Many dogs will never visually show during a pregnancy, and the ones that do will only show a few days before giving birth.  Instead you should look to the behavior of your dog:

• Changes in appetite – some dogs will eat more, while others will ignore their food altogether.
• Prominent nipples
• Increased sleeping / lethargy
• A clear discharge from the vagina
• A firm abdomen
• “Nesting” behaviors – digging and scratching at bedding, floors, etc.

When your dog is close to giving birth, you will see a decrease in appetite and a increase in nesting, restlessness, and panting.

There are some new products on the market that will help you find out if your dog is pregnant, but they are still out of reach for the home user.  One such project is ReproCHEK, which will determine pregnancy within 15 minutes, but is expensive ($500) and requires the pet owner to draw blood from their pet.

So even in this day and age of technology, intenet knowledge and wonder drugs… the best sure-fire way to find out if your dog is preggers, is to see your vet.