Fetal renal maturation. Studies on urinary beta 2 microglobulin the neonate

Beta 2 microglobulin [B2m] and creatinine [Cr] concentrations were measure in the urine of 27 newborn infants. At birth, urinary [B2m] and [B2m]/[Cr] ratios were significantly lower in infants born beyond 36 weeks' gestation. Serial measurements, postnatally, showed a progressive decrease in the urine [B2m]/[Cr] ratio of infants born prematurely. These findings suggest an increase in tubular uptake of B2m with increasing gestational and postnatal age. The current findings tend to support the hypothesis that the decrease in [B2m] observed in amniotic fluid beginning at approximately 36 weeks' gestation reflects maturation of fetal proximal renal tubular function.