It is normal for the sac and the placenta to come out with each puppy. It is also normal for the mother to EAT the sac and the placenta.
placenta
are membrane that helps
this is called the placenta
This is the birth sac that needs to be removed so the baby can start to breathe. If you are talking about the sac that shows on an ultrasound, this is the amniotic sac that contains the 'waters' and is absolutely necessary for the growth of the baby. It is the same thing that the answer above mentions.
Inside of your belly is a umbilical cord going to your embriotic sac (the thing the baby is in) from the placenta. The placenta takes some of the nutrients from your blood and passes it through the cord to your baby. This is why your baby eats what you eat, and is why you can't smoke or drink without risk of harming it.
the yolk sac and the allantois
The allantois, yolk sac and part of chorion.
placenta
Amniotic membrane or amniotic sac, containing the embryo and amniotic fluid.
The allantois, yolk sac and part of chorion.
when a dog is in labor does she need to expell 1 sac or placenta for each puppy that she has, what happens if 1 doesnt come out? example 4 puppies, and only 3 sacs or placentas.