
So difficult to predict as they are all different, just like humans, some show very early, others much later.
I know a FCR who didn't look pregnant @ 8 weeks ~ but had been scanned for at least 9 / 10 pups ;)
everyone who saw her said she wasn't carrying a large litter & 2 or 3 pups may be in there, sure enough out popped 11 healthy pups all of good birth weights. :D
I've seen other bitches at 4/5 weeks in whelp who are very obviously pregnant.
I'd say typically @ 5 weeks a bitch would usually start to change her abdomen shape ~ and 6 weeks would be average for a bitch to start to gain weight (slightly!) & look in whelp.
Obviously different breeds can vary a lot.
good luck.