Puppies grow up fast - and can get pregnant at a very young age, too. Here's what to know before you decide to spay your dog or have your first litter.

You have hair on your head, and your dog Fido has fur all over its body. Easy enough, ... It’s just that the cycle in you as a human is longer than, say, Fido’s hair growth cycle.

During your visit, your vet can use ultrasound to see the growing puppies, typically around 4 weeks in. Ultrasound is safe during pregnancy. It uses sound waves to create an image of your dog's womb.