An evaluation of preterm kidney size and function over the first two years of life

BACKGROUND: We carried out a study to determine the impact of prematurity on kidney development in the first 2 years of life. METHODS: In this prospective study, extremely preterm neonates (gestation < 28 weeks) were recruited and underwent assessments at 6, 12, and 24 months of age. A cohort of neonates born term were also recruited and followed up for 24 months. The primary outcomes measured in this study were total kidney volume (TKV) and estimated glomerular filtration rate (eGFR); albuminuria and blood pressure measurements (all provided as mean (standard deviation)) were the secondary outcomes. RESULTS: Fifty-three premature and 31 term neonates (control) were recruited. At the age of 24 months (corrected age), infants born preterm had significantly smaller TKV (56.1 (9.4) vs. 64.8 (10.2) mL; P = 0.006). There was no difference in eGFR. These preterm infants were smaller (11.25 (1.53) vs. 12.9 (1.8) kg; P = 0.002) and shorter (83.8 (3.0) vs. 86.3 (3.4) cm; P = 0.02) when compared with the control group. At 6, 12, and 18 months respectively, preterm infants had, relative to their height, significantly smaller kidney volumes (0.54 (0.1) vs. 0.59 (0.1) mL/cm, P = 0.05; 0.61 (0.1) vs.0.71 (0.1) mL/cm, P = 0.003; and 0.67 (0.1) vs.0.76 (0.1) mL/cm, P = 0.006). CONCLUSIONS: Relative to body length, TKV in premature infants is smaller. Since length reflects adult body proportions more accurately than BSA, TKV to height ratio may be a more important measure in the child. Despite smaller TKV (and therefore fewer nephrons), infants born prematurely achieve similar eGFRs in the first 24 months of life, probably due to single-nephron hyperfiltration.