During the last days of pregnancy a bitches body temp will range from 100.8 to 100.2 degrees F when taken at rest. The drop that signals labor is 98 to 99 degrees F. It is a fairly good rule of thumb that the first puppy can be expected within 24 hrs of temperature drop.
Loss of appetite or poor appetite.
Seeking a place to hide and seclude themselves.
Some bitches will go to great lengths to build a nest by rearranging or pushing bedding around with their nose. This stage can last many hours and it is during this time that the cervix begins to dilate.