Air travel during pregnancy and the risk of venous thrombosis

BACKGROUND Pregnancy and air travel independently increase the risk of venous thrombosis. However, there is a lack of data regarding the added risk, if at all, of thrombosis after air travel during pregnancy. OBJECTIVE This study aimed to determine the potential added risk of venous thromboembolism among pregnant women who traveled by air. STUDY DESIGN This was an observational retrospective study using data from 452,663 live births between the years 2010 to 2019. The study group consisted of women who flew during pregnancy. Data of pregnant women who flew during pregnancy were compared with that of pregnant women who did not fly during pregnancy. The primary outcome was venous thromboembolism during pregnancy and in the postpartum period. A case of venous thromboembolism was deemed related to air travel only if it occurred up to 8 weeks after the return flight (exposure time). Propensity score weighting Poisson regression was calculated to assess the effect and to control selection biases. Risk per day was calculated. RESULTS Overall, 421,125 live births were included. Of those cases, 33,674 (8%) had traveled by air during pregnancy (study group), and 387,451 (92%) did not (control group). There were 6 cases of venous thromboembolism after a flight that occurred during the exposure time of 8 weeks and 285 cases of venous thromboembolism in the control group (0.05% vs 0.07%; P=.158). When the propensity weighting Poisson regression was calculated as risk per day, there was a significantly increased risk between the study and control groups (0.00031% vs 0.00022%; hazard ratio, 1.406; P=.005). CONCLUSION The overall risk of venous thromboembolism after air travel is low; however, our study found that the risk of venous thromboembolism during pregnancy is increased by air traveling.