if you have a healthy pregnancy, it is fine to travel .. i travelled a total of 17 hours flight when i was 19weeks pregnant and will have another flight back home (i live overseas) when im 30 weeks .. since ill be more than 28 weeks, i will have to see and get a letter safe to fly from my gynae .. but she mentioned as long if baby is okay, pregnancy is fine it should be okay .. best to consult your gynae if have doubts :)
It is prudent to ask the Gynae before travelling.