John Legend says having a baby ''challenged'' his relationship.

The 'All Of Me' hitmaker admits it was a difficult time for him and his wife Chrissy Teigen in their relationship when they were struggling to conceive naturally but he feels blessed they were able to have daughter Luna through IVF.

He said: ''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.

''I think it's especially difficult when you can't conceive naturally. 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. 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.''

And the 38-year-old singer credits Chrissy for encouraging him to be more open in their relationship.

He added to Cosmopolitan magazine: ''There's no problem with openness in our relationship. You know Chrissy. She doesn't hold anything back! I'm quite reserved, but being with someone like her inspires me to be open about my emotions. She brings them out of me because she's so open about hers ...

''We're always honest with each other, so we discuss everything that's on our minds. When she was thinking about how she wanted to drink less, we talked about it. I just want to support her. I want her to be happy and to live the fullest, most awesome life she can, and I want us to do it together. Whenever she sets her mind to anything, I always tell her, 'I want to support you and help you do it.'''