title: Defining venous thromboembolism and measuring its incidence using Swedish health registries: a nationwide pregnancy cohort study.
abstract: OBJECTIVE
  To accurately define venous thromboembolism (VTE) in the routinely collected Swedish health registers and quantify its incidence in and around pregnancy.
  
  
  METHODS
  Cohort study using data from the Swedish Medical Birth Registry (MBR) linked to the National Patient Registry (NPR) and the Swedish Prescribed Drug Register (PDR).
  
  
  METHODS
  Secondary care centres, Sweden.
  
  
  METHODS
  509,198 women aged 15-44 years who had one or more pregnancies resulting in a live birth or stillbirth between 2005 and 2011.
  
  
  METHODS
  To estimate the incidence rate (IR) of VTE in and around pregnancy using various VTE definitions allowing direct comparison with other countries.
  
  
  RESULTS
  The rate of VTE varied based on the VTE definition. We found that 43% of cases first recorded as outpatient were not accompanied by anticoagulant prescriptions, whereas this proportion was much lower than those cases first recorded in the inpatient register (9%). Using our most inclusive VTE definition, we observed higher rates of VTE compared with previously published data using similar methodology. These reduced by 31% (IR=142/100,000 person-years; 95% CI 132 to 153) and 22% (IR=331/100,000 person-years; 95% CI 304 to 361) during the antepartum and postpartum periods, respectively, using a restrictive VTE definition that required anticoagulant prescriptions associated with diagnosis, which were more in line with the existing literature.
  
  
  CONCLUSIONS
  We found that including VTE codes without treatment confirmation risks the inclusion of false-positive cases. When defining VTE using the NPR, anticoagulant prescription information should therefore be considered particularly for cases recorded in an outpatient setting.
authors.affiliation: Division of Epidemiology and Public Health, University of Nottingham, Nottingham, UK Department of Medical Epidemiology and Biostatistics, Karolinska Institute, Stockholm, Sweden Nottingham Digestive Diseases Biomedical Research Unit, University of Nottingham, Queens Medical Center, UK.
authors.forename: Alyshah
authors.initials: A
authors.lastname: Abdul Sultan
authors.affiliation: Division of Epidemiology and Public Health, University of Nottingham, Nottingham, UK.
authors.forename: Joe
authors.identifier: http://orcid.org/0000-0002-1135-9356
authors.initials: J
authors.lastname: West
authors.affiliation: Department of Medicine, Clinical Epidemiology Unit, Karolinska Institutet, Stockholm, Sweden Department of Women's and Children's Health, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Olof
authors.initials: O
authors.lastname: Stephansson
authors.affiliation: Division of Epidemiology and Public Health, University of Nottingham, Nottingham, UK.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Grainge
authors.affiliation: Division of Epidemiology and Public Health, University of Nottingham, Nottingham, UK.
authors.forename: Laila J
authors.initials: LJ
authors.lastname: Tata
authors.affiliation: Division of Epidemiology and Public Health, University of Nottingham, Nottingham, UK.
authors.forename: Kate M
authors.initials: KM
authors.lastname: Fleming
authors.affiliation: Division of Epidemiology and Public Health, University of Nottingham, Nottingham, UK.
authors.forename: David
authors.initials: D
authors.lastname: Humes
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institute, Stockholm, Sweden Department of Paediatrics, Örebro University Hospital, Örebro, Sweden.
authors.forename: Jonas F
authors.initials: JF
authors.lastname: Ludvigsson
mesh_terms: D000328:Adult; D015331:Cohort Studies; D005260:Female; D006801:Humans; D015994:Incidence; D011247:Pregnancy; D011250:Pregnancy Complications, Hematologic / Q000175:diagnosis / Q000453:epidemiology*; D012042:Registries; D012307:Risk Factors; D063127:Secondary Health Care; D013548:Sweden / Q000453:epidemiology; D054556:Venous Thromboembolism / Q000175:diagnosis / Q000453:epidemiology*; D055815:Young Adult
keywords: HAEMATOLOGY; OBSTETRICS