Temporal changes in cervical mucus after insertion of the levonorgestrel-releasing intrauterine system.

Background: The major contraceptive action of the levonorgestrel-releasing intrauterine system (LNG-IUS) is cervical mucus (CM) thickening, which prevents sperm penetration. No study to date has examined the temporal relationship between the insertion of the LNG-IUS and changes in CM quality and sperm penetration.

Study Design: Participants were enrolled in a clinically descriptive study to compare the quality of CM and three parameters of sperm penetration prior to insertion of the LNG-IUS and on Days 1, 3 and 5 after insertion. Measurements of estradiol, progesterone and levonorgestrel (LNG) in serum and LNG in CM were also carried out at these times. CM was analyzed using the World Health Organization CM grading criteria. Sperm penetration was determined using an in vitro sperm-CM penetration test.

Results: All 10 participants underwent LNG-IUS insertion during midcycle when CM quality was good and sperm penetration was excellent. On Day 1 after LNG-IUS insertion, the majority of participants demonstrated poor CM quality and poor sperm penetration. On Day 3, all participants had poor CM quality, and all but one subject had poor sperm penetration. By Day 5, all participants had poor CM quality and poor sperm penetration. LNG levels in CM peaked on the day after LNG-IUS insertion.

Conclusion: Significant changes in quality of CM and sperm penetration were observed shortly after LNG-IUS insertion; however, CM can remain penetrable for up to 5 days when the LNG-IUS is inserted midcycle.