When i was 3 months i went to Egypt, flying was fine but ya get a strange feeling as ya get the butterflies when going up and down but nout to worry about, it's perfectly fine to fly while pregnant
I flew 8 hours at 16 weeks and it was fine. As huni saiid your wife should walk around and keep hydrated. Enjoy your holiday.
I'm 18 weeks prego tomorrow and this weekend I'll be flying for the 3rd time. I've also travelled long distance by train and bus recently.
its not a problem, if you're not a high risk pregnancy and ur doc approved. ur wife can wear stockings if she's worried about air craft pressure affecting her blood circulation. also carry some hand sanitizers as there's lots she'll be touching while travelling. and make sure to get up and walk around a bit during the flight, instead of sitting for 4 hours straight. drink lots of water to avoid dehydration. and dont forget to carry the prenatal vitamins!
she'll be just fine :-)
happy flying !!