title: Venous thrombosis in users of non-oral hormonal contraception: follow-up study, Denmark 2001-10.
abstract: OBJECTIVE
  To assess the risk of venous thrombosis in current users of non-oral hormonal contraception.
  
  
  METHODS
  Historical national registry based cohort study.
  
  
  METHODS
  Four national registries in Denmark.
  
  
  METHODS
  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.
  
  
  METHODS
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Gynaecological Clinic, Copehagen Ø, Juliane Marie Centre, Rigshospitalet, University of Copenhagen, Denmark. lidegaard@rh.regionh.dk
authors.forename: Ojvind
authors.initials: O
authors.lastname: Lidegaard
authors.forename: Lars Hougaard
authors.initials: LH
authors.lastname: Nielsen
authors.forename: Charlotte Wessel
authors.initials: CW
authors.lastname: Skovlund
authors.forename: Ellen
authors.initials: E
authors.lastname: Løkkegaard
mesh_terms: D000293:Adolescent; D000328:Adult; D000925:Anticoagulants / Q000627:therapeutic use; D003271:Contraceptive Agents, Female / Q000008:administration & dosage / Q000009:adverse effects / Q000627:therapeutic use*; D003274:Contraceptive Devices, Female / Q000009:adverse effects / Q000706:statistics & numerical data*; D003277:Contraceptives, Oral, Combined / Q000009:adverse effects / Q000627:therapeutic use; D003278:Contraceptives, Oral, Hormonal / Q000009:adverse effects / Q000627:therapeutic use; D003718:Denmark / Q000453:epidemiology; D004343:Drug Implants; D004812:Epidemiologic Methods; D005260:Female; D006801:Humans; D016912:Levonorgestrel / Q000009:adverse effects / Q000627:therapeutic use; D008875:Middle Aged; D009644:Norgestrel / Q000009:adverse effects / Q000031:analogs & derivatives / Q000627:therapeutic use; D057968:Transdermal Patch; D020246:Venous Thrombosis / Q000139:chemically induced / Q000453:epidemiology*; D055815:Young Adult
chemical_list: D000925:Anticoagulants; D003271:Contraceptive Agents, Female; D003277:Contraceptives, Oral, Combined; D003278:Contraceptives, Oral, Hormonal; D004343:Drug Implants; D009644:Norgestrel; D016912:Levonorgestrel; C017576:norgestimate