
Regardless of the number of puppies (and they will always take all they need, both pre birth, and afterwards) I have usually backed off the 'bulk' in the latter stages of pregnancy - and for sure, with a good-sized litter, there isn't enough space to be eating a lot of food at each meal. Again puppies take what they need so I don't go with holding back on what mum eats as meaning the puppy(ies) won't be as big!! Mum won't get fat, is all.
For me, with a singleton puppy, it's really more about not leaving it too long after the due date without getting it out. All too often a singleton (or even just a couple) puppy sits, growing bigger by the day and making a C.Section more likely to be needed.