I was once given a piece of advice which has stood me in good stead, so I'll pass it on :
"Never ask a woman if she's pregnant unless you actually see the baby coming out. This applies regardless of her age, marital status, or sexual orientation."
When I was duty manager for an airline, one of the check in staff came to me and said : "Are pregnant women allowed to travel?" I said yes, up to 32 weeks or whatever it was then. The girl asked me to go and check out this woman. She was young, and very ugly, and looked as if she was about to give birth to elephant triplets. So I simply asked her if she was sure she was OK to travel, and did she have any condition that would make it unsafe for her to fly. She asked me quite unpleasantly if I thought she was pregnant, at which point I was tempted to say unless it was a turkey baster job I think that's highly improbable.
She refused to sign a waiver form so I refused to let her fly partly because I thought she'd upset the balance and trim! Never found out if she was pregnant or not. Somehow I suspect not.