Thrombotic risk during pregnancy: a population study.
OBJECTIVE: To determine the incidence of pregnancy-related venous thromboembolic events and the relationship to selected risk factors such as maternal age, parity, smoking, preeclampsia, or cesarean delivery. METHODS: All Swedish women reported as having pregnancy-related venous thromboembolic events during 1990-1993 (608 of 479,422 deliveries) were compared with all thrombosis-free Swedish pregnant women during 1993 (114,940). RESULTS: The incidence of pregnancy-related venous thromboembolic events was 13 per 10,000 deliveries. Cesarean delivery was associated with a fivefold increased risk of venous thromboembolic events. Advanced age was not a significant risk factor itself, but was associated with an age-related increase in frequency of cesareans. Women with preeclampsia were at a threefold higher risk postpartum, but at no increased risk before delivery. There was a tobacco consumption-dependent increase in the risk of thrombosis among smokers. CONCLUSION: The incidence of pregnancy-related thrombosis was 13 per 10,000 and provided new insights to important risk factors such as age, cesarean delivery, smoking, and preeclampsia.