No gender reveals before birth.
Like many other rules, the royal family members are barred from revealing the gender of their Unborn children before their birth. Even if the family members find out the gender, they are not allowed to disclose it to the public and must at all costs keep this a secret from the prying eyes.
It’s not sure whether members of the royal family are to abide by this rule strictly or is it just a tradition that runs in the royal family. Either way, the public is interested in figuring out whether it is a boy or a girl by observing the clothing pattern of the princesses and ladies of the royal family to make a guess about the gender of the baby before the birth. Well, it’s a lot of pressure anyway.