title: Pre-pregnancy BMI, delivery BMI, gestational weight gain and the risk of postpartum venous thrombosis.
abstract: OBJECTIVE
  To characterize the risk of postpartum venous thromboembolism (VTE) associated with body-mass-index (BMI) in both pre-pregnancy and at delivery, and with gestational weight gain (GWG).
  
  
  METHODS
  In a population-based, case-control study, we identified all women in Washington State with ICD-9 codes for VTE in the postpartum period between 2003 and 2011. Controls were women without VTE in the postpartum period, matched by delivery year to cases. Pre-pregnancy BMI, delivery BMI, and covariates were abstracted from birth certificates. Adjusted logistic regression models separately estimated postpartum VTE risk associated with categories of BMI in pre-pregnancy and at delivery.
  
  
  RESULTS
  Cases (n=289) had a higher mean BMI than controls (n=4208) pre-pregnancy (29.9kg/m(2) and 26.3kg/m(2), respectively) and at delivery (34.8kg/m(2) vs. 31.4kg/m(2), respectively), with similar gestational weight gains. Compared with women with a normal pre-pregnancy BMI (18.5-24.9kg/m(2)), overweight (BMI 25-29.9kg/m(2)) and obese (BMI≥30kg/m(2)) women were at a 1.5-fold and 1.8-4 fold greater risk of postpartum VTE, respectively, with greatest risks in women with class III obesity (BMI≥40kg/m(2): OR 4.0, 95%CI 2.7-6.3). Observed associations of delivery BMI with postpartum VTE were less strong than those of pre-pregnancy BMI. Large weight gains during pregnancy (>22kg) also contributed to greater VTE risks (OR 1.5, 95%CI 1.0-2.2).
  
  
  CONCLUSIONS
  Maternal BMI is an important risk factor for postpartum VTE, grading from weak in overweight women to very strong in women with class III obesity. Care providers may prefer to use pre-pregnancy BMI, along gestational weight gain, when stratifying the risk of postpartum VTE at delivery.
authors.affiliation: Division of Angiology and Haemostasis, Geneva University Hospitals and Faculty of Medicine, Geneva, Switzerland; Department of Epidemiology, University of Washington, Seattle, USA. Electronic address: marc.blondon@hcuge.ch.
authors.forename: M
authors.initials: M
authors.lastname: Blondon
authors.affiliation: Department of Epidemiology, University of Washington, Seattle, USA; Department of Nutrition, Harvard T.H. Chan School of Public Health, Boston, USA.
authors.forename: L B
authors.initials: LB
authors.lastname: Harrington
authors.affiliation: Division of Angiology and Haemostasis, Geneva University Hospitals and Faculty of Medicine, Geneva, Switzerland.
authors.forename: F
authors.initials: F
authors.lastname: Boehlen
authors.affiliation: Division of Angiology and Haemostasis, Geneva University Hospitals and Faculty of Medicine, Geneva, Switzerland.
authors.forename: H
authors.initials: H
authors.lastname: Robert-Ebadi
authors.affiliation: Division of Angiology and Haemostasis, Geneva University Hospitals and Faculty of Medicine, Geneva, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Righini
authors.affiliation: Department of Epidemiology, University of Washington, Seattle, USA; Group Health Research Institute, Group Health Cooperative, Seattle, USA; Seattle Epidemiologic Research and Information Center, Department of Veterans Affairs Office of Research and Development, Seattle, USA.
authors.forename: N L
authors.initials: NL
authors.lastname: Smith
mesh_terms: D015992:Body Mass Index; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D049590:Postpartum Period; D011247:Pregnancy; D011249:Pregnancy Complications, Cardiovascular; D012307:Risk Factors; D020246:Venous Thrombosis / Q000209:etiology*; D015430:Weight Gain