Purpose: To evaluate the impact of maternal obesity on labour, intrapartual assessment and delivery. Methods: Retrospective cohort analysis of n = 11,681 deliveries supervised between 01 January 2000 and 31 December 2009. Results were analysed dividing the patients into two main groups according to their body mass index (BMI): group 1, control: BMI 18-24.9 and group 2 BMI, test >25. Subgroups were built: (0) BMI 25-29.9, (I) BMI 30-34.9, (II) BMI 35-39.9, (III) BMI >40. Exclusion criteria were defined as: delivery <37 + 0 weeks p.m., multiple pregnancy, comorbidity other than GDM, abnormal presentation, BMI <18.5, and incomplete data. The main outcome parameter was defined as secondary caesarean delivery rate and mode of delivery. Results: N = 8,379 patients met the inclusion criteria and were divided in two groups: 1, n = 4,464 patients and 2, n = 3,915. Basic maternal characteristics including foetal vital parameters were equal in all groups. GDM occurred more frequently in obese patients (P < 0.001). For the main outcome parameter a significant decrease in the rate of spontaneous delivery between control/test groups (72-66%, P < 0.001) and control/I-III groups (72 vs. 50%, P < 0.001) could be observed. The rate of secondary c-section increased significantly according to a higher BMI (>40: OR 2.5, 95% CI 1.84-3.61, χ 2 P < 0.001). The groups showed no difference in the rate of injuries during delivery though foetal birth weight increased significantly with a higher BMI (3,412-3,681 g; P < 0.001). Conclusion: Obesity decreases the chance to deliver spontaneously. Moreover, the obese patient suffers from a significantly longer trial of labour (7.9 vs. 9.5 h) and an elevated risk of surgical delivery.