Due in May, the child would be the second female child for the 34-year-old princess.
Normally, the royal family does not reveal the sex of the child to be born.
Spanish officials have promised to repeal a law making male offspring the only heirs to the throne. If it passes, Letizia's first child Leonor, born last October, would be the heir to the throne.
Celebrity Families of 2014 [PHOTOS]