Unborn baby has enlarged kidneys on scan. What to do next?

Pre or postnatal US? Kidneys are occasionally generous in their size on a prenatal ultrasound and revert to normal by 2 wks. When this is detected in pregnancy, i generally do another study @ 2 wks if i will be following the child or after birth if they plan to move to another town or dr. A post natal study is more accurate & can define more precisely if there are issues like a backup of urine in a ureter.