The 32-year-old model and television personality said in an interview with E! News published Thursday that she plans to keep details about her unborn second child private for as long as she can.
"We knew when we put [the embryo] in but John was like, 'Make sure you don't say it. Let's have one thing for us,'" Teigen, who conceived via in vitro fertilization, said.
"Of course I'm probably going to end up saying it but I'm just going to do this favor to him for as long as I can," she added.
Teigen and Legend already share 21-month-old daughter Luna Simone, who was also conceived via IVF. The model said she and Legend have yet to choose a name for baby No. 2, although Teigen gets to pick this time around.
"Names are tough," the star said. "What I learned was never share your ideas. If you have a name idea, somebody is going to be like, 'No, I knew a person by that name in high school and they were gross.' That always happens."
"John picked Luna so I decided I get to pick this one. I don't what to do. Take it to Twitter," she joked.
Teigen showed off her baby bump at the Lip Sync Battle Live: A Michael Jackson Celebration event Thursday in Los Angeles. She told Us Weekly on the red carpet that she hopes Luna and her sibling get along.
"You think about your first baby, and you're like, 'Are they gonna get along? Are they going to like each other?'" the model said.
Teigen told Entertainment Tonight in January 2017 that she and Legend would have "a little boy" next. She confirmed her second pregnancy in November by sharing a video of Luna touching her baby bump.