Can dogs sense pregnancy???

My dog is about 7 months old, and he's always the sweetest thing ever. He's EXTREMELY emotional. He's never barked at anyone, but just within the past 2 or 3 weeks, he's been growling at people. He doesn't growl at me or my daughter or fiance, but he does at everyone else. And when he does, he comes and sits right in front of me or beside me, and has become very very protective over me. He always follows me where ever I go, and will even sit by the front door when I leave the house and patiently waits for me to come back home. I just took a test this morning, and it was vibrantly positive, so I was wondering if maybe dogs sense things like hormones or something??