Background
For women considering vaginal birth after caesarean section (VBAC), obesity has been associated with a lower rate of vaginal birth and a higher rate of uterine rupture. To enhance antenatal counselling, this study aimed to evaluate the success rates of morbidly obese women undergoing a trial of labour (TOL).

Method
A retrospective analysis was performed of women who birthed at our hospital who had previously had one caesarean section. Routinely collected data were reviewed for mode of birth for women who underwent a TOL. A number of maternal and neonatal outcomes were also gathered. The data were analysed according to those women with a body mass index (BMI) equal to or above 40, compared to those women with a BMI below 40.

Results
From 2011 to 2018, 2097 women gave birth at our hospital and had a caesarean section for a prior pregnancy. Of these women, 1234 (58.9%) had an elective caesarean section and 863 (41.1%) underwent a TOL. Of the women undertaking a TOL, 73.1% gave birth vaginally. Women with a BMI equal to or greater than 40 were less likely to have a successful VBAC compared to women with a BMI less than 40 (58.9% vs 74.1%, P = 0.013). Only 50% of women with a BMI equal to or greater than 40 had a successful VBAC if they had not previously had a vaginal birth.

Conclusion
Women with a BMI over 40 had lower rates of successful VBAC. Rates were even lower for those who had not had a prior vaginal birth.