Abstract Objective Clinical reasoning is an essential skill, the foundations of which should be acquired during medical school. Within the format of test-based learning, such examinations can also be used to support the long-term retention of procedural knowledge necessary for clinical reasoning. The aim was to investigate whether repeated exposure to clinical cases in obstetrics and gynecology (OBGYN) with built-in questions leads to higher learning outcome than pure reading cases and what influence the delay between the intervention and the final test has on the retention of the respective content. Methods In this non-randomised crossover study, 5th-year medical students (duration of the study is 6 years) taking a 1-week clinical attachment in OBGYN participated in computer-based case seminars in winter term 2020/2021, in which different case histories on gynecological-obstetric diseases were presented. Case content was identical for all groups, but the presentation format (cases with key feature questions vs read-only cases) of individual case vignettes changed weekly. The also intervention was repeated after 2 weeks for each group. Knowledge was assessed in an entry and an exit exam consisting of 40 short-answer questions. Results A total of 94 out of 118 eligible students participated in the study (response rate: 79.7%). Learning outcome was significantly higher for items presented in the key feature format compared to items presented as read-only cases (74.2 ± 8.6% vs. 71.0 ± 9.2%; p = 0.017). Furthermore, the analysis showed that the temporal distance of the intervention package from the final examination had no influence on retention. Conclusion This is the first study to demonstrate an effect of test-enhanced learning on clinical reasoning in the subject of OGBYN. In this cross-over study, repeated testing was more effective than repeated case-based learning alone. Curricular implementation of longitudinal key feature testing can thus improve learning outcomes for OBGYN.