Hello,
Hoping to get backed up by the Etiquette experts here but I have a story to share. If this prevents just one person from unintentionally hurting someone's feelings, it's worth it.
I have a beloved relative who was recently diagnosed as Bipolar. She's been an absolute hero dealing with it, holding a job, raising a small child, being a supportive wife, and facing it head on. Her husband has been wonderful as well. Of course, many medications for this disease cause rapid weight gain, sometimes as much as 12 pounds in a week or two.
You WOULD NOT believe how many women (WOMEN!) who have asked her if she is expecting again. I doubt all of these people are horrendously stupid/ignorant/both and probably think it's OK because she's a young woman with a small child. In any case, it is so hurtful as she is already self-conscious due to the weight gain but it's a 1-2 punch as she & her husband have made the difficult decision not to have any more children due to the diagnosis.
In any case, just posting in case anyone, no matter how well you think you know someone, is thinking of asking this. IMO, the ONLY time you can discuss a woman's pregnancy if she hasn't informed you of it is if you literally see the baby crowning out of her vagina.
Ettiquette leaders, please back me up?