my wife is 23 weeks pregnant.....done her usg as per doctors advice....usg reports shows lower edge of placenta and the external os distance is 2.6 cm, placenta maturity grade is 1. At the time of usg, the doctor who had done the usg said there is no problem, it is normal and there will be no problem in case of flight travel. But when i consulted the doctor who asked for the usg said clearly no travel through flight. Now i want to know actual situation is what and whether we can take flight travel for 3 hours( break journey of 1 hr and 2 hr). What is the actual reference range of distance between lower edge of placenta and external os?