My understanding is that in the US, clients are often given hospital gowns for medical appointments where they aren't strictly medically necessary, whereas in the UK and Austrailia they are much less likely to be used outside of surgery or medical imaging. (For example, in the US, clients are gowned for pap tests, but they rarely are in the UK--you could just wear a long, loose skirt. Clients are also routinely gowned for non-gyn physicals in the US, but there's not a lot of medical justification for that.) My gut feeling is that wearing gowns makes a significant portion of people (obviously not everyone) feel more disempowered and/or uncomfortable in a situation where they already feel vulnerable, but I haven't seen any formal studies confirming or denying this. I would love to read if wearing gowns increases clients perception of pain or discomfort, or makes people less likely to meet with heathcare providers. Conversely, if there are studies showing that clients who wear gowns have better medical outcomes than those who don't, I would like to see this too.
I have seen several posts in childbirth communities on how individuals felt better laboring in their own (comfortable, loose) clothes, but that's more anecdata.