Britney Spears has become an aunt--her teenage sister Jamie Lynn has given birth to a baby girl. The Zoey 101 actress, 17, is reported to have checked into the Mississippi Southwest Regional Medical Center in McComb, Mississippi, at 4 a.m. local time on Thursday, where she welcomed the unnamed tot, according to The National Enquirer. And Britney was on hand to help--she was photographed arriving at the hospital early that morning. The baby is Jamie Lynn and her fiancé Casey Aldridge's firstborn. The teen star stunned the Spears family when she announced her pregnancy news last year, at the age of 16.