Palin Biography: Her Secret Pregnancy, Eldest Daughter Bristol Was Living Outside The House

03/19/2009 05:12 am ET | Updated May 25, 2011

A new biography of Alaska Gov. Sarah Palin reveals that her secret pregnancy with son Trig was nearly uncovered when one of her daughters discovered Trig's prenatal ultrasound scan and confronted Palin with the picture.

"Sarah made one slip-up -- but [she] dampened suspicion by explaining it away," reports Trailblazer: An Intimate Biography of Sarah Palin, by PEOPLE Assistant Editor Lorenzo Benet and being published Tuesday by Simon & Schuster's Threshold Editions.