The neonatal kidney achieves concentrating ability equivalent to adult\'s kidney by –
"Normal adult kidney can produce urine with an osmolality of greater than 1000 m Osm/kg water The healthy newborn infant, subject to water deprivation for 10-14 hours can achieve an osmolality of only 500-700 m Osm /kg. This value increases gradually during the first few months and approximates to the adult value by about one year of age."
On the other hand, the newborn can dilute his urine to a minimum of 50 m Osm/kg much like an older child.
One year of age
Eighteen months of age
Three to six months of age
Just before puberty