Pregnant Nicole Richie has checked into jail to begin a four-day sentence after pleading guilty to driving under the influence. The socialite was charged with a misdemeanor DUI in Los Angeles on 27 July (07), when she was handed a prison term, a fine and 36 months of summary probation. The Simple Life star was told she had to report to the Central Regional Facility in Lynwood, California before 28 September (07). Details about her arrival at the prison were kept top secret in an effort to avoid a media frenzy, but U.S. TV show Entertainment Tonight is reporting that Richie started her jail term on Thursday afternoon (23Aug07). Richie was arrested on 11 December (06) when she was found driving her Mercedez Benz the wrong way down California State Route 134 highway in Burbank. After failing an on-field sobriety test, Richie admitted to having smoked marijuana and taking a vicodin painkiller. Richie is five months pregnant with rocker boyfriend Joel Madden's baby.