Venous Thrombosis in Users of Non-Oral Hormonal Contraception
Venous Thrombosis in Users of Non-Oral Hormonal Contraception
Objective To assess the risk of venous thrombosis in current users of non-oral hormonal contraception.
Design Historical national registry based cohort study.
Setting Four national registries in Denmark.
Participants All Danish non-pregnant women aged 15-49 (n=1,626,158), free of previous thrombotic disease or cancer, were followed from 2001 to 2010.
Main outcome measures Incidence rate of venous thrombosis in users of transdermal, vaginal, intrauterine, or subcutaneous hormonal contraception, relative risk of venous thrombosis compared with non-users, and rate ratios of venous thrombosis in current users of non-oral products compared with the standard reference oral contraceptive with levonorgestrel and 30-40 µg oestrogen. Diagnoses were confirmed by at least four weeks of anticoagulation therapy after the diagnosis.
Results Within 9,429,128 woman years of observation, 5287 first ever venous thrombosis events were recorded, of which 3434 were confirmed. In non-users of hormonal contraception the incidence rate of confirmed events was 2.1 per 10,000 woman years. Compared with non-users of hormonal contraception, and after adjustment for age, calendar year, and education, the relative risk of confirmed venous thrombosis in users of transdermal combined contraceptive patches was 7.9 (95% confidence interval 3.5 to 17.7) and of the vaginal ring was 6.5 (4.7 to 8.9). The corresponding incidences per 10,000 exposure years were 9.7 and 7.8 events. The relative risk was increased in women who used subcutaneous implants (1.4, 0.6 to 3.4) but not in those who used the levonorgestrel intrauterine system (0.6, 0.4 to 0.8). Compared with users of combined oral contraceptives containing levonorgestrel, the adjusted relative risk of venous thrombosis in users of transdermal patches was 2.3 (1.0 to 5.2) and of the vaginal ring was 1.9 (1.3 to 2.7).
Conclusion Women who use transdermal patches or vaginal rings for contraception have a 7.9 and 6.5 times increased risk of confirmed venous thrombosis compared with non-users of hormonal contraception of the same age, corresponding to 9.7 and 7.8 events per 10,000 exposure years. The risk was slightly increased in women using subcutaneous implants but not in those using the levonorgestrel intrauterine system.
Several studies have assessed the risk of venous thrombosis in women using oral contraceptives. However, none has assessed the risk in women using subcutaneous hormonal implants. A recent study reported a 48% higher risk of venous thrombosis in women using a vaginal ring compared with those using combined oral contraceptives containing levonorgestrel, and a few studies have reported the risk in women using a transdermal combined contraceptive patch, although the results were conflicting.
Using a historical national registry based cohort study design, we assessed the absolute and relative risk of venous thrombosis in Danish women using non-oral hormonal contraception.
Abstract and Introduction
Abstract
Objective To assess the risk of venous thrombosis in current users of non-oral hormonal contraception.
Design Historical national registry based cohort study.
Setting Four national registries in Denmark.
Participants All Danish non-pregnant women aged 15-49 (n=1,626,158), free of previous thrombotic disease or cancer, were followed from 2001 to 2010.
Main outcome measures Incidence rate of venous thrombosis in users of transdermal, vaginal, intrauterine, or subcutaneous hormonal contraception, relative risk of venous thrombosis compared with non-users, and rate ratios of venous thrombosis in current users of non-oral products compared with the standard reference oral contraceptive with levonorgestrel and 30-40 µg oestrogen. Diagnoses were confirmed by at least four weeks of anticoagulation therapy after the diagnosis.
Results Within 9,429,128 woman years of observation, 5287 first ever venous thrombosis events were recorded, of which 3434 were confirmed. In non-users of hormonal contraception the incidence rate of confirmed events was 2.1 per 10,000 woman years. Compared with non-users of hormonal contraception, and after adjustment for age, calendar year, and education, the relative risk of confirmed venous thrombosis in users of transdermal combined contraceptive patches was 7.9 (95% confidence interval 3.5 to 17.7) and of the vaginal ring was 6.5 (4.7 to 8.9). The corresponding incidences per 10,000 exposure years were 9.7 and 7.8 events. The relative risk was increased in women who used subcutaneous implants (1.4, 0.6 to 3.4) but not in those who used the levonorgestrel intrauterine system (0.6, 0.4 to 0.8). Compared with users of combined oral contraceptives containing levonorgestrel, the adjusted relative risk of venous thrombosis in users of transdermal patches was 2.3 (1.0 to 5.2) and of the vaginal ring was 1.9 (1.3 to 2.7).
Conclusion Women who use transdermal patches or vaginal rings for contraception have a 7.9 and 6.5 times increased risk of confirmed venous thrombosis compared with non-users of hormonal contraception of the same age, corresponding to 9.7 and 7.8 events per 10,000 exposure years. The risk was slightly increased in women using subcutaneous implants but not in those using the levonorgestrel intrauterine system.
Introduction
Several studies have assessed the risk of venous thrombosis in women using oral contraceptives. However, none has assessed the risk in women using subcutaneous hormonal implants. A recent study reported a 48% higher risk of venous thrombosis in women using a vaginal ring compared with those using combined oral contraceptives containing levonorgestrel, and a few studies have reported the risk in women using a transdermal combined contraceptive patch, although the results were conflicting.
Using a historical national registry based cohort study design, we assessed the absolute and relative risk of venous thrombosis in Danish women using non-oral hormonal contraception.