
Darn. I came back to the page and hit the TU button, losing ALL I'd written but not posted!!
If I can remember what I wanted to say ..... we didn't up the amount our bitches were eating until AFTER the litter was on the ground and we could see how many they were going to be catering for. The last thing a pregnant bitch needs is, like us, to become fat. Provided she's having a good quality food, as always, she'll be fine and the puppies will take what they need before and after birth. Once you see what you have there, then is the time to increase her food. You may find if she gets big inside, you'll have to feed her smaller meals, more often, and cut back on the bulk, increasing the protein if needed. And no supplements. Again if she needs supplementing the time to be doing that is after she's whelped, as required. It is tempting to think more is good, but it's not. Newborn puppies don't take that much milk and if you have too much coming down, she could run into mastitis and the tiny puppies may not be able to cope with lashings of milk either.
As is well known around here (!) I have did scanning. That only says yes or no to a pregnancy and only at the time of the scan. Yes we did have one bitch who seemed to be expanding as normal for her breed (and with a wide long ribcage, puppies could be hidden for some weeks) but by around 5 - 6 weeks didn't seem to get significantly bigger. She had 2 puppies the first time and a singleton the second at which point she was retired, and spayed! The Section she needed for the singleton puppy didn't suggest she'd reabsorbed, but she may have, and ditto with the first litter. It happens. Unfortunately.
As for not walking - just as with letting them get fat, not walking won't help keep her muscle tone up so as long as she doesn't get over-tired, I'd be taking her out for a stroll. At least until her increased girth restricts how much she can do!