The mother will have a discharge which can last for a week after birth.
The first day after birth, the discharge color is red or reddish brown in color. If the discharge is black, call your vet immediately.
The following days the discharge should start to lighten in color, getting a clear look to it. If it last longer than a week or so, or has a really bad odor to it, call your vet immediately.
I hope this info helps and good luck with mom and the pups!