Hormonal Contraception Use and Changes in Body Mass Index: A Cohort Study

Objective To examine the potential association between hormonal contraceptive use and body mass index (BMI). Design and Methods Linear regression model was used to assess change in BMI between adolescence and adulthood according to hormonal contraception use. Hormonal contraception (HC) use was categorized according to hormonal composition. Population We included all Danish women with data on adolescence height and weight in the Danish National Child Health register and adult weight and height reported in the Safe Choice survey. Main Outcome Measures The primary outcome was the difference in BMI from adolescence to adulthood, based on the assessed height and weight in adolescence and adulthood. Results We included 47 148 individuals with a median age of 21 years (1st‐3rd quantile: 19–24) at the time of answering the Safe Choice survey. Regardless of HC use, BMI increased between the two measurements for all groups. Hormonal contraception containing oestrogen was associated with a larger BMI increase after 4–5 years of cumulated duration of use compared to participants who had never used HC ( p ‐value < 0.001). After more than 5 years, among women with a history of HC use, BMI increased most in users of combined oestrogen–progestin contraceptives (3.14 BMI points; 95% CI: 2.98–3.30; p < 0.001) and least in progestin‐only users (2.47 BMI points; 95% CI: 2.27–2.66; p < 0.001); in comparison, non‐users experienced a BMI increase of 2.28 BMI points (95% CI: 2.10–2.45; p < 0.001). Conclusion This study shows that BMI increased between the two measurements in all groups. Hormonal contraception containing oestrogen was associated with a larger BMI increase after 4–5 years of cumulative HC use compared to never‐users. Among those with a cumulative duration of HC use greater than five years, the largest BMI increase was observed for combined HC, and the smallest was observed for progestin‐only methods.