The star and her fiance, musician Martyn LeNoble, became first-time parents to little Sadie Grace last month (Jan11).
Applegate admits she doesn't "have a good relationship" with her chest after undergoing a double mastectomy to treat breast cancer in 2008 - but she battled her fears while she was in hospital.
Speaking to U.S. talk show host Ellen DeGeneres about the birth, she explains, "Just that moment, pulling her out and I dropped my gown which I don't do. This part of my body (my chest) is very private to me... that's a real private place. A place that I don't have a good relationship with, let's say.
"But at that moment of pulling her out and I just tore that thing (gown) off. There's a room full of people that I don't know. Nurses and doctors. And she and I just lay there. It was the best thing that's ever happened to me."