Nicole Kidman had the joy of hearing 50,000 fans singing happy birthday to her on Saturday when husband Keith Urban requested backing vocals for his ditty.

The country star was playing at Chicago's Soldier Field when he dedicated his song Who Wouldn't Wanna Be Me to the pregnant actress, who turned 41 on Friday.

He then brought her out on stage and invited the arena's audience to help him make Kidman's birthday extra special.

He told the crowd: "It would be nice to have 50,000 people sing 'Happy Birthday' to her."

After the birthday rendition, Kidman blew a kiss to the crowd and returned backstage to watch the rest of Urban's concert from the side of the stage, reports People.

The couple is expecting their first child together this summer.