Association between Maternal Midterm eGFR and Newborn Birth Weight: Seiiku Boshi Cohort Study

Lower maternal midterm eGFR was independently associated with increased risks of low birth weight and small for gestational age. Adding eGFR to conventional risk models improved prediction of adverse birth outcomes, highlighting its value as a prognostic marker. Midterm eGFR assessment may help identify at-risk pregnant women without overt disease, allowing closer monitoring and timely intervention.

Little is known regarding whether renal function during pregnancy among healthy women is associated with pregnancy outcomes. Evidence based on the universal screening of maternal eGFR is lacking. We investigated the association of maternal eGFR during the second trimester with fetal birth weight.

This prospective birth cohort study includes 1666 singleton pregnant women (median age 36 years, median body mass index 20.0) who had universal screening of eGFR during the second trimester. Participants were categorized into the quartile of eGFR. The first quartile group was defined as low eGFR, the fourth quartile group as high eGFR, and the second and third quartile group as reference. The primary outcomes are low birth weight (LBW) and small for gestational age (SGA). Multivariable logistic regression models were used to investigate the association of maternal eGFR and pregnancy outcomes.

As compared with the reference group, the adjusted odds ratios (95% confidence intervals [CIs]) for LBW and SGA in the low eGFR group were 2.25 (1.48 to 3.40) and 2.51 (1.63 to 3.87), respectively, and in the high eGFR group were 0.69 (0.40 to 1.19) and 0.55 (0.30 to 1.02), respectively. The adjusted odds ratios of eGFR per SD decrease (95% CI) for LBW and SGA were 1.92 (1.50 to 2.45; P = 0.013) and 2.07 (1.60 to 2.68; P < 0.001). The prediction models were improved by adding eGFR to the models including covariates for LBW (C statistics difference, +0.018; 95% CI, -0.004 to 0.040, net reclassification improvement;, 0.377; 95% CI, 0.208 to 0.545, and integrated discrimination improvement, 0.0135; 95% CI, 0.005 to 0.022) and for SGA (C statistics difference, +0.041; 95% CI, 0.003 to 0.080; net reclassification improvement, 0.408; 95% CI, 0.226 to 0.591; and integrated discrimination improvement, 0.017; 95% CI, 0.009 to 0.025).

The lower maternal midterm eGFR is associated with LBW and SGA, while the higher eGFR is not. Evaluating midterm eGFR may help identify healthy women at risk of adverse birth outcomes.