Background Prognostic criteria to inform women with moderate to severe renal insufficiency who wish to bear children are not well established. Study Design Longitudinal multicenter cohort study. Settings & Participants Nondiabetic white women with pregnancies proceeded beyond the 20th week and estimated glomerular filtration rate (GFR) less than 60 mL/min/1.73 m2 (<1 mL/s/1.73 m2 ) before conception. Predictors Baseline GFR and proteinuria (exposure); other clinical characteristics at conception (covariates). Outcomes & Measurements Difference in GFR decreases before conception versus after delivery (mixed linear models); low birth weight (<2,500 g), and maternal renal survival (logistic and Cox regressions). Results 49 women were studied. Mean serum creatinine and GFR at conception were 2.1 ± 1 (SD) mg/dL (186 ± 88 μmol/L) and 35 ± 12 mL/min/1.73 m2 (0.58 ± 0.2 mL/s/1.73 m2 ), respectively. Overall mean GFR after delivery was less than before conception (30 ± 13.8 versus 35 ± 12.2 mL/min/1.73 m2 0.50 ± 0.23 versus 0.58 ± 0.20 mL/s/1.73 m2 ; P < 0.001), but the rate of GFR decrease did not change (0.55 ± 0.8 versus 0.50 ± 0.3 mL/min/mo 0.0092 ± 0.013 versus 0.0083 ± 0.005 mL/s/mo; P = 0.661). Independent of potential confounders, the combined presence of baseline GFR less than 40 mL/min/m2 (<0.67 mL/s/m2 ) and proteinuria with protein greater than 1 g/d, but not either factor alone, predicted faster GFR loss after delivery compared with before conception (1.17 ± 1.23 versus 0.55 ± 0.39 mL/min/mo; difference, 0.62 mL/min/mo; 95% confidence interval CI, 0.27 to 0.96 mL/min/mo 0.020 ± 0.021 versus 0.0092 ± 0.007 mL/s/mo; difference, 0.10 mL/s/mo; 95% CI, 0.005 to 0.016 mL/s/mo). The presence of both risk factors, but not either alone, also predicted shorter time to dialysis therapy or GFR halving (N = 20; hazard ratio, 5.2; 95% CI, 1.7 to 15.9) and low birth weight (N = 29; odds ratio, 5.1; 95% CI, 1.03 to 25.6). Limitations Generalizability to other settings; study power. Conclusion In women with renal insufficiency, the presence of both GFR less than 40 mL/min/1.73 m2 (<0.67 mL/s/m2 ) and proteinuria with protein greater than 1 g/d before conception predicts poor maternal and fetal outcomes.