Operative vaginal delivery: A comparison of forceps and vacuum for success rate and risk of rectal sphincter injury

Objective: We investigated the success rate of operative vaginal delivery and risk of rectal sphincter injury when forceps or vacuum was used. Study design: Cases were identified by a retrospective review of delivery logbooks and an obstetric database. Rotations were excluded. Failure was defined as inability to deliver the fetus with the initial instrument. Rectal injury was defined as third- or fourth-degree laceration. Institutional review board approval was obtained. P-value of less than .05 was considered significant, and odds ratios (OR) were calculated when appropriate. Results: Data were obtained for 1802 deliveries: 1438 occiput anterior and 364 occiput posterior positions. For occiput anterior position, rectal sphincter injury with forceps was 53.8% and vacuum 26.6% (P <.0001, OR 3.25). Failure rate with vacuum was 6.3% and forceps 0.9% (P <.0001, OR 7.53). For occiput posterior position, rectal injury with forceps was 71.6% and vacuum 33.1% (P <.0001; OR 5.25). Failure rate with vacuum was 33.0% and with forceps 13.6% (P <.0001, OR 3.15). For occiput posterior position, failure rate at mid position with vacuum was 71.4%, and forceps 16.7% (P <.001, OR 12.5). Failure rate at low position with vacuum was 30.8%, and forceps 12.5% (P <.001, OR 3.14). Failure rate with vacuum at mid position was higher than at low position (P <.0001, OR 5.57). Failure rate with forceps at mid and low positions was not significantly different. There was no difference in failure rate between vacuum and forceps at the Outlet position. Conclusion: For both occiput anterior and posterior cases, the use of forceps was associated with a higher success rate than the vacuum, but with greater risk of rectal sphincter injury. The use of either vacuum or forceps from the occiput posterior position was associated with a higher likelihood of rectal injury and lower likelihood of vaginal delivery when compared with the occiput anterior position. (C) 2004 Elsevier Inc. All rights reserved.