I am trying to remember what I even did with my first (hospital MW birth). I know that I arrived in my own clothes and then I was in and out of my own robe... I spent a lot of time in the shower and walking around. When things got really tough I ended up naked in just a bra and as I recall, that is how I gave birth. I don't remember anyone saying anything at all about what I was to wear (or not wear). I was happy to wear the gown more like a robe for the day after DS was born (he arrive at 4:22AM) b/c I didn't want to bleed on my own clothes and it made it easy to BF. After that I wore my own clothes (we were there for 4 freaking days). Nakedness in labor (especially at the end) just didn't bother me at all and its hard to see why it would bother anyone else there. The second time (at home) I made sure to wear my "less good" bra so as to keep the other one clean and dry to change into. (very ample bosomed, I am much more comfortable in a bra, especially doing strenuous things like giving birth).
Hospital gowns- honestly? - Page 2
I'd definitely recommend a hospital tour if you haven't taken one. It is a good chance to ask the nurses what they prefer, what the hospital requires, etc. Our hospital showed us where the drink station was so we could help ourselves, showed us where they keep witch hazel soaked pads in the freezer, etc.
I made a couple of skirts beforehand that I didn't mind ruining (made them out of old T-shirts from Goodwill), and I figured if I wanted to change, I would, and if I didn't want to, I wouldn't. Normally I hate wearing PJs/frumpy clothes in front of people; I feel self-conscious and weird. (not that I wear PJs in front of people habitually, but in college in the dorms I would, and I tended to feel self-conscious and weird.)
So I showed up to the hospital wearing one of those skirts and an old T-shirt of my husband's, with an old front-closure bra underneath (I figured that would be easier to unfasten for skin-on-skin and breastfeeding later, and I do hate knocking around without a bra; it's uncomfortable). They showed me to triage and pointed out the gown hanging on the wall, then left us for a bit. I got on the bed (that was a mistake! Should have stayed standing like a PP did!) and when the triage nurse came in she said I should put on the gown. I said I'd rather wear my own clothes and if they got wrecked I didn't care. That was the end of it. Ultimately, I didn't care at all what I was wearing or who saw me in it, but contractions were 1 1/2 minutes apart by the time I was in triage and I had no interest in changing, so that was what decided me. I did end up in a gown eventually--honestly can't remember if I changed after baby was born, or right before pushing. I put it on backwards so it opened in the front, and opened it to do skin-on-skin. At that point I was fine with changing and getting out of the grubby clothes I'd been wearing during labor.
I also wore the mesh undies post-partum; they were great for holding those two-foot-long pads and icepacks, and I could go through as many pairs as I wanted. I wouldn't have wanted to have my own undies in the hospital. After I went home, though, I regretted not having more cloth pads, even though normally I hate pads and I probably wouldn't use them again for periods, because after a week or so wearing a synthetic pad got really uncomfy (which is WHY I hate pads, and if I'd realized this I would have made sure I had some cloth for postpartum).
Anyway, I wouldn't sweat it too much... they can't make you change, but you also don't know how you might end up feeling once you get there, so I'd just wear something you want to labor in and just go with the flow from there.