Can dogs sense pregnancy?

Can dogs sense pregnancy? My medium sized dog is rescue so he's all about cuddling and getting loved, sometimes when playing with my rescue I'll pat my legs and he'll jump on and like put his front paws on my tummy and we'll start playing but today when I tried to get him to do that he basically he ran away and kind of hung his head like he was being reprimanded. He's never done this before and I'm hoping it means maybe he can sense there's a baby in there? Lol any experiences with anything like this?