The model has previously spoken about the fertility struggles she and her husband John Legend faced when trying for a baby and now she has revealed they selected their child's gender during IVF treatment.
"I've made this decision," Teigen told People magazine.
"Not only am I having a girl, but I picked the girl from her little embryo. I picked her and was like, 'Let's put in the girl.'"
Selecting a baby's gender before birth is offered in many fertility clinics in America, but it is not allowed in the UK.
According to the Human Fertilisation and Embryology Authority, in the UK sex selection is only allowed for medical reasons - for instance, if you carry a serious genetic condition that you risk passing onto your children, then it could be considered.
Teigen said she came to a decision over the gender of her baby because Legend "deserves a little girl", before adding that she would also like a baby boy in the future.
"I think I was most excited and allured by the fact that John would be the best father to a little girl," she said.
"A boy will come along. We’ll get there too, so it’s not like we really have to pick. But he definitely is very lucky to have a little girl. And this girl is going to be so completely lucky to have John as her papa."
Teigen received some criticism for choosing the gender of her baby on Twitter, to which she responded: