I would tell immediate family and close friends because I would be thrilled. I would not post on social media about an impending C-section because that's very personal. I'm sorry you were not called but just because I would told my sister and she didn't I'd say try not to judge her too harshly. After some time passes, I would sit down and ask her why she didn't tell you. Could it be that you might have made her nervous about it?