Body weight and composition in users of levonorgestrel-releasing intrauterine system.

Background: There is little information about body weight and body composition (BC) among users of the levonorgestrel-releasing intrauterine system (LNG-IUS). The aim of this study was to evaluate body weight and BC in LNG-IUS users compared to users of the TCu380A intrauterine device (IUD).

Study Design: A prospective study was done with 76 new users of both contraceptive methods. Women were paired by age (±2 years) and body mass index (BMI, kg/m², ±2). Body weight and BC (% lean mass and % fat mass) were evaluated by a trained professional at baseline and at 1 year of contraceptive use. The BC measurements were obtained using Lunar DXA equipment. Weight and BC were evaluated in each woman at baseline and at 12 months and analyzed as the mean change within each woman. Then, the changes in weight and BC for each woman were calculated and then compared between LNG-IUS and TCu380A IUD users (paired data for each woman). The central-to-peripheral fat ratio was calculated by dividing trunk fat by the upper and lower limb fat.

Results: There were no significant differences at time of IUD insertion between LNG-IUS and TCu380A IUD users regarding age (mean±SD) (34.4±7.5 vs. 33.9±8.0 years), BMI (25.3±4.1 vs. 25.9±4.1) and number of pregnancies (1.9±0.2 vs. 1.7±0.2), respectively. Mean body weight gain of 2.9 kg was observed among LNG-IUS users at 12 months (p=.0012), whereas the body weight of TCu380A IUD users only increased by 1.4 kg (p=.067). There was no significant difference in body weight change between the two groups of users at 12 months. The variation in the central-to-peripheral fat ratio was the same between the two groups (-1.6% vs. -0.2%; p=.364). LNG-IUS users showed a 2.5% gain in fat mass (p=.0009) and a 1.4% loss of lean mass, whereas TCu380A IUD users showed a loss of 1.3% of fat mass (p=.159) and gain of 1.0% of lean mass (p=.120). TCu380A IUD users gained more lean mass than LNG-IUS users (p=.0270), although there was no significant difference between the two groups after 12 months of use.

Conclusions: Although an increase in mean fat mass among LNG-IUS users at 12 months of use was observed, it should be noted that an increase of body weight was also observed in both groups after 1 year of insertion of the device. However, a study with a larger number of women and long-term evaluation is necessary to evaluate these body changes.