I think they usually send out press releases to that effect. Harry and Meghan’s press releases are just different.
It appears to me that Meaghan is changing how the KP press officers that work for Harry and Meaghan perform their PR. PR for W&K is still typically work focused in a traditional royal manner. However, Meaghan and Harry’s PR seems to be taking a turn towards typical celebrity PR tricks.
Even Rhiannon Mills, Sky News’ royal correspondent, commented on Monday that the royals typically did not make such announcements before major events or tours in order to not detract from their work. In other words, the baby announcement on Monday was not normal for the BRF.