摘要：Objectives. We examined factors contributing to shifts in primary cesarean rates in the United States between 1991 and 2002. Methods. US national birth certificate data were used to assess changes in primary cesarean rates stratified according to maternal age, parity, and race/ethnicity. Trends in the occurrence of medical risk factors or complications of labor or delivery listed on birth certificates and the corresponding primary cesarean rates for such conditions were examined. Results. More than half (53%) of the recent increase in overall cesarean rates resulted from rising primary cesarean rates. There was a steady decrease in the primary cesarean rate from 1991 to 1996, followed by a rapid increase from 1996 to 2002. In 2002, more than one fourth of first-time mothers delivered their infants via cesarean. Changing primary cesarean rates were not related to general shifts in mothers’ medical risk profiles. However, rates for virtually every condition listed on birth certificates shifted in the same pattern as with the overall rates. Conclusions . Our results showed that shifts in primary cesarean rates during the study period were not related to shifts in maternal risk profiles. A long-term rise in cesarean rates in the United States began in the mid-1960s and continued to the late 1980s, drawing national attention starting in the late 1970s that focused on reducing the number of cesarean births. 1 The American College of Obstetricians and Gynecologists (ACOG) directed particular attention toward increasing the number of vaginal births after cesarean (VBACs) and issued guidelines in 1988 and 1991 that contributed to the heightened use of VBACs, 2 after which the overall cesarean birth rate steadily decreased until 1996. 3 Notably, the US rate was declining at the same time that national rates in most other industrialized countries were increasing. 4 Largely not noted was that whereas VBAC rates rose to an all-time high in 1996, rates of primary cesareans (i.e., cesarean deliveries among women with no previous such deliveries) declined in a comparable, but inverse, pattern. 3 As VBAC rates peaked, a debate developed in the clinical literature over the safety of VBACs, 5 – 8 and in the late 1990s rates began a rapid decline, with the most recent figures documenting the lowest rate (10.6%) since cesarean deliveries began to be reported on birth certificates in 1989. By 2004, the overall cesarean rate had risen to 29.1% and the primary cesarean rate to 20.6%, both representing the highest national rates ever reported. 9 This latest trend in the overall rate has been noted in government reports, 3 provider group studies, 10 and the popular press, 11 and the majority of attention has been focused on shifting VBAC rates 12 and “patient-choice cesareans” 13 , 14 rather than on changes in primary cesarean rates. We used national birth certificate data to examine changes in primary cesarean rates in the United States between 1991 and 2002. In particular, we assessed demographic and medical risk factors associated with cesarean deliveries in an attempt to determine the degree to which variations in cesarean rates corresponded to changes in the risk profiles of mothers or appeared to be a function of changes in clinical practice.
