This is the first child for Whitney and her TV producer husband Tim Rosenman, who tied the knot in 2015 after three years of dating.
The excited new mum wrote a lengthy blog post (featuring two adorable photos) entitled 'Meet Our Son.'
"So, I have some news. No big deal, but I created another human being and then delivered him into the world at 12:30am Thursday morning. Timmy and I named the little man Sonny and I’m in love," she began.
"I just want to talk about how I’m feeling," she wrote. "We’ve all heard mothers give the same speech about how life changing the love for your baby is, and it’s not like I didn’t believe it or anything, but I guess I couldn’t actually connect to those exact feelings until the doctor placed Sonny onto my chest."
Whitney also took to Instagram to share the exciting news, with a photo of a hand-painted sign that read "Welcome Baby Sonny."
"I made a human!" she wrote. "Everyone is so happy and healthy and we are home now. I'm going to try my very best to not be one of those moms whose feed is dominated by their baby but I can totally see how difficult it will be not to. I am beyond obsessed and in love and wish I could bottle this feeling for all of you out there."
Congratulations to the happy couple! Whitney will make an amazing mother!