First Vaginal Birth after Cesarean: a retrospective cohort study

Objective: The main aim of this study was to explore the course of labor and
extent of perineal trauma at the first vaginal birth after cesarean section
(fVBAC) in comparison to primiparous vaginal birth (PVB) in women without
epidural analgesia.

Study design: All fVBACs without epidural analgesia and the subsequent PVBs (controls)
between 2012 - 2016 were included in this retrospective cohort study. Data were
collected from health records and included maternal characteristics and labor
details in both groups as well as cervical dilation at the time of previous
cesarean in fVBAC group.

Results: The study comprised 510 women; 255 fVBACs and 255 controls. The majority
of fVBACs were after a pre-labor cesarean section – 177 (69.4%). There was a
statistically significant difference in the recorded duration of first stage
between the fVBACs and controls (289 vs. 347min respectively, p<.001). Women
were less likely to have an intact perineum in the fVBAC group (29.8 vs. 43.1%,
p<0.01), however, there was no statistically significant difference in anal
sphincter injury rates between both groups (2.3 vs. 1.9%, p=0.76). The groups
differed in rates of cervical tears requiring suturing (21.2 vs. 12.9%,
p=0.01). On further subgroup analysis, the duration of first stage of labor
shorter in women who previously had a caesarean section late in labor (≥ 8cm
cervical dilatation) compared to a pre-labor cesarean section (uneffaced
cervix), however, there were no differences in other outcomes.

Conclusion: Compared to primiparous women having a vaginal birth, women having
their first vaginal birth after a cesarean section have a shorter 1st
stage of labor, a higher risk of sustaining cervical lacerations and perineal
trauma. However, the risk of anal sphincter injury does not seem to be
increased.