The Palin family asked the media to "respect our daughter" and her privacy. According to the Reuters report, John McCain's campaign was aware of the pregnancy when the Arizona senator selected Palin to be his running mate last week.
Update: The following is the full Palin statement as released by the McCain campaign:
"We have been blessed with five wonderful children who we love with all our heart and mean everything to us. Our beautiful daughter Bristol came to us with news that as parents we knew would make her grow up faster than we had ever planned. We're proud of Bristol's decision to have her baby and even prouder to become grandparents. As Bristol faces the responsibilities of adulthood, she knows she has our unconditional love and support."
"Bristol and the young man she will marry are going to realize very quickly the difficulties of raising a child, which is why they will have the love and support of our entire family. We ask the media to respect our daughter and Levi's privacy as has always been the tradition of children of candidates."
Update: Asked about the revelation while campaigning in Michigan, Barack Obama said, "I think peoples families are off limits and people's children are especially off limits." CBS News' Maria Gavrilovic has more.