It does depend on the airline, you'll have to call them up to find out exactly. But yes most of them are ok up to 30 weeks. If it's after that, it's still possible but you'll need a clearance from your doctor saying that it's not very likely she'll go into labor in the next couple of days. The doctor clearance has to be done a day or two before flying. I would do it sooner rather than later. Think about how uncomfortable airplane seats are. Now add 30 weeks of pregnancy? No thank you, haha