Mariah and Nick welcomed twins - a boy and a girl - on their third wedding anniversary.
A spokesman for the pair said that they were "overjoyed" at their new arrivals, which weighed in at 5lbs 3oz and 5lbs 6 oz respectively.
She also revealed that Mariah listened to her own song, We Belong Together, as she was giving birth.
The couple, who renewed their wedding vows while in hospital, have named their little girl Monroe, after Mariah's inspiration Marilyn Monroe, and their son, Moroccan, inspired by the country where Nick proposed to the star.