Uterine transverse diameter and risk of LNG-IUS malposition in adenomyosis patients: a threshold effect analysis from a retrospective cohort study.

Objective: The malposition of the levonorgestrel-releasing intrauterine system (LNG-IUS) can have a considerable impact on the treatment outcomes for patients with adenomyosis. This study was designed to explore the relationship between the transverse diameter of the uterus and the occurrence of LNG-IUS malposition.

Methods: This retrospective cohort study enrolled 99 adenomyosis patients treated at Fujian Maternity and Child Health Hospital between May 2021 and May 2023. Preoperative uterine transverse diameter was measured using transvaginal ultrasound examinations. We defined LNG-IUS malposition as either downward displacement or expulsion of the device. Data analysis employed Cox regression models with adjustments for relevant demographic, clinical, and laboratory variables.

Results: Our analysis revealed a notable non-linear relationship between the transverse diameter of the uterus and subsequent risk of LNG-IUS malposition. We identified 5.4 cm as a significant clinical threshold; beyond this measurement, the risk increased substantially, with malposition hazard rising by 112% per additional centimeter (HR 2.12; 95% CI, 1.28-3.49; p = 0.003). Among the subgroup of patients suffering from severe dysmenorrhea (VAS ≥ 7), this association was considerably stronger, yielding a hazard ratio of 3.43 (95% CI, 1.32-8.89; p = 0.011).

Conclusion: Patients with adenomyosis whose uterine transverse diameter exceeds 5.4 cm face a higher risk of LNG-IUS malposition. This measurement threshold provides clinicians a practical tool for assessing suitable candidates for LNG-IUS placement, which may lead to better outcomes in this patient group.