POSTNATAL DEVELOPMENT OF RENAL FUNCTION IN PRE‐TERM AND FULL‐TERM INFANTS

Abstract

This study was designed to examine the effect of gestational age (GA) on the postnatal development of renal function and was performed in pre-term (PT) infants (GA = 30-34 wk) and in full-term (FT) infants (GA = 39-41 wk). Postnatal age ranged from 1-35 days. From 8 h urine samples collected after spontaneous voiding and a capillary blood sample, determinations was made of the clearance of creatinine (CCr), the fractional excretion of .beta.2-microglobulin (FE.beta.2) and the fractional excretion of Na (FENa). In some infants receiving fluid parenterally, simultaneous determinations were made of the clearance of creatinine and inulin. As judged from this study, CCr is a reliable indicator of the glomerular filtration rate (GFR). GFR was almost the same in newborn PT and FT but from 0.3-1 wk of age GFR increased significantly more rapidly in FT than in PT. From 1-5 wk of age GFR increased at approximately the same rate in PT and FT infants. The absolute value for GFR in 3-5 wk old infants was lower in PT than in FT. FE.beta.2 was higher in PT than in FT infants during the entire 1st month of life and FENa was higher in PT than in FT infants during the 1st week of life, suggesting a glomerular tubular imbalance at least at the level of the proximal tubule in PT infants. Different stages of maturation will alter the preconditions for the renal adaptation to extrauterine life during at least the 1st month of life. Special attention must be paid to the limited renal function in PT during their entire 1st month of life.