I asked my OB about the BH because I was told I was having one during my NT scan (couldn't feel it). The OB said they start somewhere around 10wks, it's just that you don't feel them until later. I started noticing the firm belly early in the 2nd tri. I ususally noticed it when I'd just gotten into bed. It seems to have changed it's routine now though, because I've noticed it at other times recently and instead of when I'm in bed...