Risk adjustment in maternity care: the use of indirect standardization

Annual US national rates of family physicians providing maternity care are decreasing and rates of cesarean delivery are increasing. Family physicians tend to have lower cesarean delivery rates than obstetrician specialists, but this association is usually explained by an assumed lower pre-delivery risk for cesarean delivery. This study was developed to compare the estimated risk of cesarean delivery in patients of the two specialties. A retrospective cohort study within an urban teaching hospital compared 100 family- physician treated subjects to 300 subjects treated by obstetrician-specialists. Risk factors for cesarean delivery were identified, and an indirect standardization procedure was used to compare the pre-38 week of gestation risk of cesarean delivery in the two groups. The patients treated by family physicians had a projected pre-38 week of gestation risk of cesarean delivery (17.4%) that was similar to the actual rate of cesarean delivery in the obstetrician-specialist group (16.7%). The Standardized Cesarean Delivery Ratio was 1.04. Lower cesarean delivery rates provided by family physicians may not be simply due to case-mix issues. Additional studies comparing the pre-delivery estimation of cesarean delivery risk would be helpful in measuring the relative levels of obstetric risk of patients treated by different maternity-care provider types.