
Agree with annastasia, mine show expansion in the ribcage around week 5. And maiden bitches often show later than that. I've even had bitches that didn't look pregnant until the week before they whelped. One of my girls didn't show until the last week, and was so small that I expected one pup (small breed.)
The night before she whelped was amazing. Talk about rumbling tummies, I literally saw them moving down in waves - it was magic. I thought I could feel 3, and she whelped 3 the following morning. I had already told my friend that there was only one puppy, I was that certain!