Milano, 38, married talent agent Dave Bugliari, 32, in 2009 after dating for about three years.
"They're just over the moon," a friend told People.com Tuesday. "They are so excited."
Milano, who is due to deliver their baby in the early fall, is best known for her work on TV's "Who's the Boss?" and "Charmed."
Swim Week Miami Beach 2014 [PHOTOS]