In general, 12mm of hydronephrosis in the right kidney of a newborn baby is a relatively normal phenomenon, but the specific situation varies from person to person.
Hydronephrosis is mainly due to one or both sides of the body of the ureter or urethra obstruction, resulting in urine can not be normal metabolism through the kidneys to the bladder, the accumulation of urine in the kidneys continue to accumulate, and thus formed. In general, it is relatively normal for newborns to develop hydronephrosis.
Neonatal hydronephrosis of about 12mm is a less serious condition, for some good health can be cured by themselves, but individual differences are large, so you need to pay close attention to the changes in the condition, if there are bladder irritation signs, lower back and abdominal pain and other symptoms, it is recommended that immediate medical attention, in order to prevent further deterioration of the condition leading to kidney damage.