Hi, most airlines will let you fly up to 34 weeks, some even 36 with a doctors certificate stating you are well enough to fly. The best thing you can do is to phone the airline which you are flying with and check their policy, or get the travel agents to do it for you. I do know some airlines can be quite funny over this matter and will not let you fly after 32 weeks, so plz contact them directly.
I have had the same problem - we are due to emigrate to Mauritius in August / September and we have had to check with Air Mauritius the lastest I can fly.
Hope this helps Sarah x