The notoriously private couple, who have been married for 14 years, are already parents to a daughter, who will turn 9 this month.
Bale's rep had no comment.
"It's all about my girls, my wife and my daughter. I carry a picture of them with me all the time," Bale, 40, said about his two girls in 2009.
Sibi, 43, debuted her baby belly last Sunday on the red carpet at the Academy Awards, where her husband was nominated for Best Actor for American Hustle, which also scored nine other nominations including Best Picture.