Hello and Welcome! Are you a breeder or are you planning to become a breeder? I have no idea, because im not a breeder, but I'm sure somebody else will come along to answer all your questions, everyones very helpful here!
The answer to your question depends on the dog. The actualy pregnancy and whelping does not generally affect the cycle, so if a dog is in heat every 6 months or every year, she will come into heat close to those cycle times, regardless of pregnancy and whelping.