As per airlines website -
All airlines make up their own rules and regulations regarding pregnant women. Some do not restrict travel at all, no matter what stage of pregnancy a women is in, and others start to restrict at 7 months, although the majority restrict around 36 weeks.
While traveling I advise you to keep your medical records, and the name and number of your doctor. You should also get the name and number of a doctor where you will be staying/visiting in case an emergency comes up.