Possibly a bit of a daft question: Is it possible that my dog may be pregnant without showing any signs of being so @ Five Weeks. After planning our first Litter over the past 3 years it looks like my baby girl may have missed. We did have all the progesterone Tests (and obviously all the health tests associated) but alas we see no signs.

Some trim bitches will keep their condition a secret until by around 7 weeks, you SEE the puppies moving around.   I usually knew, by how they were acting, whether mine had taken or not, but even at 5 weeks, not necessarily.    On the other hand I had one who was big at 5 weeks, but got no bigger.   She produced 2 puppies and I'm fairly sure may have reabsorbed.   Which is why I never bothered with scanning.   It only confirms or not, a pregnancy at the time of the scan.   Not that they will carry what shows up, to term.    And with mine, the vulva didn't go back to how it was even if they'd had a few seasons before being mated, if pregnant.

In a fit maiden bitch of a medium to large breed, especially those with broad or stocky build I would not be certain of pregnancy by sight until maybe 7 weeks.

At five weeks with a large litter I might suspect a pregnancy.

You could try having her scanned? I must admit with my first girl's 2 litters I was never entirely sure until the last few days, and without scanning or the vet palpating wouldn't have suspected anything - she only had small litters, a 2 and a singleton.