Prospective study of the forearm bone mineral density of long-term users of the levonorgestrel-releasing intrauterine system.

BACKGROUND

The levonorgestrel-releasing intrauterine system (LNG-IUS) induces amenorrhoea, and its effect on bone mineral density (BMD) may constitute a concern. This study evaluated BMD in long-term users of the LNG-IUS or intrauterine device (IUD).

METHODS

BMD was evaluated at the midshaft of the ulna and ultra-distal radius using dual-energy X-ray absorptiometry in 37 women at 7 or 10 years of use following placement of a second LNG-IUS. The groups were paired for duration of use, age, body mass index (BMI), ethnicity and number of pregnancies.

RESULTS

The mean age of both LNG-IUS and IUD users at the 7th and 10th year was approximately 34 and 38 years, respectively. Mean BMI was approximately 25 in both groups, increasing to approximately 26 at the 10th year. Amenorrhoea occurred in 51.4 and 91.9% of LNG-IUS users at the 7th and 10th year, respectively. Estradiol levels in LNG-IUS users were normal at both evaluations. There were no differences in BMD (g/cm(2)) at the midshaft of the ulna nor ultra-distal radius between LNG-IUS and IUD users or between the 7th and 10th years of use in LNG-IUS users. A Z-score below -2SD at the ultra-distal radius was observed in only one LNG-IUS user and in none of the IUD users at the 10th year. Higher BMI and BMD at the seventh year and amenorrhoea were predictors of higher BMD at the 10th year.

CONCLUSIONS

BMD at the midshaft of the ulna and ultra-distal radius in LNG-IUS users were similar to that of IUD users and remained unchanged between the 7th and the 10th years of use.