Zuckerberg made the announcement on Facebook, saying "After our difficult experience having Max, we weren't sure what to expect or whether we'd be able to have another child. When Priscilla and I first found out she was pregnant again, our first hope was that the child would be healthy. My next hope was that it would be a girl. I cannot think of a greater gift than having a sister and I'm so happy Max and our new child will have each other."
He went on to describe how it was growing up with three sisters and what he learned from them.
His heartfelt note ended with a statement that fittingly came after International Women's Day, "We are all better people because of the the strong women in our lives -- sisters, mothers and friends. We can't wait to welcome our new little one and do our best to raise another strong woman."