When Ultrasound and Hysterometry Disagree: Challenges in Levonorgestrel-Releasing Intrauterine System Placement.

Insertion of a levonorgestrel-releasing intrauterine system (LNG-IUS) may be technically challenging in women with altered uterine anatomy or difficult cervical access. We report the case of a 24-year-old nulligravid woman with obesity and a subdermal contraceptive implant who sought transition to an LNG-IUS. Pre-procedural transvaginal ultrasound (TVUS) demonstrated a retroverted uterus with apparently normal uterine dimensions. However, during insertion, hysterometry measured approximately 4 cm, raising concern regarding a reduced uterine cavity and possible perforation risk. The procedure was interrupted. After cervical priming with misoprostol, following insertion was successfully performed. Follow-up TVUS confirmed correct positioning of the device near the uterine fundus. This case highlights the potential discrepancy between anatomical uterine measurements obtained by ultrasound and functional assessment of the uterine cavity during instrumentation in retroflexed uteri and reinforces the importance of individualized contraceptive counseling and procedural caution in the primary care setting.