By Lisa Rapaport (Reuters Health) – – Even though doctors often tell parents that newborns will regain weight lost after birth within a week or two, many infants take much longer to achieve this milestone, a U.S. study suggests. Nearly all newborns lose weight during the first days after birth, regardless of whether they are breastfed or formula fed. Many doctors expect babies to regain those lost ounces and surpass their birth weight within 10 to 14 days.