The 37-year-old singer and 39-year-old former NHL hockey player star in a new four-part web series, Mike and Carrie: God & Country, from the non-profit I Am Second.
In a trailer released Sunday, Underwood and Fisher discuss their marriage and family. The couple married in July 2010 and have two sons, Isaiah, 5, and Jacob, 16 months.
"You know, marriage is a giant mirror and it's a magnifying glass, too," Fisher says.
Underwood shares how she and Fisher "differ drastically." The couple initially had different views on starting a family.
"I always wanted, you know, lots of kids," Fisher says.
"I was never good with other people's kids. Why would I be good with one of my own?" Underwood remembers thinking.
Fisher recalls how Underwood experienced three miscarriages in two years before becoming pregnant with their son Jacob.
"You have all these mountaintops but we hadn't had a ton of valleys like this," he says.
Underwood says she had "an honest conversation with God" during their fertility struggles.
Underwood previously discussed her miscarriages in an interview with People in July. She said she struggled with her losses but ultimately put her future in God's hands.
"I get to do what I love, I have an incredible family," the singer said. "I have all these amazing people around me, and I don't want to complain, ever."
"But the miscarriages made me get real with God and say, 'Okay, I'm kind of giving up a little bit. If this isn't mean to happen, then I need to accept that and know that someday I'll understand why,'" she recalled.
Underwood shared a photo of Fisher with their sons on Instagram in April.
"Mornings at the Fisher house," she wrote.
Mike and Carrie: God & Country premieres Wednesday at 8 p.m. ET. Fisher previously filmed with I Am Second, a Christian multimedia project, in 2014.