I usually travel lots and lots and have no problems whatsoever flying.
I HATE flying when pregnant. I had no idea how crap I was going to feel- first pregnancy here. I've done six flights so far in my pregnancy (23 weeks with twins) and have said enough's enough- no WAY am I stepping on a plane again until my children are on the outside, not the inside, of me! Flying makes me feel terrible. Two of the flights were 7 hours each in economy class which normally I would do without blinking but each one felt like an eternity.
The cabin pressure makes my insides (and their occupants) feel terrible- gassy, windy, achey, uncomfortable. Have you ever seen what flying does to a plastic bottle- where the pressure makes it shrivel up or blow out? Well, that's your insides. And the occupants REALLY don't like it!
Sitting in one position for so long makes my back and bum really painful. Wanting to pee all the time with the cabin pressure and an already stressed bladder is torture. I've had two weeping fits on planes now, as a result of being pregnant, uncomfortable, achey, claustrophobic and fed up. (And if you knew just what a fantastically intrepid traveller I am normally you'd be aghast.)
It might be marginally better in business class but the cabin pressure issue is still the same. And unless it's proper swanky business class like Emirates or Singapore Airlines you can't lie flat anyway.
I've mentioned it to a couple of pregnant friends and we have all had the same experience, and we're all amazed that nobody ever tells you how horrid flying while pregnant is!
In fairness, it doesn't do any damage at all to the baby. It's perfectly safe. Just really uncomfortable.