If the progesterone levels indicated birth should be going on and the pups were all lined up and the pups were fully formed (had hair and everything) they were full term.
If she had a lot of pups the uterus may well have been too stretched to allow contractions.
The uterus has muscle tone through out the pregnancy. Its one big muscle.
You may find this article on dystocia interesting reading
http://www.harcourt-international.com/e-books/pdf/974.pdf
It goes into causes of uterine inertia about halfway through it.
Hope this helps you!
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