Epidemiology of pregnancy-associated venous thromboembolism: a population-based study in Canada.

OBJECTIVE: To estimate the frequency of, and to identify risk factors for, pregnancy-associated venous thromboembolism (VTE), including deep vein thrombosis (DVT) and pulmonary embolism (PE) requiring hospitalization.

METHODS: We conducted a population-based cohort study (N = 3 852 569) using the Discharge Abstract Database of the Canadian Institute for Health Information (CIHI), for the fiscal years 1991-1992 to 2005-2006. All women with pregnancy-related hospitalizations in Canada (excluding Quebec and Manitoba) were identified. DVT and PE rates were calculated using the number of hospital deliveries (i.e., cohort of women at risk) as the denominator for the antepartum and peripartum (labour and delivery) hospitalizations and for postpartum readmissions. Risk factors for DVT/PE were identified using logistic regression.

RESULTS: During the antepartum, peripartum, and postpartum periods, 5.4, 7.2, and 4.3 VTE cases per 10,000 pregnancies, respectively were observed. The total incidence of DVT was 12.1 per 10,000 pregnancies (0.26 deaths per 100,000), and the rate for PE was 5.4 per 10,000 (0.96 deaths per 100,000). The strongest risk factors for DVT occurrence during the peripartum period were thrombophilia (adjusted odds ratio [aOR] 15.4; 95% CI 10.8-22.0), a past history of circulatory disease, and major puerperal infection, whereas those for PE were previous DVT (aOR 56.9; 95% CI 40.9-79.1), heart disease (aOR 43.4, 95% CI 35.0-53.9), antiphospholipid syndrome, past history of circulatory disease, transfusion, and major puerperal infection.

CONCLUSION: Cases of VTE and associated deaths occur most frequently during the peripartum period. Although mortality from pregnancy-associated VTE is low, maternal characteristics and other factors can be used to identify women at risk for VTE.