Vaginal birth after cesarean: an appraisal of fetal risk

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.

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 chi2 or Fisher exact test, and odds ratios (ORs) were calculated.

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.

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.