Would it be considered kosher (in US) during a job interview with a noticeably pregnant woman to make normal pregnancy-related small talk? Like asking when she’s due, gender known, names picked out, etc?

No, unfortunately. Even if it is totally innocent, if the candidate does not get the job, they will likely file suit that it was strictly because she was pregnant and the company didnt want to hire someone who would be out for several weeks shortly after starting. Turns in to a very messy situation.

I forgot to explicitly say it wouldn’t effect their decision, but you’re probably right, it doesn’t matter.