It's very common, mainly in Hawaii, I believe, and the Chinese are running a lot of it. Heavily pregnant women go to America on "holiday" and "just happen" to give birth during it. Shucks, what bad luck! Just like that, they have an anchor baby and a whole family of citizens thanks to chain migration. The US immigration system is essentially non-existent.  I'm shocked that airlines are even allowed to do this, but it raises a lot of questions like how you would deny someone a flight for being pregnant and also how this scam is still running if airlines are allowed to stop and reject people for being pregnant and suspected fraudsters.