title: Incidence and risk factors of venous thromboembolism during postpartum period: a population-based cohort-study.
abstract: BACKGROUND
  The awareness of the incidence and timing of postpartum venous thromboembolic events guides the use of thromboprophylaxis. Our aims were to assess the incidence and mortality of venous thromboembolic events and identify its associated risk factors during different postpartum periods.
  
  
  METHODS
  A population-based controlled cohort study by combining four large registers in 2001-2011. All women with a recent delivery were identified. The incidence, risk factors and mortality of venous thromboembolic events 0-180 days after delivery were assessed by using all healthy delivered women as the control group. The incidence was compared with that of the nonpregnant women.
  
  
  RESULTS
  Among the 634 292 delivered women, 1169 had venous thromboembolic events 0-180 days postpartum. The incidence of venous thromboembolic events was highest during the first week postpartum: 37-fold compared with nonpregnant women, declining to two-fold immediately after that. Almost half of the venous thromboembolic events occurred between 43 and 180 days postpartum. The incidence of venous thromboembolic events was four-fold compared with that of nonpregnant women. Three venous thromboembolic events-related deaths occurred. Older age, higher body mass index, thrombophilia, multiple pregnancy, gestational diabetes, anemia, chorioamnionitis, threatening premature birth, in vitro fertilization with ovarian hyperstimulation, primiparity, cesarean section, cardiac/renal diseases, and varicose veins were associated with an increased risk for postpartum venous thromboembolic events. The risk remained elevated for 180 days in women with thrombophilia, cesarean section, multiple pregnancy, varicose veins, and cardiac disease.
  
  
  CONCLUSIONS
  The risk of venous thromboembolic events remained elevated compared with that of the nonpregnant women after the usually defined postpartum period (6 weeks). The results might assist in selecting women in need of thromboprophylaxis.
authors.affiliation: Department of Obstetrics and Gynecology, Helsinki University Hospital, University of Helsinki, Helsinki, Finland.
authors.forename: Päivi J
authors.identifier: http://orcid.org/0000-0002-9631-8608
authors.initials: PJ
authors.lastname: Galambosi
authors.affiliation: Information Services Department, THL National Institute for Health and Welfare, Helsinki, Finland.|Research Center for Child Psychiatry, University of Turku, Turku, Finland.|Department of Neurobiology, Care Sciences and Society, Division of Family Medicine, Karolinska Institute, Stockholm, Sweden.
authors.forename: Mika
authors.identifier: http://orcid.org/0000-0001-8254-7525
authors.initials: M
authors.lastname: Gissler
authors.affiliation: University of Turku and Turku University Hospital, Turku, Finland.
authors.forename: Risto J
authors.initials: RJ
authors.lastname: Kaaja
authors.affiliation: Department of Obstetrics and Gynecology, Helsinki University Hospital, University of Helsinki, Helsinki, Finland.
authors.forename: Veli-Matti
authors.identifier: http://orcid.org/0000-0002-5235-1668
authors.initials: VM
authors.lastname: Ulander
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D015331:Cohort Studies; D005260:Female; D005387:Finland / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D011247:Pregnancy; D011250:Pregnancy Complications, Hematologic / Q000453:epidemiology* / Q000209:etiology; D011644:Puerperal Disorders / Q000453:epidemiology* / Q000209:etiology; D012307:Risk Factors; D054556:Venous Thromboembolism / Q000453:epidemiology* / Q000209:etiology; D055815:Young Adult
keywords: Incidence; low-molecular-weight heparin; postpartum; register; risk factor; thromboprophylaxis; venous thromboembolic event