Mo504low birth weight associates with smaller kidney size in middle-aged women

Abstract Background and Aims Low birth weight is associated with increased risk of kidney disease due to lower nephron endowment leading to hyperfiltration and subsequent nephron loss. Nephron number is thought to associate with kidney size. We compared kidney size measured by magnetic resonance imaging (MRI) with ultrasonography and measured glomerular filtration rate (mGFR) in adults with normal versus low birth weight. Method Healthy individuals aged 42-52 years with Low birth weight (LBW – 1100-2300g) and normal birth weight (NBW - 3500-4000g) were invited. GFR was measured using plasma clearance of iohexol. Kidney volume was measured on MRI images using axial T2 images and coronal T1 images with fat saturation without contrast enhancement, calculations were performed according to the ellipsoid formula - π/6 x Length x Width x Depth. Ultrasonographic imaging was done using a dorsal approach. In the maximal longitudinal view the parenchymal area was calculated subtracting the area of a manual tracing around the renal pelvis from the area of a manual tracing of the whole kidney. Volume and area from the two kidneys were added and total value was used for analyses. Kidney size measurements were compared between the two groups of LBW vs NBW, and analysis using Pearson’s correlation coefficient R between kidney volume and measured GFR and parenchymal area was performed. Results We included 102 individuals (54 LBW, 48 NBW). Total kidney volume was 302 ± 51 ml for female NBW vs 258 ± 48 ml for female LBW (p=0.002). For men, total kidney volume was 347 ± 51 ml vs 340 ± 65 ml (p=0.7). Measured GFR was significantly associated with kidney volume with R=0.52 (p<0.001) for women and R=0.39 (p=0.007) for men. Kidney parenchymal area measurements using ultrasonography showed similar results with an R=0.77 between the MRI and the ultrasonography measurement and similar differences for sex and birth weight were seen. Conclusion Healthy middle-aged females born with LBW have smaller kidneys than healthy middle-aged females born with NBW, no difference were seen for males. Kidney volume associate with measured GFR.