She's Glowing! Katherine Heigl Debuts Baby Bump on "Doubt" Set

The expecting star, 37, gave fans the first glimpse of her baby bump on the set of her new show, "Doubt," on Tuesday. She tried to conceal her growing belly under a black knee-length skirt and blue blouse as she filmed scenes for the courtroom drama.

The actress is expecting her first biological child -- a baby boy -- with husband Josh Kelley. The couple is already parents to adopted daughters Naleigh, 7, and Adelaide, 4.

"We've known for a while that we wanted to add to our family and frankly didn't really care how we chose to do that," the former "Grey's Anatomy" star revealed in a blog post last month. "We were considering adoption again, fostering, or pregnancy if possible. Seeing as I have never been pregnant and as my OB/GYN reminded me last year, I'm of advanced maternal age, I wasn't sure pregnancy was even in the cards for us. Turns out it was very much in the cards!"

"This is truly an amazingly blessed time, waiting for the child you've been dreaming of to make their appearance," she added. "Though I've never been a particularly patient person, my experience of waiting for Naleigh taught me a lot in that department. So I will wait and eagerly anticipate, hopefully with grace, gratitude and a good attitude (ummm pregnancy hormones are real people.) Maybe this time the waiting won't be so hard because I'll have all of you to share the laughter, tears and joys of my experience with."