Sonographic assessment of normal kidney dimensions in the first year of life--a study of 992 healthy infants.

The omission of standards for renal length in infants younger than 1 year may result in a statistically significant increase in the frequency of "spurious" nephromegaly. Nonetheless, there are only a few reports specifically dealing with normal kidney dimensions in infants. Based on sonographic assessments performed on a sample of 992 healthy infants, between January 2002 and December 2004, this paper sets up standards for normal kidney dimensions in children aged 0-3 months, 3-6 months, 6-9 months, and 9-12 months and establishes correlations between kidney dimensions (length, width, and volume) and body length and weight. Linear as well as non-linear nomograms, with percentiles for all the kidney variables examined, based on body length, are provided. Also, statistically significant differences in mean values (P=0.000) for all the observed neonatal kidney parameters, depending on gestational age at birth, are demonstrated. Principal advantages of our nomograms are that they are based on a large number of examined healthy infants and that kidney dimensions are related to body length. In addition, subjects are divided into four sub-annual age groups demonstrating gender-related differences in renal growth dynamics. Our linear nomograms are easier to use for routine clinical practice, but the percentile-based non-linear nomograms we present cover a much wider range of variations in normal infant kidney dimensions.