Anecdotally, there have been reports of patients complaining that their menstrual periods get worse when they fly. But there haven’t been any scientific articles documenting this as a common occurrence among menstruating women. One theory is that prolonged sitting causes blood to pool in the lower half of the body and this decreased venous blood return to the heart can increase menstrual bleeding. Blood clotting usually is not affected by the altitude on plane flights because the cabin is pressurized. Unfortunately aside from more absorbent pads or tampons, there isn’t much to do about increased menstrual bleeding on plane flights.