The opera singer and her husband, artist Andrew Levitas, announced the news in a statement to MailOnline, which revealed they are expecting a girl.
A spokesperson said: "We are overjoyed to be expecting our first child in the autumn.
"Starting a family and moving into this exciting phase of our lives is a blessing for which we are incredibly grateful. We eagerly await the arrival of our little girl!"
Katherine then followed the statement with a cute Twitter announcement and Instagram photo.