[The_Colonel]

> Because they're fathers, not mothers.

They gave a birth to the child, something only mothers can do.

> You also have many families with adoptive mothers who didn't give birth to their children.

Well that's my point. Using the term "mother" is just fine for them. That doesn't make a necessity to always differentiate by emphasizing that a given woman is "birth mother" / "birth person". In most cases (including LGBT/trans) using the term "mother" is fine and there's no need to go more specific than that.

> And I'm pretty sure even children can understand the term pregnant person. I'm surprised that so many people here are confused by it

It's not confusing, use it, if you wish, but I prefer the term "mother".

What people are annoyed with is the language police, imposing your preferred usage on others. The host being pushed to apologize for using the term "mother" is just absurd.