Cystatin C in healthy women at term pregnancy and in their infant newborns: Relationship between maternal and neonatal serum levels and reference values

Human cystatin C, a basic low molecular mass protein with 120 amino acid re sidues, is freely filtered by the glomerulus and almost completely reabsorb ed and catabolized by the proximal tubular cells. Cystatin C has been recen tly proposed as a new sensitive endogenous serum marker for the early asses sment of changes in the glomerular filtration rate. To define a reference b asis for future clinical investigations in the perinatal period, we investi gated the relationship between maternal and neonatal serum cystatin C in co mparison with that of creatinine. We also defined reference values in healt hy women at fu Ii-term pregnancy and in full-term newborns over the first 5 days of life. Seventy-eight women with uncomplicated pregnancy, aged betwe en 19 and 40 years, and their infant newborns (43 males, 35 females) were e nrolled in the study. The gestational age ranged from 37 to 43 weeks, and t he birth weight from 2.50 to 4.15 kg. Blood samples were taken from all the women immediately before delivery and from their newborns at birth, 72 and 96 h after birth. Maternal and neonatal renal function was evaluated by st andards parameters and by calculating creatinine clearance. In all serum sa mples, we measured cystatin C, creatinine, and urea. At term gestation, ser um cystatin C ranged from 0.64 to 2.30 mg/L. At birth, serum cystatin C val ues ranged from 1.17 to 3.06 mg/L, significantly decreasing after 3 and 5 d ays of life. No correlation was found between maternal and neonatal serum c ystatin C values (r = 0.09). As cystatin C serum levels in newborns are not significantly correlated with the respective maternal levels, neonatal ser um cystatin C may originate almost exclusively in the neonate.