Prince Harry and Meghan Markle, the Duke of Sussex have announced their baby news at the wedding of Princess Eugenie. In my opinion, I believe it is unacceptable to share such a grand announcement at a wedding.
If a couple does decide to take the plunge and make an announcement, I would recommend that they do so at a more intimate occasion during the whole weekend. For example, maybe at the end of a rehearsal dinner, or at the home of the bride when everyone was gathered, or if there is some sort of after-soiree. Timing in this instance, is key, and you should not take place during any time where the main focus should be on the bride and groom. You can do a covert operation type approach and just tell individuals one-on-one as you are gathered with the family as opposed t making a full-on announcement. Allow your special announcement to be a topic of conversation that could flitter throughout the room - this way you can engage in private conversations as opposed to a big open display.