AbstractIntroductionWomen with gestational diabetes mellitus (GDM) have higher rates of adverse perinatal outcomes compared with women without GDM, including an increased risk for having labor induced and for cesarean section. The findings from previous studies analyzing duration of labor in women with GDM are contradictory.The aim of the study was to evaluate the impact of GDM on time in spontaneous and induced active labor.Material and methodsThis was a population‐based cohort study including 247 524 primiparous women who gave birth to a singleton fetus with cephalic presentation, ≥34⁺⁰ (completed gestational weeks + additional days) between January 2014 and May 2020 in Sweden. Data was obtained from the Swedish Pregnancy Register. Time in active labor was compared between women with GDM and without GDM with a spontaneous labor onset or induction of labor using Kaplan Meier survival analysis and Cox regression analysis.ResultsWomen with GDM had significantly longer time in active labor, both with a spontaneous onset and induction of labor compared to women without GDM. Women with GDM had a decreased chance of vaginal delivery at a certain time‐point compared to women without GDM, with adjusted hazard ratio of 0.92 (0.88–0.96) and 0.83 (0.76–0.90) for those with spontaneous onset and induction of labor, respectively. Women with GDM had increased risk for time in active labor ≥12 h both in spontaneous labor onset (adjusted odds ratio 1.14 [1.04–1.25]) and in induction of labor (adjusted odds ratio 1.55 [1.28–1.87]).ConclusionsWomen with GDM seem to spend a longer time in active labor, both in spontaneous and induced active labor compared to women without GDM. To be able to individualize care intrapartum, there is a need for more studies demonstrating the impact of hyperglycemia during pregnancy on outcomes during childbirth.