I would still talk to your OB/GYN before you confirm your flights. Or at least purchase vacation insurance since you will not be able to predict how the end of your pregnancy will go. I've had preterm labor with one, pregnancy-induced-hypertension with my second, and an entirely uneventful pregnancy with my third.
From Ask the Experts (By Ann Linden, Certified Nurse-Midwife)
Question: My family has planned a trip to Florida when I'll be around seven months pregnant. Is it safe to fly this late in pregnancy?
Answer: While 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 midwife or doctor before you book your flight. If you have medical or obstetric complications such as diabetes or high blood pressure, are carrying twins, have placental abnormalities or a history of blood clotting disorder, or are at risk for preterm labor, your healthcare provider will probably advise you to stay close to home throughout your pregnancy. (Well-controlled mild gestational diabetes shouldn't be a problem.)
Even if you're enjoying an uncomplicated pregnancy, it's prudent 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 midwife or doctor stating your expected due date to avoid disputes at the boarding gate. Each airline, however, has different rules about when and if it will allow you to fly. Check our Airline policies for pregnant travelers chart for more information. 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 copy of your medical history, which should include your due date, risk factors, and blood type, any medications you're currently taking, and any that you're allergic to as well. See our Emergency contact sheet for pregnant travelers for a complete list of names, phone numbers, and information you should have with you when you travel.
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. It's also recommended to 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. Support hose help with swelling, too.
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 many 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.