Development of the Er-Kay Classification: A Novel Volume-Based Assessment of Cesarean Scar Defects and Their Association with Abnormal Uterine Bleeding

<b>Objective:</b> This study aimed to determine the prevalence of isthmocele in patients who had undergone cesarean delivery and to investigate its association with abnormal uterine bleeding (AUB). Additionally, a novel volume-based classification system (Er-Kay Classification) was developed to provide a more precise assessment of cesarean scar defects and their correlation with clinical symptoms. <b>Material and Methods:</b> This retrospective, hospital-based cohort study was conducted at Ankara Etlik Zübeyde Hanım Women's Health Training and Research Hospital between October 2017 and March 2018. A total of 1098 patients who had undergone cesarean delivery and attended follow-up visits were included. Patients were categorized based on the presence of isthmocele (study group: n = 134) and its absence (control group: n = 964). Isthmocele volume was calculated using the formula (Height × Width × Depth)/3, and patients were classified as Grade 1 (≤50 mm³) or Grade 2 (>50 mm³) based on the novel Er-Kay Classification. Clinical symptoms, including AUB (pre-, inter-, postmenstrual bleeding), dysmenorrhea, dyspareunia, and postcoital bleeding, were compared between groups. Statistical analyses were performed using SPSS 27.0 (NY, USA),with a significance level of <i>p</i> < 0.05. <b>Results:</b> The prevalence of isthmocele was 12.2% (134/1098). Patients with isthmocele had significantly shorter menstrual cycles compared to those without (26.64 ± 5.35 vs. 28.08 ± 4.97 days, <i>p</i> = 0.038). Postmenstrual bleeding (47.0% vs. 4.7%, <i>p</i> < 0.001), dysmenorrhea (38.8% vs. 18.3%, <i>p</i> < 0.001), and dyspareunia (39.6% vs. 14.7%, <i>p</i> < 0.001) were significantly more frequent in the isthmocele group. According to the Er-Kay Classification, intermenstrual bleeding was significantly higher in Grade 2 (23.1%) than in Grade 1 (4.3%) (<i>p</i> = 0.001). Similarly, postmenstrual bleeding was more common in Grade 2 (56.9%) than in Grade 1 (37.7%) (<i>p</i> = 0.026). No significant differences were found for premenstrual bleeding, dysmenorrhea, or dyspareunia between the Er-Kay Classification groups (<i>p</i> > 0.05). <b>Conclusions:</b> The findings indicate that isthmocele is significantly associated with AUB, dysmenorrhea, and dyspareunia. The Er-Kay Classification, based on isthmocele volume, provides a more precise assessment of symptom severity, particularly in intermenstrual and postmenstrual bleeding cases. These results suggest that volume-based evaluations should be incorporated into clinical practice for better patient management and diagnosis of cesarean scar defects.