Dogs and pregnancy

Did anyone else's dogs get real protective when they were pregnant? My dog snarled and showed his teeth to my child's father. It was out of the blue and completely random. My only reasoning behind it is either A. My dog can finally sense I'm pregnant and is starting to be really protective of me. (I'm 21 weeks) or B. My child's father is really the only one that disciplines my dog because I spoil him so much and maybe he got tired of him. Anyone have any thoughts, advice, or experiences sort of the same?