The 31-year-old model announced the news Tuesday by sharing a cute video with daughter Luna.
The clip gives a glimpse of Teigen's baby bump as she asks Luna, "What's in here?" The 19-month-old answers "Baby!" as she touches her mom's growing belly.
"it's john's," Teigen captioned the post.
Teigen and Legend welcomed Luna in April 2016 after conceiving via vitro fertilization. The model confirmed in the October issue of InStyle that she would undergo the procedure again in the hopes of having another child.
"[It will happen in] the coming months," she said at the time.
Teigen told Entertainment Tonight in January that she and Legend will have "a little boy" next. She later explained on Twitter, "I said our next baby will be a boy because that is the embryo we have left" from the IVF process.