Effects on bone mineral density of a monophasic combined oral contraceptive containing nomegestrol acetate/17β-estradiol in comparison to levonorgestrel/ethinylestradiol.

OBJECTIVE: To compare the effects of a monophasic combined oral contraceptive containing nomegestrol acetate/17β-estradiol (NOMAC/E2) on bone mineral density with a combined oral contraceptive containing levonorgestrel/ethinylestradiol (LNG/EE).

DESIGN: Prospective, randomized, open-label, comparative clinical study.

SETTING: Gynecology center in Norway.

POPULATION: One hundred and ten women (20-35 years old) actively seeking contraception. Methods. For 26 consecutive 28-day cycles, women received one of the following two treatments: NOMAC/E2 (2.5 mg/1.5 mg) in a 24/4-day regimen (n= 56); or LNG/EE (150 μg/30 μg) in a 21/7-day regimen (n= 54). Main outcome measures. Bone mineral density of the lumbar spine, femoral neck, hip and trochanter (measured by dual energy X-ray absorptiometry); associated z-scores of the lumbar spine and femoral neck.

RESULTS: In NOMAC/E2 users, mean (±SD) z-score change from baseline for lumbar spine and femoral neck were 0.019 ± 0.242 and -0.007 ± 0.228, respectively, vs. 0.121 ± 0.269 and 0.044 ± 0.253 in LNG/EE users, respectively. Differences between treatment groups were not significant (p= 0.19 and p= 0.57, respectively). There were no significant differences between changes in hip and trochanter z-scores between NOMAC/E2 and LNG/EE treatments.

CONCLUSIONS: After two years, NOMAC/E2 had no clinically relevant effect on bone mineral density. No significant difference in the effect on bone mineral density between NOMAC/E2 and LNG/EE was observed.