Clarkson, 31, who claims that she will give birth to a baby girl, has already picked a name but refused to share, reported Us magazine.
"I want babies like right off the bat! Well, I'm totally gonna have a girl. My first child will be a girl-I know it in my soul," she said.
The 'American Idol' winner became engaged to Blackstock in December 2012, and had shared the happy news with her fans via Twitter.
"I wanted y'all to know! Happiest night of my life last night! I am so lucky and am with the greatest man ever," she wrote.