The actress told People.com she and her husband, Shane Aaron, are expecting their daughter to be born May 24.
"It feels wonderful. This is the most joyous time of my life," Castillo said. "It feels great to finally be able to share it with the world."
The couple married in 2008.
Castillo's character on "GH" discovered on Monday's episode she is pregnant with her ex-fiance Patrick's baby. Patrick, played by Jason Thompson, left Sabrina at the altar this month when his presumed-dead wife, Robin, played by Kimberly McCullough, returned to reclaim her family.