Chronic kidney disease associated with extremely premature birth and extremely low birth weight may progress through the burden of growth.

Chronic kidney disease associated with low birth weight and/or premature birth (L/P-CKD) in infants may result from a decreased number of nephrons at birth. These infants may develop acute kidney injury due to exposure to nephrotoxic substances or other events during nephrogenesis in early infancy. Nonetheless, L/P-CKD progression remains unclear. We present three cases of L/P-CKD diagnosed after neonatal intensive care unit (NICU) discharge. Three patients were born extremely prematurely (gestational age, 24-26 weeks) with extremely low birth weight (606-906 g). They were admitted to the NICU (117-311 days) anad received several nephrotoxic medications during the early postnatal period. They showed elevated serum creatinine levels at 4 weeks after birth, which decreased to normal levels at NICU discharge. Proteinuria was first detected during adolescence (10-15 years) on annual school urine screening, with a remarkable increase in their height (18 - 50.8 cm), without known episodes of urinary tract infection, dehydration, lifestyle-related issues, such as excessive salt/protein intake, and extreme lack of exercise that might have caused kidney damage. Their kidneys were smaller than normal on renal ultrasonography. Open renal biopsy findings indicated glomerulomegaly and perihilar glomerulosclerosis in two of the three patients, suggesting glomerular hypertension. The remarkable differences between the body height before CKD and the timing of diagnosis of CKD could contribute to the progress of CKD. Long-term follow-up of low birth weight and extremely premature infants, from NICU discharge until adulthood, should be established.