Growth Restriction at Birth and Kidney Function During Childhood

Background: Individuals born small for gestational age (SGA) are at risk of developing hypertension and kidney disease later in life. The time that this may occur is unknown. This study aims to examine kidney function in preschool children who were SGA. Study Design: A case-control study. Settings & Participants: The study included 100 children, 60 SGA and 40 appropriate-for-gestational-age (AGA) controls matched with the SGA children according to birth characteristics (gestational age and sex) and characteristics at the time of the study (body weight, body height, body mass index, and age). SGA children were classified according to severity of growth restriction into 2 groups: birth weight less than the 3rd percentile (n = 25) and birth weight from the 3rd to 10th percentile (n = 35). Predictors: Being SGA and severity of growth restriction at birth. Outcomes & Measurements: Kidney function was estimated at a mean age of 5 years by using serum creatinine level; estimated glomerular filtration rate; urinary albumin excretion; fractional excretion of sodium, potassium, phosphate, magnesium, and uric acid; transtubular potassium gradient; and urinary calcium-creatinine ratio calculated from 3-hour urine collections. Blood pressure and kidney length also were measured. Results: Kidney length, serum creatinine level, and estimated glomerular filtration rate did not differ among the 3 groups. Systolic and diastolic blood pressures were greater in SGA children with birth weight less than the third centile versus controls (107.5 +/- 11 versus 102 +/- 10 mm Hg [P = 0.03] and 69 +/- 7.5 versus 65 +/- 8.6 mm Hg [P = 0.02] for systolic and diastolic blood pressure, respectively). Both groups of SGA children had greater urinary calcium excretion than AGA children (urinary calcium-creatinine ratio, 0.16 +/- 0.08 and 0.16 +/- 0.10 in SGA with birth weight < 3rd and 3rd to 10th percentiles versus 0.10 +/- 0.09 in AGA; P = 0.04 and P = 0.03, respectively). SGA children also had lower uric acid excretion despite greater serum uric acid levels (fractional excretion of uric acid, 7.4% +/- 4% and 6.9% +/- 5% versus 10.5% +/- 5.9%; P = 0.02 and P = 0.003, respectively). Limitations: Relatively small sample size, blood pressure was measured on a single visit. Conclusions: Children born SGA showed alterations in calcium and uric acid urinary excretion at preschool age, and blood pressure was related to the severity of growth restriction. Am J Kidney Dis 54:850-858. (C) 2009 by the National Kidney Foundation, Inc.