I actually had my mind changed on this one 
DH watches lots of US TV and I think he's influenced by it.
He used to joke around saying "When we're pregnant can I do XYZ?"
It really drove me mad because I'd say, no, we won't be pregnant, I will be pregnant. He got really sad about the fact I wouldn't let him say it. I said I was totally happy for him to say we're expecting, we're having a baby etc but not we're pregnant because it's factually incorrect.
I live abroad so a lot of my English speaking friends are American. I mentioned this annoyance to a few of them expecting them to react like MNers and agree but instead they all made
:(
:( faces and one who I really respect ended up persuading me to let it slide because it was such a common thing to say and just an expression. It still irritated me, but I told DH my friends had deemed me unreasonable and that he could say it. But I'd prefer "we're expecting". Because it's accurate.
Then I got pregnant, and I miscarried at six weeks. Throughout the whole affair he was so involved, invested and basically acting more pregnant than me that I suddenly got it! It might just be the contrast to my ex, who was happy to ignore it unless it was exciting for him in the moment, it might be DH being weirdly involved (he was the one having weird cravings, morning nausea, and mysterious metallic tastes whereas I had none of that) but I conceded that, yes, he was enough of a part of proceedings that I'd reluctantly admit that he could claim some kind of ownership of the process.
It was weird. But yes, it doesn't creep me out as much any more.