To the Editor.
—The article by Dr Parrish and colleagues1 stimulated us to reanalyze national primary cesarean rates. Parrish et al found that demographic changes (maternal age, parity, birth weight, and plurality) in the childbearing population from 1970 through 1990 accounted for a quarter of the rise in primary cesarean rates in Washington State. We replicated their analysis using national data for 1971 through 1991 (national data on plurality was not available for 1970) and found that changes in maternal age, parity, birth weight, and plurality considered simultaneously accounted for 21% of the rise in the national primary cesarean rate over this 20-year period (from 4.4% in 1971 to 15.9% in 1991) (the 1971 rate is based on unpublished data from the 1971 National Hospital Discharge Survey conducted by the National Center for Health Statistics; the 1991 rate is based on birth certificate data from the national vital registration
Taffel SM, Clarke SC, Placek PJ. Factors Influencing Primary Cesarean Rates. JAMA. 1994;271(23):1829. doi:10.1001/jama.1994.03510470033026