The fashion designer and husband David were rumoured to be expecting a baby sister for sons Brooklyn, Romeo and Cruz.
But speaking at her fashion show in New York, the mother-to-be told USA Today that it is not the case.
“I can go on the record and say contrary to rumours, I do not know the sex of my baby,” she said, adding that they still haven’t decided whether or not to find out the gender of their child.
But the 36-year-old said that whatever the sex, she 'feels so lucky and blessed' to be pregnant, and that if it’s a girl she’ll be 'over the moon' but her sons are leaning towards wanting a baby brother.
“We know what to do with boys,” she said, “[and the boys are] excited about having a little brother to teach how to play soccer.”