In addition to being man's best friend, dogs are known for their ability to sniff out changes in the human body. For example, in a 2011 study published in Gut, an International Journal of Gastroenterology and Hepatology, a Labrador retriever correctly detected colorectal cancer with 95 percent and 98 percent accuracy in two different sets of human samples. The study stated that a specific smell is linked to cancer, and that's what the pup picked up on.
Similarly, when you're pregnant, all the hormones flooding your body are likely to alter your scent somehow. Not much gets by the canine nose, so there's a chance your dog caught wind of a change in you -- maybe even before you did.
"Although it hasn't been scientifically explored, it's within the realm of reason," says Jennie K. Willis, an applied animal behaviorist with Colorado State University's College of Veterinary Medicine.
However, while your dog may have detected a scent change, according to Willis, it's unlikely he comprehends the reason. So you can still expect your furry friend to raise a puzzled eyebrow when your little bundle comes home. "Perhaps if the dog has been with you for multiple pregnancies, he might make the connection, but it would be tricky," Willis adds.