Research suggests that occasional air travel is considered safe for pregnant women, with most commercial airlines allowing pregnant women to fly up to the 36th week of pregnancy. The restriction after week 36 is mainly there in case you go into early labor, as access to medical services is obviously limited on a plane.
These guidelines apply to a healthy, normal pregnancy, so if you are planning a flight be sure to consult your doctor. It’s also worth considering the duration of the flight. Flights longer than 4 hours are associated with an increased risk of lower extremity edema and venous thrombotic events. As a preventative measure, elastic compression stockings are recommended for medium to long-haul flights. Also keep in mind that turbulence is unpredictable, so always use a seat belt when seated to prevent trauma.