Risk of venous thromboembolism during the postpartum period: a systematic review.

OBJECTIVE: To determine, from the literature, the risk of venous thromboembolism during the postpartum period.

DATA SOURCES: We searched PubMed and Cochrane Library databases for all articles (in all languages) published in peer-reviewed journals from database inception through May 2010 for evidence related to incidence of venous thromboembolism in postpartum women.

METHODS OF STUDY SELECTION: We included studies reporting relative risk, incidence rate, or cumulative incidence of venous thromboembolism in postpartum women.

TABULATION, INTEGRATION, AND RESULTS: We included 15 articles reporting findings from 13 studies. Two studies directly comparing venous thromboembolism during the first 6 weeks postpartum to nonpregnant, nonpostpartum women reported relative effect measures of 21.5 (rate ratio; 95% confidence interval [CI] unable to be calculated) and 84 (odds ratio; 95% CI 31.7-222.6), respectively. A third study reported relative effect measures for deep venous thrombosis (15.2, 95% CI 13.2-17.6; standardized incidence ratio) and pulmonary embolism (9.2, 95% CI 6.5-12.7) separately. Three studies reported incidence rates of venous thromboembolism during the postpartum period (range 25-99 per 10,000 woman-years). We compared these incidence rates to baseline rates among nonpregnant, nonpostpartum women reported in the literature to generate rate ratios; these rate ratios ranged from 2.5 to 21.5. Nine studies reported cumulative incidence proportions of postpartum venous thromboembolism, ranging from 0.14 to 3.24 per 1,000 deliveries at 6 weeks postpartum. Incidence of venous thromboembolism was highest immediately after delivery (standardized incidence ratio for deep venous thrombosis 115.1 [95% CI 96.4-137.0], and for pulmonary embolism 80.7 [95% CI 53.9-117.9]); between 4 and 6 weeks postpartum, risk declined but was still approximately five-times to seven-times that of nonpregnant, nonpostpartum women.

CONCLUSION: During the first 6 weeks postpartum, women's risk of venous thromboembolism increased 21.5-fold to 84-fold from baseline in nonpregnant, nonpostpartum women in studies that included an internal reference group. Although incidence of venous thromboembolism declined quickly after delivery, when this risk returns to baseline is not clear from current data.