The change in the rate of vaginal birth after caesarean section.

The objective of this study was to determine whether, and to what degree, the change in the vaginal birth after caesarean section (VBAC) rate is due to a change in the characteristics of the obstetric population, the undertaking of a trial of labour (TOL), or the tendency to abandon a TOL once it has been initiated. All women with one prior low transverse caesarean section (CS) and a vertex singleton gestation at term were identified in a registry of CS deliveries occurring at eight academic centres during a 4-year period (1999-2002). Women were classified by their predicted chance of VBAC and year-to-year differences were analysed. Of the 9643 women who met criteria for analysis, 5334 (55.3%) underwent a TOL. From 1999 to 2002, the VBAC rate underwent a steady decline: 51.8% to 45.1% to 37.4% to 29.8% (P < 0.001). Although there were some changes in the characteristics of the population that predispose to successful VBAC, as well as some reduction in the chance that a VBAC is successful once a TOL is undertaken, the most pervasive reason for this decline was that women became increasingly likely to forego a TOL, regardless of their likelihood of vaginal delivery. Based on these results, it appears that the change over time in the VBAC rate is multifactorial, although the greatest change has been a decrease in the frequency with which women undertake a TOL, and this change is observed in all categories of the chance of a successful TOL.