The 30-year-old model announced the gender in an Instagram post about her first ever Vogue cover.
She wrote: "So proud and honoured to have shot the cover of Vogue Thailand. So excited to have shot a Vogue cover annnnd a couple minutes after this shot, John and I learned we were having our little baby girl."
Teigen announced she was expecting her first child with John Legend in October 2015, after her publicly-known fertility struggle.
She wrote on Instagram alongside a sweet black and white photo of the couple: "John and I are so happy to announce that we are pregnant.
"As many of you know, we've been trying to have a baby for a while now. It hasn't been easy, but we kept trying because we can't wait to bring our first child into the world and grow our family.
"We're so excited that it's finally happening."
Prior to the announcement in late September, Teigen had told co-host Tyra Banks on their daily talk show: "John and I, we're having trouble. We would have had kids five, six years ago if it had happened.
"But, my gosh, it’s a process."