Associate Professor Frank Firkin and Associate Professor Harshal Nandurkar, authors of the article, comment:
Increased levels of oestrogen are associated with increased thromboembolic risk during long-haul flights, as discussed in our article, and it is natural to consider this to apply to pregnancy.
It is, however, fundamental that guidance on managing risk factors be based on published evidence or consensus that can reasonably be accessed. In the case of pregnancy there are major publications that do not support an unequivocal assertion of an association with pregnancy in general.
In an article describing life-threatening venous thromboembolism manifested by pulmonary embolism after long-haul flights, there were no cases in pregnant women in contrast to a number of cases in women taking oral oestrogens.1In addition, the most recent American College of Obstetricians and Gynecologists Committee Opinion states there is a lack of evidence of increased venous thromboembolism risk in pregnant women.2