Appendix LDetailed Evaluation of Vaginal Birth After Cesarean Rates

Publication Details

Introduction

A brief description on the vaginal birth after cesarean (VBAC) rate is included in the text of the evidence report. Detailed descriptions of the studies and analyses conducted on this topic are included in this appendix.

Vaginal Birth After Cesarean

Sixty-seven studies, 14 fair quality prospective cohort studies1–14 and 53 retrospective cohort studies15–67 provided an overall summary estimate for VBAC of 74 percent (95 percent CI: 72 to 75 percent). The heterogeneity of this meta-analysis of 67 observational studies that included 368,304 women was high, I2 greater than 98 percent. To examine this heterogeneity, these studies were stratified and analyzed by study design (prospective versus retrospective; true cohort that included trial of labor (TOL) and elective repeat cesarean delivery (ERCD) versus studies of TOL only), country (United States [U.S.] versus non-U.S.), gestational age ([GA] term only versus all GAs) and by years when the data were collected (completed before 1996, during 1996, and started after 1996). None of these factors were found to result in statistically significant differences analysis of study design yielded a statistically significant association (p<0.05). The summary estimate for VBAC for 14 prospective studies was 73 percent (95 percent CI: 71 to 74 percent) compared with 77 percent (95 percent CI: 75 to 79 percent) for the 53 retrospective studies. The VBAC rate did not differ between studies that included both TOL and ERCD groups and those that focused exclusively on TOL (73 percent; 95 percent CI: 71 to 75 percent versus 74 percent; 95 percent CI 71 to 77 percent).Similarly when studies were stratified by country (U.S. versus Non-U.S.) and by GA at enrollment (term versus non-term studies), no clear associations emerged (Figures L-1 and L-2). The summary estimates for rates of VBAC were similar: for the 43 studies conducted in the U.S., 74 percent (95 percent CI: 72 to 76 percent) versus 73 percent (95 percent CI: 71 to 74 percent) for the 24 studies conducted outside the U.S.. In examining the GA for enrolled patients, the summary estimates for rates of VBAC were again similar: for the 18 studies of term deliveries, 73 percent (95 percent CI: 71 to 75 percent) versus 74 percent (95 percent CI: 72 to 76 percent) for the 49 studies that included preterm and term deliveries.

Figure L-1. Vaginal birth after cesarean rates in United States studies.

Figure L-1

Vaginal birth after cesarean rates in United States studies.

Figure L-2. Vaginal birth after cesarean rates in studies conducted outside the United States.

Figure L-2

Vaginal birth after cesarean rates in studies conducted outside the United States.

Finally, when the studies were stratified by years of data collection, the summary estimates of VBAC again remained similar: 73 percent (95 percent CI: 70 to 77 percent) for the 31 studies completed before 1996;1, 2, 5, 8–14, 16, 26, 27, 30, 36–38, 43, 47–50, 53–55, 59, 61, 63, 65, 67, 68 ; 74 percent (95 percent CI: 72 to 76 percent) for the 19 studies that included data collection during 19963, 19, 22–25, 32–34, 42, 44–46, 52, 57, 58, 60, 62, 64 and 73 percent (95 percent CI: 70 to 75 percent) for the 17 studies started after 1996.4, 6, 7, 15, 17, 18, 20, 21, 28, 29, 31, 35, 39, 41, 51, 56, 66

Summary of vaginal Birth After Cesarean Rate

The rates of VBAC are highly variable in these studies. Most evidence of VBAC rates are from studies based in large tertiary care centers. While TOL rates have dropped over time, VBAC rates reported in observational studies have remained constant for the women who have a TOL. In studies based in the U.S., 74 percent of women who had a TOL delivered vaginally.

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