(Reuters) - UnitedHealth Group Inc added more members to its health plans in the third quarter, helping it to post a profit well above Wall Street estimates and boost its earnings forecast for the year. FILE PHOTO: Traders work at the post where UnitedHealth Group is traded on the floor of the New York Stock Exchange (NYSE) in New York, U.S., January 31, 2018. REUTERS/Brendan McDermid/File Photo The largest U.S.