"I just want to know more about the not knowing you’re pregnant for 29 weeks. Can someone explain to me how that’s possible?"
Don't worry, Dan, not gonna happen to you.
Cases like this make the news every year. Usually a woman who's been gaining weight for other reasons (obesity, inactivity, medication, etc) and so doesn't pay attention to another 10-20 pounds. Is able to explain away other symptoms, eg, due to chronic digestive problems, endocrine conditions.
ETA: I don't mean that they happen on a plane every year! More common is a woman is at home, feels abdominal cramps, goes to the bathroom, and is surprised to see that what comes out is not a bowel movement.