The celebrity couple, who have been together for nine years and married for two, announced the news on Teigen's Instagram account.

"John and I are so happy to announce that we are pregnant," the Sports Illustrated model wrote, alongside an image of the pair.

"As many of you know, we've been trying to have a baby for a while now. It hasn't been easy, but we kept trying because we can't wait to bring our first child into the world and grow our family."

Teigen, 29, added that she looked forward to "all the belly touching".

The news comes just days after a television interview with Teigen aired in which the model said trying to have children had been a "process" for her and her musician husband.

Speaking on Tyra Banks' new daytime talkshow FABLife, Teigen said she was sick of people asking women when they were going to have kids.

"Anytime somebody asks me if I'm going to have kids, I just am like, one day you're going to ask that to the wrong girl who is really struggling and it's going to be really hurtful to them and I hate that," she said.

"So I hate it, stop asking me."

Teigen and Legend, 36, met on the set of the video for Legend's 2007 song, Stereo.

They became engaged four years later during a holiday to the Maldives and married in September 2013, in Como, Italy.

His platinum-selling song All of Me was written for Teigen and was released one month before their wedding. The couple both star in the song's music video.

Teigen and Legend often take to social media to openly share elements of their relationship.

Earlier this year, Teigen livetweeted a lazy Sunday the pair spent without getting out of bed.