The care of a pregnant dog actually begins a long time before they are bred, regardless how determined is the prospective mother or the gentlemen on the other side of the fence. Her background should be examined, she should have a thorough physical exam beforehand, she should have all her shots, and a regular worming schedule in hand.
Once the mother is bred, she should be given a good dog food which is full of nutrients and all kinds of healthy stuff in it. One of the best on the market is Science Diet, or find one that is pretty comparable. The quality of food is associated with the quality of the puppies who will be arriving in about 8 weeks, and the shape of the mother when she gives birth. She should be on this diet until two weeks before she gives birth, where she will be changed over to a Science Diet puppy food with extra proteins and the needed vitamins and nutrients for the puppies she is carrying inside. The change over should be a gradual one, with about half and half at the beginning (one cup adult food to one cup puppy food) with more puppy added after a one week period, or a serious diarrhea will occur. By the time the puppies arrive, she should have been already on a full puppy food diet for awhile.
To make sure she is carrying the puppies okay, it is a good idea to have a vet exam about half way through the pregnancy, to make sure they are lying correctly, they are not too large, or her pelvic area is ready for birthing. Otherwise, a C-Section may be required for the safety of the mother and the survival of the puppies. If so, a due date may need to be scheduled based on the size and condition of the mother and her puppies.
A routine worming is mandatory for the mother dog at the time she is bred and two weeks before she has her puppies. Roundworms are deadly for pregnant puppies and dormant hookworms will regenerate in a stressed mother dog, so a good three day Panacur worming is excellent by the vet or one of his own choosing.