I bought stuff even before I was pregnant (but, a few years ago now lol and all sale items) and stashed them haha.
When I got pregnant I bought baby slings right from early on but didn't start buying more clothes til after 12 weeks, and it was just one or two items at first, but I've chosen not to have scans so that wasn't a factor. I felt like I 'shouldnt' buy stuff too early just in case.
I started buying properly after about 16 weeks and now I have more than enough lol. Need to stop now as I have more than enough first size and then need to get that ready (washed) and put away and then go through other stuff I bought (in bigger sizes!) and work out what I will need (probably just vests and a few babygrows/sleepsuits haha, I seem to have accumulated quite a wardrobe already!)