If your pregnancy is healthy (uterus size is on target with dates, no bleeding or placental abnormalities on ultrasound, a singleton pregnancy, etc), you should be fine until starting to get close to the due date (where do you want to have your baby, at home or in another city? Or, worse yet, do you want to go into labor on the plane?) Still, it's best to check with your doctor before you buy a ticket. The middle trimester is often the best for comfort during flying. (You're less tired and sick than the first trimester, and you're smaller than the third trimester, when long sitting can really make your legs swell and hurt, as well as increase the risk of clots slightly. **Walk often!!** Think about compression stockings.)

>Your health care provider might caution against air travel if your pregnancy is considered high risk or you're at risk of preterm labor. Similarly, your health care provider might restrict travel of any type after 36 weeks of pregnancy.

The Mayo Clinic gives these additional tips:

>- Check the airline's policy about air travel during pregnancy. Guidelines for pregnant women might vary by carrier and destination.
>- Choose your seat carefully. For the most space and comfort, consider requesting an aisle seat. (Some seats in front of the cabin have even more space.)
>- Promote circulation. If possible, take occasional walks up and down the aisle. If you must remain seated, flex and extend your ankles often. (This is a must the further on you are.)
>- Drink plenty of fluids. Low humidity in the cabin can lead to dehydration.
>- Decreased air pressure during flight can slightly reduce the amount of oxygen in your blood, but this doesn't pose risks if you're otherwise healthy.

If you must fly frequently during your pregnancy, discuss the risks of increased radiation during high-altitude flights with your doctor. He or she might limit your total flight time during pregnancy.

If you're flying during your third trimester, it's probably wise to bring a copy of your prenatal chart just in case, with your due date, pregnancy-related lab tests and ultrasounds, past obstetric, medical and surgical history, and a flow sheet of vital signs taken at each visit. 

<sub>[Is it safe to fly during pregnancy? (Mayo Clinic)](http://www.mayoclinic.org/healthy-living/pregnancy-week-by-week/expert-answers/air-travel-during-pregnancy/faq-20058087)</sub>  
<sub>[Is it safe to fly while pregnant? (NHS.UK)](http://www.nhs.uk/chq/Pages/927.aspx?CategoryID=54#close)</sub>  
<sub>[Air Travel During Pregnancy (ACOG)](http://www.acog.org/Resources-And-Publications/Committee-Opinions/Committee-on-Obstetric-Practice/Air-Travel-During-Pregnancy)</sub>