Low birthweight is associated with lower glomerular filtration rate in middle-aged mainly healthy women

Background. Low birthweight (LBW) has been shown to increase the risk of severe kidney disease. Studies have also shown associations between LBW and lower estimated glomerular filtration rate (GFR) in young adults. In this study we investigated whether LBW associates with measured GFR (mGFR) in middle-aged mainly healthy adults. Methods. We invited individuals with LBW (1100-2300 g) and individuals with normal BW (NBW; 3500-4000 g) ages 41-52 years. GFR was measured using plasma clearance of iohexol. BW and BW for gestational age (BWGA) were obtained from the Medical Birth Registry of Norway and tested as main predictors. GFR was the main outcome. Results. We included 105 individuals (57 LBW and 48 NBW). The mean GFR was 95 +/- 14 mL/min/1.73 m(2) in the LBW group and 100 +/- 13 mL/min/1.73 m(2) in the NBW group (P = 0.04). There was a significant sex difference: in women the mean GFR was 90 +/- 12 versus 101 +/- 14 mL/min/1.73 m(2) in the LBW and NBW groups, respectively (P = 0.006), whereas corresponding values for men were 101 +/- 15 versus 100 +/- 11 mL/min/1.73 m(2) (P = 0.7). Using linear regression, we found the GFR was 4.5 mL/min/1.73 m(2) higher per 1 kg higher BW for women (P = 0.02), with a non-significant 1.2 mL/min/1.73 m(2) lower GFR for men (P = 0.6). In analyses of BWGA, there was also a significant association for women, but not for men. Conclusions. Middle-aged mainly healthy women with LBW had lower mGFR as compared with women with NBW. No such difference was found for men.