fedup, you clearly don't understand how roundworms are transmitted during pregnancy from the mother to the pups. The majority of dogs carry roundworm eggs encysted in their bodies when they are not pregnant. These will stay dormant until the hormones of pregnancy activate them and they will then be transmitted to the pups, without showing up in a stool sample from the mother because they are not passed in her stool, they are transmitted to the fetus.
Honestly, this is what happens when people make stuff up

You said in another post that you've never wormed the mother - not even when she came into season - so it is very likely that she will transmit roundworm eggs to puppies. By the time you even detect these in puppy stools, they will be 3 weeks old and have lived with parasites for the first 3 weeks of their lives, when they are trying to thrive and when things can hang in the balance.
I'm done on this thread, I've tried to pass on best practice and what is considered best practice by just about every dog organisation anywhere. You can want things to be other than how they are, but unfortunately they are not that way.
Tommee, I've no idea what vaccinations have to do with this. When I tried to mention them several posts ago, I was told that the OP wasn't saying anything about vaccinations. So please don't bring them up, because you can't have it both ways...