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".
"The last few years have been a blur of emotions to say the least, but joy has filled our home and hearts again," Teigen wrote on Instagram in her latest post.
"1 billion shots later (in the leg lately, as u can see!) we have another on the way. Every appointment I've said to myself, 'OK if it's healthy today I'll announce' but then I breathe a sigh of relief to hear a heartbeat and decide I'm just too nervous still.
"I don't think I'll ever walk out of an appointment with more excitement than nerves, but so far, everything is perfect and beautiful and I'm feeling hopeful and amazing," she added.
The couple are already parents to daughter Luna, aged six, and son Miles, aged four.
In December 2020, following the loss of the baby, Teigen said on Instagram that she was sad she would never be pregnant again - but did not clarify in her post why she believed that would be the case.