Vaginal birth after cesarean: an appraisal of fetal risk

Abstract

Objective: To expand on prior investigations and further evaluate the fetal risk associated with vaginal birth after cesarean (VBAC) by examining the incidence not only of a depressed Apgar score at 5 minutes but also of fetal acidemia. Methods: Between January 1, 1991, and December 31, 1996, the following groups of patients who delivered a singleton fetus with birth weight greater than 750 g were identified: 2082 patients with one or more prior cesarean deliveries who were allowed a trial of labor, 1677 of whom delivered vaginally and 405 of whom delivered by repeat cesarean; 920 patients delivered by elective repeat cesarean; 22,863 patients without a prior cesarean who delivered vaginally; and 2432 patients delivered by primary cesarean after laboring. Umbilical cord arterial blood gases were obtained in 88.3% of these deliveries. Comparisons of Apgar scores at 5 minutes and umbilical cord arterial pH measurements were made between groups with χ 2 or Fisher exact test, and odds ratios (ORs) were calculated. Results: The only significant differences were noted between those patients who delivered vaginally after a prior cesarean and those patients who delivered vaginally without a prior cesarean. Neonates in the successful VBAC group were more likely to have an Apgar score at 5 minutes less than 7 (OR 1.52) or an umbilical arterial pH less than 7.1 (OR 1.69). Those neonates, however, were not at greater risk for an Apgar score less than 4 or a pH less than 7.0. Conclusion: Our experience suggests that VBAC poses a low level of fetal risk, although a much larger sample size would be required to exclude a two-fold increase in potentially damaging fetal acidemia.