Credit: Bennett Raglin/

Congratulations are in order for actress Mia Riverton, who gave birth to a baby girl August 26!

The Open House star and her husband David Alpert, executive producer of AMC's The Walking Dead, welcomed baby Hollyn Meiwen after Riverton underwent 42 hours of unmedicated labor.

"What was I thinking?" Riverton, 31, jokes to

Weighing 8 pounds, 13 ounces, baby Hollyn measures 20.5 inches long. "[She] seems to be freakishly strong!" Riverton tells Us. "She's already turning herself over from back to front -- yikes for me!"