When Christina of Sweden was born, her parents had been trying to have a male heir for more than five years. During that time, the Queen Consort had given birth to two stillborn babies, and the couple had also lost an infant daughter. So it may have been wishful thinking that led the midwives to joyfully declare that the newborn Christina was a boy. Eventually, her father, King Gustav, decreed that she should have a princely upbringing and become his successor to the throne.
Here’s a link to our notes and research.