Defining venous thromboembolism and measuring its incidence using Swedish health registries: a nationwide pregnancy cohort study

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Abdul Sultan, Alyshah ; West, Joe ; Stephansson, Olof ; Grainge, Matthew J ; Tata, Laila J ; Fleming, Kate M ; Humes, David ; Ludvigsson, Jonas F (2015)
  • Publisher: BMJ Publishing Group
  • Journal: BMJ Open, volume 5, issue 11 (eissn: 2044-6055)
  • Related identifiers: doi: 10.1136/bmjopen-2015-008864, pmc: PMC4654387
  • Subject: RG | Obstetrics and Gynaecology | HAEMATOLOGY | OBSTETRICS | 1506 | Research | 1845
    mesheuropmc: equipment and supplies | cardiovascular diseases

Objective: To accurately define venous thromboembolism (VTE) in the routinely collected Swedish health registers and quantify its incidence in and around pregnancy.\ud Study design: 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).\ud Setting: Secondary care centres, Sweden.\ud Participant: 509 198 women aged 15–44 years who had one or more pregnancies resulting in a live birth or stillbirth between 2005 and 2011.\ud Main outcome measure: To estimate the incidence rate (IR) of VTE in and around pregnancy using various VTE definitions allowing direct comparison with other countries.\ud 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.\ud 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.
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