Why wouldn't you communicate ahead of time that you're going to be taking a chunk of time off in the near future, specifically for something so important?
Is he supposed to let HR know when they are trying to conceive? That seems unreasonable and TMI…
I agree that employees should give sufficient notice for something like that. But even if they don't, that's not grounds for firing. It might be grounds for disallowing the leave until the required notice period has passed, assuming that's documented and legally allowed.