Parturition
Dog Giving Birth, by augatti
Parturition then begins with a series of uterine contractions that lead to expulsion of the first fetus. The placenta for each fetus will often pass shortly thereafter. The mother licks away the membranes to clean and stimulate the puppy, and she may also eat the placenta.
The process will continue until all of the puppies have been born. At that time the contractions will cease, and the mother will continue to clean and nurse her young.