I've always been strongly opposed to anyone in the room other than my husband but my whole family are of the same opinion so it was never really an issue. Also I liver interstate so there was never the crowd of people waiting at the hospital because it usually took a few days at least to get there. Lol
I think just not telling then labour has started and waiting till its over will definitely work. But if they've spent 9 months thinking they'll be there then suddenly they weren't might be a bit sad. I would just start saying things now in response to these remarks. When someone says "Oh I can't wait to be at the hospital waiting to hear if it's a boy or a girl" just say "well actually i just want it to be me, hubby and baby for the labour, birth and first few hours while I recover". I think making an announcement at the baby shower might be a bit awkward but definitely letting it come up in conversation and addressing it all at once will get it over and done with well. I worry that you'll have a whole bunch of people argue against the decision and band together against you tho.
You will have to be firm tho. I had to tell the same family members and friends NO they are not welcome to visit my son while he's in the NICU. In th3 end my rude ******* In-laws got sick of hearing No and booked their flights regardless. Lucky for them he was discharged a few days before they arrived. But seriously you will have to be FIRM.