I must admit that when I went into labour both times what I was wearing was the last thing on my mind. I looked like a TOTAL dag both times and it didn't occur to me until days after.
I found that I got unbearably hot during labour. Even with Phoebe and she was a day off being a winter baby. I would strip off layer by layer until I was starkers. The thing was that I'd go to the loo or something and just couldn't be stuffed putting my pants back on, etc. I did wear a top both times, with P it was a singlet and with N a t-shirt but I whipped them off when the babies were born so we could have skin to skin cuddles and a breastfeed.
So both times, while I am usually very modest about what I wear, I ended up firstly looking like a complete dork and secondly getting my kit off by the end anyway.
If you are particular about what you want to wear, my advice would be to get it ready now cause when you go into labour you may very well not care a bit.

Having said that, my mum told me that she knew she was going into labour with each of us because, even though the pains weren't necessarily stronger or different to other pregnancy pains at first, she had an intense urge to wash her hair. PMSL! I was the complete opposite! When I was actually in labour I found myself with greasy hair in completely unattractive clothing.