Her temperature will drop below 100*... Do a search of the site, several of us have answered this in detail under similar questions recently.
If you have any questions after reading those... leave it in my "shout out" box and i'll do my best to help.

 One of the ways you can tell a pit bull is about to give birth is by taking her temperature rectally. A normal dog temperature is between 100.3F to 101.3F. But eight to twenty four hours prior to giving birth this temperature will drop to 98 F. The pit bull will also decline to eat anything just when she is about to give birth.