy over SAB identified an additional 8,623 IAB cases. However, IAB identification remained low at less than 5% of pregnancy episodes. Conclusions: Following the Dobbs decision, it is critical that researchers accurately identify early pregnancy claims and remain transparent in their methodology. Our algorithm improved sensitivity for SAB and reduced unknown outcomes. However, claims-based analyses may systematically undercount IAB, with implications for research-informed reproductive health policy.