While consulting a veternarian is probably the wisest step to take, there is some general information that is available to you from different sources. One of the basic considerations is the breed of your dog. For, larger dogs generally tend to have large litters 8-12) even if they only mate once during their eleven-day fertility while small breeds have from 2-4.
Before you breed your dog, you may want to consult, not only with the vet, but with a breeder since there often is great expense involved as many things can go wrong. If, for example, a dam has a "mummy puppy" which is one that has died in the womb and comes out looking mummified, the mother will likely suffer an infection of the uterus. Caring for the babies and providing the required shots, etc., before their sale can also become expensive.
It is recommended that an owner not breed her female before she is two years old. By this time, she has fully matured and pregnancy will not take too much away from her physically; also, she will be mature enough to handle motherhood.
Check out the site below and, please, do consult with professionals.