My latest (would have been 15weeks now) showed up as a pos at ~7w1d but I did not bother getting an U/S or anything because I lost it.
My DS I was ~8-9weeks.
My angel bub I also tested ~8-9weeks.

All but my first pregnancy I tested numerous times leading up to the BFP and each were BFNs. I had a standard ultrasound at 5weeks with DS and they could not find anything but at my dating scan I was 10weeks so I was definately UTD when they done the first one.