With my first I had a waterbirth in the hospital. For laboring I just wore their gowns and was naked for the birth. Afterwords I wore their gowns as well, until it was time to go home.
With my 2nd I had a HB waterbirth. For labor I wore a long t-shirt with no pants. My water had broke so I didn't want to have soaked pants from leaking. After a while I got super hot so I changed into a spaghetti strap tank top, which I then wore for the birth in the tub as well. Afterwords I just wore a bathrobe.