best trimester, which month, to air travel for a pregnant lady?

what are the risks

The fourth or fifth month seem to be the easiest for most women to travel, whether by air or land, but the risks are different for each woman, and each pregnancy. You should just discuss it with your (her?) doctor.

Honestly, I am not completely sure what all of the risks are, but you should really seek the advice of your doctor. If you are having a moderate to high risk pregnancy...the risks could vary alot.
Most women are advised to not travel in their last trimester...especially the last few weeks!
Congratulations!!!

In a low risk pregnancy, most airlines allow you to fly up to 32-35 weeks. As far as when before then, well the best time would be when you feel the best!!! If trying to plan ahead, probably the 2nd trimester. If you're morning sick, you'll more than likely be over it by then, and won't be so far along that sitting, walking and standing in line are totally miserable. Do be sure to stay hydrated, take a water bottle on the plane. Also get up to move around at least once an hour (if you stay hydrated like you should, the trips to the airplane bathroom will likely take care of this.)