Kidney development in the first year of life in small-for-gestational-age preterm infants

Background: Small-for-gestational-age (SGA) infants have been reported to have a significantly reduced number of nephrons that could be a risk factor for development of hypertension later in life. Objective: To evaluate kidney size prospectively in relation to other anthropometric parameters during the first year of life in SGA babies. Materials and methods: The babies in the study were 31-36 weeks' gestational age (GA) at birth and were matched with control preterm infants of similar GA, but appropriate for gestational age (AGA). The SGA infants were further classified as symmetrical and asymmetrical according to the anthropometric parameters. Results: The total number of measurements in symmetrical SGA preterm infants was 324, in asymmetrical SGA preterm infants 295, and in AGA infants 536. In symmetrical SGA preterm infants (31-36 weeks' GA) mean kidney length (+/- SD) of 56 +/- 4 mm was significantly different from the controls (58.9 +/- 4.6 mm) up to 6 months' chronological age (P < 0.05). In the asymmetrical SGA preterm infants, mean kidney length (45.3 +/- 4.0 mm) was significantly different from the controls (48.2 +/- 4.4 mm) up to 40 weeks' corrected age. At 1 year chronological age, all preterm infants (symmetrical and asymmetrical SGA and AGA) had similar mean kidney length (61.6 +/- 4.6, 62.8 +/- 4.3, and 62.3 +/- 4.0 mm, respectively). The ratio of kidney length to crown-to-heel length was similar in all preterm groups. Conclusions: Kidney length in preterm SGA infants (symmetrical and asymmetrical) follows closely the other auxological parameters during the first year of life.