Although it can be perfectly safe to fly during much of your third trimester (up to 36 weeks), be sure to discuss your trip plans with your healthcare provider before you book your flight. In certain high-risk cases, your healthcare provider may advise you to stay close to home throughout your pregnancy. If you're carrying twins or multiples, have diabetes or high blood pressure, have placental abnormalities or vaginal bleeding, are under observation for preterm labor, or have a history of forming blood clots (including prior to pregnancy), the smart choice may be to postpone your travels.
Even if you're enjoying an uncomplicated pregnancy, it's best to avoid flying during your final month, when you're more likely to go into labor. Many airlines, in fact, won't let women on board who are due to deliver within seven or sometimes 30 days of the flight (they don't want you to deliver while in the air!). Be sure to carry a note from your healthcare provider stating your expected due date to avoid disputes at the boarding gate. However, each airline has different rules about when and whether it will allow you to fly. And don't forget to take into account how far along you'll be on the return flight.
Before you leave, have your healthcare provider refer you to a midwife or obstetrician at your destination in case you need medical attention during your vacation. Carry a complete list of emergency contacts and, if you're in your second or third trimester, carry a copy of your prenatal chart as well. A prenatal chart should include your age, due date, last menstrual period, number and outcomes of prior pregnancies, risk factors for disease, pregnancy-related lab tests and ultrasounds, medical and surgical history, and a flow sheet of vital signs taken at each visit.
If you're healthy and have no obstetric problems, you and your baby should have no trouble in the pressurized cabin of a commercial airliner. The best thing to do is to make yourself as comfortable as you can during the flight. Request a seat in the middle of the plane over the wing for the smoothest ride, or a bulkhead seat for more legroom.
In either case, reserve a seat on the aisle so you can get to the bathroom easily and get up to walk and stretch. Pregnant women who are immobile for long periods of time are at increased risk for developing blood clots, so be sure to walk around the cabin at least once an hour. You should also stretch and flex your feet and legs in your seat every 30 minutes. Wearing maternity support panty hose (not knee highs) helps keep the blood moving in your legs and decreases your risk for clots and swollen feet.
When seated, keep your seatbelt fastened under your belly and low on your hips at all times. Also, drink plenty of fluids, especially water, to stave off the dehydrating effects of dry cabin air. Caffeine acts as a diuretic, so it's best to avoid coffee, tea, and caffeinated soft drinks before and during the flight. And beware of gas-producing meals or drinks before takeoff. The trapped gas from foods such as cabbage and beans expands at higher altitude, making for an uncomfortable trip.