I checked with my doc before i flew at 32 plus weeks and he said there were no issues (i had no BP problems or fluid problems or anything)with flying if you had a normal pregnancy. I had a scare while I was away (a very small bleed and a few contractions that they couldn't find what it was) when I asked should I fly home or drive - they said that they would even recommend I flew becuase I'd be at my destination faster and I'd be much more comfortable than sitting in a car for hours - the flight itself wasn't likely to do anything and if I did start having contractions I'd be at medical assistance within the hour anyway.

I'm pretty sure a couple of docs have told me that the only reason they don't want you flying late in pregancny (and these days I'm sure its post 36 weeks and for some airlines there is no deadline) is cuase they jsut don't want you going into labour on the flight (cause you are nearing that time of the pregnancy when it could happen anytime) and having to deal with a "medical emergency" in flight.