[Development of renal function in low and extremely low birth weight infants: correlation with gestational and postnatal age].

The postnatal development of renal function was compared in 29 infants with a gestation age (GA) of 26-30 weeks mean 28.5 680-1,450 g means 1080 g and in 31 infants with a gestation age of 31-33-weeks, means 31.5, 950-2000 g means 1580 g. Observation were made during the 1st, 5th and 10th day. From 1st to 10th day the creatinine clearance increased but it was significantly lower in GA 26-30 that in GA 31-33. During the first 10 days of life diuresis was lower in GA 26-30 that in GA 31-33 but thereafter was the same in both groups. Urinary sodium excretion was high at 1st and 5th day in both groups and decreased with increasing postnatal age. Na excretion was slightly higher in GA 26-30 that in GA 31-33 at 1st and 5th day but not at 10th day. UK/UNa was below 1 in both groups during the 1st, 5th day and increased with postnatal age. FeNa% was high in both groups but in GA 26-30 was significantly hither then in GA 31-33. We conclude that the postnatal development of renal function is retarded in all preterm infants and is slightly slower in infants with a GA below 31 weeks than in infants with GA 31-33 weeks.