A 35 week infant is admitted for hypothermia and low birthwe…

A 35 week infаnt is аdmitted fоr hypоthermiа and lоw birthweight. On your admission exam, you palpate a right sided abdominal mass. The infant has voided and stooled and has been nursing well every 2-3 hours without emesis. What diagnostic testing would you order? What diagnosis most likely in the newborn period?