Morphological and functional features of endometrial decidualization following long-term intrauterine levonorgestrel delivery

Irregular bleeding remains a common reason for the discontinuation ofprogestin-only contraception. The levonorgestrel releasing intrauterinesystem (LNG-IUS) has profound morphological effects upon the endometrium.Specific features are gland atrophy and extensive decidual transformationof the stroma. Morphological changes in the endometrium may be associatedwith perturbation of mechanisms regulating normal endometrial function.This study describes endometrial stromal and glandular features prior toand up to 12 months following insertion of the LNG-IUS. Comparison is madewith first trimester decidua. In order to elucidate further mechanismsgoverning endometrial function with local intrauterine delivery of LNG, wehere report histological features consistent with decidualization; asignificant increase in granulocyte-macrophage colony stimulating factor(GM-CSF) immunoreactivity in decidualized stromal cells; glandular andstromal prolactin receptor expression and an infiltrate of CD56 + largegranular lymphocytes and CD68 + macrophages. We are unaware of previousreports which have documented longitudinally both morphological andfunctional observations in endometrium exposed to local intrauterinelevonorgestrel delivery. These studies demonstrate that long-termadministration of intrauterine levonorgestrel results in features ofaltered morphology and function. No correlation was apparent between theend points in the study and the bleeding patterns described by thesubjects. Further evaluation of these features in the context of menstrualbleeding experience may contribute to a better understanding of thistroublesome side-effect which often leads to dissatisfaction anddiscontinuation of the intrauterine system.