ASSESSING THE ROLE OF CASE-MIX IN CESAREAN DELIVERY RATES

Objective: Implicit in comparisons of unadjusted cesarean rates for ho spitals and providers is the assumption that differences result from m anagement practices rather than differences in case mix. This study pr oposes a method for comparison of cesarean rates that takes the effect of case mix into account. Methods: All women delivered of infants at our institution from December 1, 1994, through July 31, 1995, were cla ssified according to whether they received care from community-based p ractitioners (N = 3913) or from the hospital-based practice that serve s a higher-risk population (N = 1556). Women were categorized accordin g to both obstetric history (nulliparas, multiparas without a previous cesarean, multiparas with a previous cesarean) and the presence of ob stetric conditions influencing the risk of cesarean delivery (multiple birth, breech presentation or transverse lie, preterm, no trial of la bor for a medical indication). We determined the percent of women in e ach parity-obstetric condition subgroup and calculated a standardized cesarean rate for the hospital-based practice using the case mix of th e community-based practitioners as the standard. Results: The crude ce sarean rate was higher for the hospital-based practice (24.4%) than fo r the community-based practitioners (21.5%), a rate difference of 2.9% (95% confidence interval = 0.4%, 5.4%; P =.02). However, the proporti on of: women falling into categories conferring a high risk of cesarea n delivery (multiple pregnancy, breech presentation or transverse lie, preterm, no trial of labor permitted) was twice as high for the hospi tal-based practice (24.4% hospital, 12.1% community). The standardizat ion indicates that if the hospital-based practitioners had the same ca se mix as community-based practitioners, their overall cesarean rate w ould be 20.1%, similar to the 21.5% rate of community providers (rate difference = -1.4%, 95% confidence interval -3.1%, 0.3%; P =.11). Conc lusion: Standardization for case mix provides a mechanism for distingu ishing differences in cesarean rates resulting from case mix from thos e relating to differences in practice. The methodology is not complex and could be applied to facilitate fairer comparisons of rates among p roviders and across institutions. (C) 1998 by The American College of Obstetricians and Gynecologists.