"stomach and nipples getting bigger is the only first signs you would be able to tell."
I must say that statement is not correct, once the female has been bred and the heat has ended their rear end will stay soft (like when they were in heat).....often times they will have a touch of morning sickness, not eat very much for a couple of weeks and then start to eat again, often times more than normal.
Having bred for quite sometime now it is easier to see the "signs" thats for sure. When the stomach and nipples start to get bigger is not a good time to notice that your female is pregnat...and NOT a sure way to know as it could be a false prenancy.
Some people use x-ray or ulta sounds to confirm pregnacy, I listen to the heart beats at about 5 weeks after breeding takes place. You can count the pups that way and often tell the sex of the pup you are listening to.
usually if your dog was in heat she will stop bleeding within a day after she was breed.so that right there is your sign that she is pregnant. of course if you not sure about the day that it happens than your best bet is the vet ,they will do an ultrasound and can almost 100% tell you how far she is and how many she will have... good luck