I was talking to a girl I work with and she mentioned that she was 19 weeks and due 11/29. Well, I'm 20 weeks and due 11/24. I was just wondering how can she be further behind in her pregnancy but due after me? Is it just based off when she had her last period or based on baby's measurement or something else? I just thought it was really weird when she said that. Please no judgment, first time mom here..