Ischemic Stroke in Users of Combined Hormonal Contraceptives: A Danish Registry Study.

Background: The combined hormonal contraceptive (CHC) with ethinylestradiol and progestins is the most widely used contraceptive method among young women and is used by millions worldwide. However, uncertainties exist about the risk of ischemic stroke associated with the use of CHCs with low-dose ethinylestradiol (<50-µg ethinylestradiol) and with the newest fourth-generation progestins that have only been sparsely investigated for the risk of ischemic stroke.

Methods: In this cohort study based on Danish registries covering the entire Danish female population aged 18 to 49 years from 2004 to 2021, we investigated incidence rate ratios (IRRs) of ischemic stroke using CHCs compared with nonuse of hormonal contraceptives. Analyses focused on comparing CHCs based on ethinylestradiol content (30-40- versus ≤20-μg ethinylestradiol), progestin generation (second, third, and fourth) in CHCs, and route of administration (monophasic versus sequential). Poisson regression models adjusting for age, education, ethnicity, calendar year, and medication used for risk factors were utilized.

Results: In total, 1 711 757 nonpregnant women contributed 14 697 788 person-years to the investigation. For users of CHCs containing <50-µg ethinylestradiol, the adjusted IRR was increased by 1.77 (95% CI, 1.62-1.93) compared with nonusers of hormonal contraceptives. IRR did not differ between CHCs with 30- to 40- and ≤20-µg ethinylestradiol. Adjusted incidence rate difference between CHC users and nonusers of hormonal contraceptives ranged from 1 in 100 000 women per year in 18 to 24 years of age to 24 in 100 000 women per year in ≥45 years of age. Incidence rate in users of fourth-generation CHCs was 30% lower than that of second-generation CHCs adjusted IRR (0.70 [95% CI, 0.50-0.98]). IRR for users of third-generation CHCs did not differ significantly from that of second-generation users adjusted IRR (1.14 [95% CI, 0.97-1.35]).

Conclusions: Use of CHCs was associated with a 1.77 higher IRR of ischemic stroke. IRR did not relate to ethinylestradiol content in users of CHCs with <50-µg ethinylestradiol. IRR was 30% lower in users of fourth-generation than in users of second-generation CHCs.