I too think First Response is the only one that you can test as early as 4 days before your period, but I'm not sure why it's any more accurate than other brands, I looked on a site that showed how much HCG it can detect and First Response was in the same field as Clear Blue so I'd try to wait until the day of your period. The longer you wait the higher the HCG and less chance you'll have of getting a false negative. The brown blood could be implantation bleeding, brown blood is old blood so thats good. Goodluck! We may be pregnancy buddies...I'm in my 2WW too.

Good luck to us both...and anyone else TTC now too.