Quality of care after a horizontal merger between two large academic hospitals.

Background: Hospital mergers remain common, but their influence on healthcare quality varies. Data on effects of European hospital mergers are ill defined, and academic hospitals in particular. This case study assesses early quality of care changes in two formerly competing Dutch academic hospitals that merged on June 6, 2018. Methods: Statistical process control and interrupted time series analysis were performed. All adult, non-psychiatric patients, admitted between 01-03-2016 and 01-10-2022 were eligible for analysis. Primary outcome measure was all cause in-hospital mortality (or hospice), secondary outcomes were unplanned 30-day readmissions to same hospital, length of stay, and patients' hospital rating. Data were obtained from electronic health records, and patient experience surveys. Findings: The mean (SD) age of the 573 813 included patients was 54·3 (18·9) years. The minority was female (277 817, 48·4 %), and most admissions were acute (308 597, 53·8 %). No merger related change in mortality was found in the first 20 months post-merger (limited to the pre-Covid-19 era). For this same period, the 30-day readmission incidence changed to a downward slope post-merger, and the length of stay shortened (immediate level-change -3·796 % (95 % CI, -5·776 % to -1·816 %) and trend-change -0·150 % per month (95 % CI, -0·307 % to 0·007 %)). Patients' hospital ratings seemed to improve post-merger. Interpretation: In this quality improvement study, a full- and gradual post-merger integration strategy for a Dutch academic hospital merger was not associated with changes in in-hospital mortality, and yielded slight improved results for secondary quality of care outcomes.