A rep for the couple did not immediately respond to a request for comment, and the baby's gender was not reported.
The "Gossip Girl" alum, 27, and "R.I.P.D" actor, 38, announced Lively's pregnancy back in October on the actress' lifestyle site, Preserve. The post temporarily crashed the fledgling site. Since then, the expectant mother has been spotted out and about sporting stylish maternity ensembles.
The duo met while filming 2011's comic-book flick
In the August 2014 issue of Vogue, the Gucci ambassador gushed about Reynolds being a dad.
"He's going to be a great father and leader and patriarch — he's so meant to be all of those things," Lively said. "The fact that he lived so much before we got together, he's the exact realized person that he should be. And so I get to share my life with the person he's become, and we get to grow from there."