The JLS singer and his fiancée Sarah Richards - who have two-year-old son Grayson together - had planned to tie the knot this summer but have decided to wait now they are expecting their second child.
He told Britain's HELLO! magazine: "We were planning to do it this summer but the pregnancy changed our schedule. It will be nice for our kids to be there too."
Aston heaped praise on how well his dancer partner has adjusted to motherhood and pregnancy.
He said: "She's incredible. She's always been very into fitness and had an athletic shape so, for her, the change has been massive. I'm very proud of her."
Aston previously admitted he doesn't want more than two children.
Sarah previously said: "As soon as Aston found out [I was pregnant], he was like, 'Let's do this, but that's it!'"
Aston added: "Honestly, I had always said that I was never really interested in marriage and kids.
"Before meeting Sarah, I just wasn't bothered and I was younger.
"But our relationship built and I thought, 'Yeah this is the forever one.'
"I was always happy with one kid, but at the same time, I can still carry two, so it's perfect."
Sarah added: "And we won't be outnumbered! For Grayson to have a sibling will be really lovely, especially so close in age."
The couple believe becoming parents has made their relationship "complete".
Aston said: "I think kids complete your relationship."
Sarah added "We get it now, but we didn't before.
"We saw our friends having babies and we were like, that's lovely, but we're happy living the life we lived.
"But now, oh my goodness, it's a whole new level of love, even my love for Aston when I see them together."