Opting for all white, the mother of two wore a calf-length, fitted white dress, accented with triangular, metallic cutouts, which showed off her waist.
A rep for Blunt, 33, confirmed the pregnancy news to PEOPLE in January, just five months after Krasinski, 36, joked about giving their daughter Hazel siblings.
“Hopefully one day we will!” he told Entertainment Tonight. “One day, I don’t know when. We’ve got to give her some competition at some point.”
Months later, in June of this year, the couple welcomed their second daughter, Violet.
“What better way to celebrate the 4th… than to announce our 4th family member!!!” Krasinski tweeted a few weeks after Blunt gave birth. “Two weeks ago we met our beautiful daughter Violet.”
The pair welcomed their first daughter, Hazel, in February of 2014.