Variations in the use of oxytocin for augmentation of labour in Sweden: a population-based cohort study.

National Swedish data shows substantial variation in the use of oxytocin for augmentation of spontaneous labour between obstetric units. This study aimed to investigate if variations in the use of oxytocin augmentation are associated with maternal and infant characteristics or clinical factors. We used a cohort design including women allocated to Robson group 1 (nulliparous women, gestational week ≥ 37 + 0, with singleton births in cephalic presentation and spontaneous onset of labour) and 3 (parous women, gestational week ≥ 37 + 0, with singleton births in cephalic presentation, spontaneous onset of labour, and no previous caesarean birth). Crude and adjusted logistic regression models with marginal standardisation were used to estimate risk ratios (RR) and risk differences (RD) with 95% confidence intervals (CI) for oxytocin use by obstetric unit. An interaction analysis was performed to investigate the potential modifying effect of epidural. The use of oxytocin varied between 47 and 73% in Robson group 1, and 10% and 33% in Robson group 3. Compared to the remainder of Sweden, the risk of oxytocin augmentation ranged from 13% lower (RD - 13.0, 95% CI - 15.5 to - 10.6) to 14% higher (RD 14.0, 95% CI 12.3-15.8) in Robson group 1, and from 6% lower (RD - 5.6, 95% CI - 6.8 to - 4.5) to 18% higher (RD 17.9, 95% CI 16.5-19.4) in Robson group 3. The most notable differences in risk estimates were observed among women in Robson group 3 with epidural. In conclusion, variations in oxytocin use remained despite adjusting for risk factors. This indicates unjustified differences in use of oxytocin in clinical practice.