Do dogs know when you're pregnant? The unique phenomenon explained by a veterinarian.

So the strip came back with two lines, you may not be the first to know. It's a commonly held belief that dogs can sense pregnancy. Some say they even see changes in their pup's behavior before they even know themselves that they are pregnant.

So what, if there is any, is the science behind this? To find out how much of this idea is fact and how much is fiction, we consulted an expert.

Here's what Dr. Camille Alander, a veterinarian with NYC's Bond Vet had to say about dogs sensing pregnancy.

Can dogs sense pregnancy?

While there is no hard scientific backing to the idea, Alander does say that it bodes well for the theory that dogs can sense cancer, decreases in blood sugar, and can help find missing people.

"Dogs have an absolutely incredible sense of smell," she said, so it's not out of the realm of possibility that with the hormone changes caused by pregnancy, a canine might be able to sniff out the condition.

People absolutely have reported that they knew they were pregnant because their dog began to act differently, Alander said. She jokes that signs from your pup should not be used in lieu of a pregnancy test.

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How do dogs act when they sense pregnancy?

A lot of people report that dogs will become more clingy or more protective, Alander said.

In a sitting setting, which is where most of Bond Vet's clinics are located, clients have reported that after pregnancy, their dog would become difficult to walk, she said, trying to attack nearly every other dog that passed by.

Alander also offered up the example of a dog following their owner to the shower in the morning and sitting outside the door until they were done. She described the change in behavior mostly as "subtle things that other people probably wouldn't notice as a change, but because you know your pet well you would probably pick up on."

Can cats sense pregnancy?

Cats have a strong sense of smell just as dogs do, but are not often used in cadaver detection or other pursuits in the same way because they are not as trainable, Alander said.

It's not out of the question in terms of pregnancy though, she said, saying some clients have told her as soon as they got pregnant their cat wanted to sleep on its belly every night.

While they might be able to detect pregnancy, the personality change in a cat is not going to be as noticeable, Alander said, because of their general demeanor.

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This article originally appeared on USA TODAY: Can dogs sense pregnancy? Signs your dog knows you're pregnant.