Background: Cesarean sections (CS) are believed to be associated with greater risks of postpartum VTE. Our objective was to systematically review the evidence on this association and on the absolute risk of VTE following CS.

Methods: We searched PubMed, Embase, and conference proceedings from 1980 to November 2015 for reports on the associations of delivery methods with postpartum VTE and on the incidence of VTE following CS. Studies on thrombophilia or recurrent VTE were excluded, and the search was restricted to prospective studies when assessing the incidence of VTE. Pooled relative and absolute risks were estimated with random effects models.

Results: The search retrieved 28 mostly retrospective observational studies comparing risks of VTE following CS and following vaginal deliveries (VD) (> 53,000 VTE events) and 32 prospective studies reporting risks of VTE following CS (218 VTE events). Compared with VD, the relative risk of VTE following CS ranged from 1 to 22, with a meta-analytic OR of 3.7 (95% CI, 3.0-4.6). Adjustment for age and BMI had a marginal influence on the estimated pooled OR. Associations were observed for both elective and emergency CS, with stronger estimates of associations for emergency CS. The pooled incidence was 2.6 VTE per 1,000 CS (95% CI, 1.7-3.5) and was greater in studies with a longer and better follow-up in the postpartum period (4.3 per 1,000 CS).

Conclusions: The risk of VTE was fourfold greater following CS than following VD; seemed independent of other VTE risk factors; and was greater following emergency CS than following elective CS. On average, three in 1,000 women will develop a VTE following CS.