Obstetric anal sphincter injuries among women with gestational diabetes and women without gestational diabetes: A NSW population‐based cohort study

Background Obstetric anal sphincter injuries ( OASI s) are associated with maternal morbidity; however, it is uncertain whether gestational diabetes ( GDM ) is an independent risk factor when considering birthweight mode of birth and episiotomy. Aims To compare rates of OASI s between women with GDM and women without GDM by mode of birth and birthweight. To investigate the association between episiotomy, mode of birth and the risk of OASI s. Methods A population‐based cohort study of women who gave birth vaginally in NSW , from 2007 to 2013. Rates of OASI s were compared between women with and without GDM , stratified by mode of birth, birthweight and a multi‐categorical variable of mode of birth and episiotomy. Adjusted odds ratios ( aOR ) and 95% confidence intervals ( CI ) were calculated by multivariable logistic regression. Results The rate of OASI s was 3.6% (95% CI: 2.6–2.7) vs 2.6% (95% CI: 3.4–2.8; P  <   0.001) among women with and without GDM , respectively. Women with GDM and a macrosomic baby (birthweight ≥ 4000 g) had a higher risk of OASI s with forceps ( aOR 1.76, 95% CI: 1.08–2.86, P  =   0.02) or vacuum ( aOR 1.89, 95% CI: 1.17–3.04, P  =   0.01), compared with those without GDM . For primiparous women with GDM and all women without GDM , an episiotomy with forceps was associated with lower odds of OASI s than forceps only (primiparous GDM , forceps‐episiotomy aOR 2.49, 95% CI: 2.00–3.11, forceps aOR 5.30, 95% CI: 3.72–7.54), (primiparous without GDM , forceps‐episiotomy aOR 2.71, 95% CI: 2.55–2.89, forceps aOR 5.95, 95% CI: 5.41–6.55) and (multiparous without GDM , forceps‐episiotomy aOR 3.75, 95% CI: 3.12–4.50, forceps aOR 6.20, 95% CI: 4.96–7.74). Conclusion Women with GDM and a macrosomic baby should be counselled about the increased risk of OASI s with both vacuum and forceps. With forceps birth, this risk can be partially mitigated by performing a concomitant episiotomy.