Women birthing vaginally after a prior C-section are 21% more likely to sustain a severe perineal tear than primiparous women having vaginal births, Australian clinicians warn.

Their findings, based on data from 130,000 parous women, suggest the need to update antenatal counselling to better reflect the risk of obstetric anal sphincter injury (OASI), they say.

The researchers, led by obstetrician Dr Anthea Lindquist from Melbourne’s Mercy Hospital for Women, warned that despite the significant baseline risk of OASI, the issue was “only peripherally acknowledged in many professional guidelines”.

In a retrospective cohort study, the team compared the risk of OASI between 5400 women who had a vaginal birth after caesarean (VBAC) and 123,500 primiparous women who birthed vaginally in Victoria from 2009-2014.