Interpretation
Our study has strong clinical relevance. We set out to validate the
association between VBAC and significant perineal injury using a large
cohort, and have demonstrated with updated methodology that women having
a VBAC are 21% more likely than primiparous women to sustain a
3rd or 4th degree tear during
vaginal birth. Current antenatal counselling and patient education for
women attempting a VBAC typically focusses on the risk of uterine
rupture and subsequent fetal complications (17, 18), often without any
reference to the increased risk of obstetric anal sphincter injury. In
light of our findings, we feel the evidence now convincingly
demonstrates an increased risk of significant perineal injury associated
with VBAC. We suggest that this risk should be included in the antenatal
counselling of women considering a VBAC and be acknowledged in the
guidelines of peak professional bodies such as the Royal Australian and
New Zealand College of Obstetricians and Gynaecologists and the Royal
College of Obstetricians and Gynaecologists.
Our study is well-timed with many Western jurisdictions introducing
initiatives to prevent and reduce the occurrence of
3rd and 4th degree tears. Through
measures such as timely mediolateral episiotomy and Manual Perineal
Protection, the OASI Care Bundle, introduced throughout the UK in
2016-2017, was shown to significantly reduce the risk of
3rd and 4th degree tears (aOR 0.80;
95%CI 0.65-0.98) in participating units (39). In Victoria, Australia,
there is a current state-wide initiative to reduce the rate of
3rd and 4th degree tears amongst all
women having a vaginal birth (the Better births for women
collaborative ), instigated in 2019 by the peak safety and quality
institution, Safer Care Victoria (40). Neither the OASI Care Bundle in
the UK or the Better Births initiative in Australia identified women
having VBAC as a high-risk group, however our findings suggest that
these women should be prioritised in such initiatives.
Our intention in pursuing this study was not to dissuade either patients
or healthcare providers from supporting women attempting a vaginal birth
after caesarean section, but rather to make antenatal counselling more
comprehensive, birth management decisions better informed and to help
optimise intrapartum care. There are myriad benefits associated with
successful, uncomplicated VBAC, some of which include expedited
post-birth recovery and improved breastfeeding initiation (41, 42).
Vaginal birth after caesarean section also avoids the well-established
risks related to repeat caesarean section delivery, such as significant
bleeding, development of abdominal adhesions, increased future risk of
placenta praevia, disorders of placental adherence and unnecessary
iatrogenic preterm birth in the setting of threatened preterm labour
(43, 44).