The Safety of Planned Vaginal Birth After Cesarean
by Henci Goer

Commentary on: Mozurkewich EL and Hutton EK. Elective repeat cesarean delivery versus trial of labor: a meta-analysis of the literature from 1989 to 1999. Am J Obstet Gynecol 2000:183:1187-97. [Abstract]

Study design and results: systematic review and meta-analysis of 11 studies comprising 23,486 planned vaginal births and 16,230 elective repeat cesarean sections. Note: The investigators only report odds ratios. I calculated the “absolute differences.”

• Combined fetal and neonatal mortality rate:
  • planned vaginal birth: 136/23,486 = 5.8 per 1000
  • elective repeat cesarean section: 56/16,239 = 3.4 per 1000
  • odds ratio: 1.71; 95% confidence interval 1.28 to 2.28
  • absolute difference: 2.4 per 1000
• hemorrhage requiring transfusion: (7 studies)
  • planned vaginal birth: 100/8988 = 1.1%
  • elective repeat cesarean section: 94/5450 = 1.7%
  • odds ratio: 0.57; 95% confidence interval 0.42 to 0.76
  • absolute difference: 8 per 1000
• hysterectomy: (6 studies)
  • planned vaginal birth: 43/26,786 = 1.6 per 1000
  • elective repeat cesarean section: 71/17,337 = 4.1 per 1000
  • odds ratio: 0.39; 95% confidence interval 0.27 to 0.57
  • absolute difference: 2.5 per 1000

Problems include but are not limited to the following:

• The investigators included fetal and neonatal deaths unrelated to birth route: The investigators performed a subanalysis excluding deaths before the onset of labor, lethal anomalies, and prematurity, but buried those results in the text and omitted them from the abstract, which is all most people read. If we exclude these deaths, the mortality rates fall to 38 deaths among 19,842 labors (1.9 per 1000) versus 10 deaths among 13,292 repeat cesareans (0.7 per 1000), or an absolute difference of 1.2 per 1000.

Comment: This study points out that systematic reviews also can have flaws. It also illustrates how odds ratios can give a misleading impression of the true risks. Even without correcting for deaths unrelated to birth route the alarming 70% increased risk of death of their odds ratio translates into just over 2 excess deaths in every 1000 planned VBACs. Moreover, this must be balanced against the permanent harm that may result from planned c-section. Here, 2.5 more women per 1000 having planned cesareans lost their ability to bear children because they had a hysterectomy. The authors acknowledge this point. The study concludes that because of the trade-offs in complications between the two delivery routes, “Either a trial of labor or elective repeat cesarean delivery may be a reasonable option for women with at least one previous cesarean delivery."