I honestly couldn't tell much different on my chart the one cycle that I did get a bfp (I ended up having a m/c though).. the only thing was that my temp did NOT drop the day before AF was due like it drops every other time.
Really, for most people I don't think that there is anything you can tell by looking at the chart until AFTER you get the bfp.

It's frustrating, cause we all want to know, and know NOW, but it just doesn't seem to happen that way.
HTH!