Clinical case mix adjustment of cesarean delivery rates in U.S. military hospitals, 2002

OBJECTIVE: To assess whether significant variations in observed cesarean rates in U.S. military hospitals may be attributed to differences in clinical case mix. METHODS: Hospital discharge records for births in U.S. military hospitals in 2002 were grouped into mutually exclusive clinical strata to calculate predicted cesarean rates for subgroups defined by maternal race, health plan, hospital location, delivery volume, teaching status, and neonatal intensive care unit (NICU) status. The 95% confidence interval (CI) around each standardized ratio (SR) of the observed-to-predicted cesarean rate was used to assess statistical significance. RESULTS: Observed cesarean rates were significantly higher than predicted rates for small hospitals (23.1% and 20.4%, respectively, SR 1.13, 95% CI 1.08-1.19), teaching hospitals (23.7% and 22.5%, respectively, SR 1.05, 95% CI 1.02-1.08), black women (25.1% and 22.8%, respectively, SR 1.10, 95% CI 1.05-1.14), and other minorities (22.7%, and 21.6%, respectively, SR 1.05, 95% CI 1.01-1.09). No significant differences between observed and predicted cesarean rates were found across hospital locations or NICU status. Significant differences found for non-managed care beneficiaries were attributed to teaching status of the hospitals in which they delivered. CONCLUSION: Clinical case mix does not adequately account for the relatively high rates of cesarean delivery observed for small hospitals and teaching hospitals and among black women in the study population. Further study is recommended to identify additional clinical and nonclinical factors that should be considered when comparing performance across institutions, health plans, or individual providers.