Comparison of ovarian cyst formation in women using the levonorgestrel-releasing intrauterine system vs. hysterectomy.

OBJECTIVE

To analyze the effect of the levonorgestrel-releasing intrauterine system (LNG-IUS) on ovarian cyst formation, endometrial thickness and the size of uterus and uterine fibroids by ultrasonography.

SUBJECTS AND METHODS

This was a prospective, randomized trial comparing the LNG-IUS and hysterectomy in 236 women (age range 35-49 years) referred for menorrhagia. Transvaginal ultrasound examination was used to study the presence of ovarian cysts, uterine size, endometrial thickness, and the size of the uterus and uterine fibroids during a 12-month follow-up period.

RESULTS

At baseline examination, 12 ovarian cysts were detected, eight in the LNG-IUS group and four in the hysterectomy group. During the follow-up period, 14 new cysts had emerged at 6 months and 14 new cysts had emerged at 12 months in the LNG-IUS group, whereas the corresponding figures in the hysterectomy group were three and eight, respectively. All but one of the 14 new cysts (94.1%) detected at 6 months in the LNG-IUS group resolved spontaneously, whereas two out of the eight cysts detected at the baseline examination persisted for 12 months. Three cysts were removed at operation. The relative risk of the occurrence of ovarian cysts was significantly higher in women with LNG-IUS, compared with women who underwent hysterectomy. LNG-IUS did not affect the size of the uterus or uterine fibroids, but it was associated with a decrease in endometrial thickness. The occurrence of cysts did not correlate with age or follicle stimulating hormone levels, but a weak positive correlation between the occurrence of cysts and the presence of irregular bleeding was observed.

CONCLUSIONS

LNG-IUS use in the treatment of menorrhagia was associated with the development of ovarian cysts, but these were symptomless and showed a high rate of spontaneous resolution. LNG-IUS did not affect the size of the uterus or the size of uterine fibroids, but decreased the thickness of the endometrium.