Dogs may be able to sense pregnancy, but research hasn’t proven it

A pregnant person's dog may detect changes in their scent, but it is unlikely that the dog understands the reason.

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A pregnant person’s dog may detect changes in their scent, but it is unlikely that the dog understands the reason.
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Capifrutta/Shutterstock

You’ve probably seen bomb-sniffing dogs at the airport or heard about dogs sniffing out cancer. But how far can a dog’s nose go?

People have shared personal stories of their dogs acting differently after they become pregnant. And while researchers don’t have a definite answer about whether dogs can sense pregnancy, there is some research that suggests it’s possible.

Dogs may be able to sense pregnancy through hormonal changes

Research has shown that dogs can detect prostate, bladder, and ovarian cancer in humans by sniffing urine samples. These samples contain biomarkers for cancer, called volatile organic compounds, which researchers theorize the dogs can smell and identify.

And since one of the first signs of pregnancy is an increase in the human chorionic gonadotropin, or hCG, in the blood and urine, it is possible that personal accounts of dogs acting differently could be a result of the dog responding to the scent of hCG.

But here’s the catch: dogs who can smell cancer have been trained to do so. They didn’t know what to sniff for until they were trained. Rachel Barrack, a doctor of veterinary medicine, says that although a pregnant person’s dog may detect changes in their scent, it is unlikely that your dog understands the reason.

No formal studies exist to prove that dogs can smell hormonal changes in pregnant people, though there is evidence that dogs may pick up on other human hormones.

For example, a 2015 study published in Physiology and Behavior reported that dogs and their owners had similar levels of cortisol – the stress hormone – during an agility competition.

Now, the dogs’ cortisol levels could have been from the stress of the competition or a reaction to their owners’ behavior. Yet when researchers accounted for this, they discovered that the best indicator for a dog’s elevated cortisol levels was elevated levels in its owner, suggesting that dogs were reacting more strongly to hormonal changes than to the stress of the environment.

A dog’s sense of smell is much more powerful than a human’s

A dog’s nose runs all the way to the back of its throat, and a dog’s sense of smell is about 1,000 times more sensitive than our own.

“Much of the dog’s brain is dedicated to analyzing odors, allowing them to differentiate scents,” Barrack says. And it’s the same across breeds.

The dogs most often picked to be bomb- or cancer-sniffing dogs are German shepherds, Belgian shepherds, and Labrador retrievers. This is not because they have the strongest noses but because they’re the most easily trained.

So is it possible for dogs to detect pregnancy? It’s doubtful that a dog could sniff out pregnancy without any training. But based on dogs’ responses to other human hormones, perhaps one day researchers will find proof.

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