Flying when pregnant??


So I'm 30 weeks almost 31. When would it be not safe to fly or is it already not safe. And if so would it be safe to take a bus? I am in Mesa AZ trying to get back to Provo UT it's a hour and 27 minute flight. Vs a 17 hour bus ride from Mesa to St George then another 6 hour drive to Provo. Would I be okay to fly? If so when do you think I'd not be okay to fly?