My wife and I breed dogs (Cavaliers). One of the first signs you'll see is that the nipples start to change, usually around 3 to 4 weeks. If you need to know before then, you'll have to see a vet. It isn't til the last 3 weeks or so that the girl really starts getting big.

We always want to know how many puppies the girl is carrying so we know when all the puppies are out, so we get our girls x-rayed about 5 days before the due date. My wife is on some breeders forum and there are a couple people who maintain that ultrasound can damage puppies in rare cases, so we don't use ultrasound; better safe than sorry.

The litter we have right now is a perfect example of why to get your girl x-rayed. Our girl gave birth to 5 of the 6 puppies, about an hour apart, and contractions just stopped; nothing. Nothing for 3 hours. We decided we had to give her a shot of oxytosin; within 15 minutes of that shot, out came number 6. We could very easily lost number 6 had we not had the girl x-rayed and assumed we were done.

Good luck!

Bruce