Hello,
I took the plane to come here from France on my 28 weeks, so I will say that there is no problem. Of course, I saw my doctor just before (2 days before) so he could tell me if everything was Ok or not.
I was in the business class thanks to my husband company, so I had plenty of places to stretch my legs. If you don't have this chance, you should try and walk from time to time.
And of course, don't forget to drink a lot !!!
Have a nice trip !