The US model, aged 36, shared an Instagram post showing herself visibly pregnant, saying she was feeling "hopeful and amazing".
"Joy has filled our home and hearts again," she added.
In September 2020, she lost a baby, whom the couple had named Jack, after suffering complications and bleeding.
Teigen previously said that the loss was "the greatest pain I could ever imagine".
At the time, she wrote that she and her husband were "shocked and in the kind of deep pain you only hear about, the kind of pain we've never felt before".