I have the same situation as well. My wife is 20 weeks pregnant now and I had done some research into this a few months ago. Most airlines have rules about not allowing pregnant women board an aircraft after a certain time into the pregnancy. But she can get around this by either having a doctor certify that she is fit to fly and/or having a medical exam from the airlines medical staff.

Either way, I strongly advise calling up the airline and asking them what to do. No sense getting a IDB when you could have been prepared beforehand.

BTW, I fly EWR-PEK back and forth about once a month. I'll make a mental note to keep my eye out for a pregnant couple when I travel in Dec and Jan.

Good Luck.