I have flown frequently while pregnant, both this time and when I was pregnant with Connor. I have been lucky to have had relatively easy pregnancies (other than the constant nausea) and I consulted my doctor to make sure my planned trips were ok. I have now "passed" the recommended flying stage (or the stage when there is a greater chance that you will deliver in the air!) so next time I travel it will be with two children!
My tips for air travel while pregnant include speaking with your doctor before booking. It's prudent to discuss your trip with your doctor in advance and It's wise to have a doctor's note in case you are asked what how far along you are.
You never know what's going to happen when you are pregnant, so book travel insurance for your flight. If you have to cancel then at least you won't lose everything.
Wear comfortable clothing (and shoes!) and dress in layers. Sometimes the plane can be warm and sometimes it can be cool, it's best to be prepared for both cases.
Drink lots of water to stay hydrated.
Stretch in your seat and go for a walk in the aisle often. (if you are drinking a lot of water this may help force you out of your seat for a trip to the washroom!)
Because you are pregnant doesn't mean you have to stop going places....