Birth Weight Is Associated With Kidney Size in Middle-Aged Women

Abstract Background Low birth weight (LBW) is associated with increased risk of kidney disease due to lower nephron endowment leading to hyperfiltration and subsequent nephron loss. Kidney size is commonly used as a proxy for nephron number. We compared kidney volume measured by magnetic resonance imaging (MRI) with measured glomerular filtration rate (mGFR) in adults with either normal or low birth weight. Methods Healthy individuals aged 42-52 years with 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. 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). mGFR was significantly associated with kidney volume with r=0.52 (p Conclusion Healthy females born with LBW have smaller kidneys than healthy females born with NBW. The previously shown associations between LBW and lower mGFR in adult women might be explained by smaller kidney volume.