Women with pregestational diabetes have increased rates of adverse obstetric and perinatal outcomes, including congenital malformations, preeclampsia, stillbirth, fetal macrosomia, and caesarean delivery compared to women without diabetes. The risk of emergency caesarean section (CS) is 3–4 times higher compared to women without diabetes and despite therapeutic initiatives and technological advancements, the overall CS rate in women with pregestational diabetes remains persistently above 60%. A common indication for elective CS in women with pregestational diabetes is macrosomia. It is essential to specifically investigate active labour duration in a well-defined cohort of women with pregestational diabetes and to include emergency CS in order to explore whether prolonged labour contributes to the elevated CS risk in this population. Authors hypothesised that pregestational diabetes is associated with longer duration of active labour, in addition to other known factors influencing labour progression. Therefore, the aims of this study were to evaluate the impact of pregestational diabetes on DAL in nulliparous women in induced and spontaneous onset of labour and to compare CS indications and rates, -both elective and emergency, -with those of women without diabetes. It was a population-based cohort study in Sweden. 243 537 nulliparous women, registered in the Swedish Pregnancy Register, who delivered a singleton fetus at ≥34+0 gestational weeks+days between 2014 and 2020 were included. Women with gestational diabetes mellitus were excluded. Women with pregestational diabetes had longer active labour and a reduced chance of vaginal delivery at a given time point compared to women without diabetes, adjusted hazard ratio 0.65 (p <0.001). Among those with spontaneous labour, median DAL in diabetic vs. non-diabetic women was 9.60 h versus 8.75 h, difference 0.85 h, p <0.001. Corresponding numbers for induced labours were 8.92 h versus 7.20 h, difference 1.72 h, p<0.001. Elective and emergency CS rates were higher in women with pregestational diabetes than non-diabetic women (7.4% and 29.4% vs. 2.6% and 7.1% respectively), with suspected macrosomia (50.4%) and fetal distress (31.9%) being the most common indications for CS among women with pregestational diabetes. In this nation-wide population-based cohort of nulliparous women, we observed a longer duration of both spontaneous and induced active labour in women with pregestational diabetes, as well as a reduced likelihood of vaginal delivery at any given time during active labour, compared with women without diabetes. The prolonged labour duration in women with pregestational diabetes highlights the significance of the labour ward staff's support and patience in managing diabetic parturients, potentially allowing more time before diagnosing labour dystocia in this population. An extended period of active labour may influence how women perceive their birth experience and emphasises the importance of providing these women with comprehensive information prior to labour. Source: Sofia Nevander, Sara Carlhäll, Karin Källén; BJOG: An International Journal of Obstetrics & Gynaecology, 2025; 0:1–9 https://doi.org/10.1111/1471-0528.18276