The 38-year-old singer discussed using in vitro fertilization in an interview with Cosmopolitan following news he and Teigen plan to have a second child.
"Having a baby is a big challenge for a couple, and going through that together strengthens your bond because if you make it through [having a child], you know you can make it through anything," Legend told the magazine.
"I think it's especially difficult when you can't conceive naturally," he added. "You want to feel like everything's working properly and want everything to be perfect, but sometimes it's not."
"I wouldn't say we can't conceive naturally, but I would say that it's enough of a challenge where it felt like we needed help," the star said. "We're lucky that we're living in an age where we can conceive in other ways. [IVF] brought us Luna and hopefully it will bring us a few more awesome kids, too."
Legend and Teigen used in vitro fertilization to conceive daughter Luna, who was born in April 2016. Teigen confirmed in an interview with Cosmopolitan this month that she and Legend plan to have another baby.
"We're going to try to have a child," the 31-year-old model said. "We're going to have to do something super hard, which is the IVF process, all over again."
Teigen had told Entertainment Tonight in January that "a little boy" is next for her and Legend. She later explained on Twitter, "I said our next baby would be a boy because that is the embryo we have left" from the IVF process.