TBH I think its always going to be dodgy when you're having regular shots and if you're sensible, you shouldn't do a HPT at all and just wait for bloods. Of course, I don't take my own advice and so I POAS in the morning that my next pregnyl injection was due (I was having a shot every third day so roughly 72 hours after my last shot). I got what I would describe as a medium sort of darkness on my BFP but I had no confidence at all and was actually really surprised when they rang with my blood results and a BFP