When I have my second baby, I took a tour when my baby was about 10-12 weeks. On the first day, its oK. But on mid of the second day, I found some blood on my pant during lunch. I quited the tour and spend some money to fly back to HK. It was so lucky that the baby was no problem. But I worried about her for a long long time and I really regret that I have made such a rash decision to take a tour on the initial stage of my pregnancy.
I don't know whether the baby is affected by air pressure in the plane. But I think a pregnant woman will be very tired even you take a tour because you need to walk a lot more.
I think if you just go to a resort and do not need to travel around to different sight seeing points, I think that will be fine. But if you take a tour, you should choose a tour with relax schedule.