Bristol Palin has signed on to MTV’s Teen Mom OG as a new series regular for the upcoming season, Deadline has learned. Palin will join cast members Amber Portwood, Maci Bookout and Catelynn Lowell when the series returns this fall. Teen Mom OG follows the lives of Amber, Catelynn and Maci who were featured on the first season of 16 and Pregnant; it documents their first years of motherhood and the strain on family and romantic relationships.