The Sacramentary Supplement indicates that the Roman Martyrology for Christmas day contains a formal announcement of the birth of Christ in the style of a proclamation. It begins with creation and relates the birth of the Lord to the major events and personages of sacred and secular history. The particular events contained in the proclamation help to situate the birth of Jesus in the context of salvation history.
After the greeting of the Midnight Mass, the celebrant or another minister will introduce the proclamation with these or similar words.
Throughout the season of Advent, the Church has reflected on God’s promises, so often spoken by the prophets, to send a savior to the people of Israel who would be Emmanuel, that is, God with us. In the fullness of time those promises were fulfilled. With hearts full of joy let us listen to the proclamation of our Savior’s birth.
The deacon (or other minister) then proclaims the birth of Our Lord Jesus. This proclamation can be found with and without a musical score at http://www.usccb.org/liturgy/lityearresources.shtml
There is also a proclamation during the Ephipany Mass that sets the time for the coming of Easter. It can also be found at the same location on the USCCB website.