In a selfie video, she posed in a black jacket and black leggings with the bump displayed prominently.
On Thursday, a source close to the couple confirmed to CNN that Teigen and Legend were expecting.
They are already the parents of daughter, Luna, 4, and son, Miles, 2.
Speculation began after the family appeared together in the music video for Legend and Gary Clark Jr.’s new song, “Wild.”
Legend is seen embracing his wife from behind, as she cradles her small baby bump.
Teigen has been open in the past about the couple’s struggles with infertility.
“Once we talked about IVF, it was like I heard everything,” she said. “Some people who are close to us had done it, like, seven to ten times.”
The model and food maven met Legend on the set of one of his music videos in 2006. They dated for several years before marrying in Italy in 2013.
The two are famed for being one of the most beloved couples on social media.
“It was a sad existence. There were no highs. It was a flatline of life for a few months,” she said. “You hear these horrific stories of people not seeing their child as theirs, or wanting to hurt them, and I never felt that way. That’s why I put off getting it checked as I hated myself, not my child.”
Teigen said she was less concerned about it after giving birth to Miles because by then she knew the signs to look for.