['This study aims to determine the effect of pregnancy on the accuracy of 3 commonly used methods to estimate glomerular filtration rate ([GFR] creatinine clearance, the Cockroft-Gault, and modification of diet in renal disease [MDRD] formulas) using the inulin clearance as a reference.', 'Longitudinal study design.', 'University hospital.', 'A total of 44 parous nonsmoking Caucasian women. They had a history of uneventful pregnancy (n = 9), preeclampsia (n = 27), and intrauterine fetal demise (n = 8).', 'Measurements were performed both in pre-pregnancy and early pregnancy (8 weeks of gestation) and included inulin infusion, blood pressure, and 24-hour urinary and serum creatinine. Agreement between methods to estimate GFR was assessed by the Bland and Altman method.', 'GFR estimated by inulin and creatinine clearances and the Cockroft-Gault and MDRD formulas.', 'During early pregnancy, the GFR measured by inulin increased 32% compared with the pre-pregnant value (from 115 ± 18 to 150 ± 23 mL/min·1.73 m(-2)), whilst the GFR measured by the indirect methods only increased 20%. The observed bias and limits of agreements are larger in early pregnancy relative to the pre-pregnant state for all 3 methods.'] Does pregnancy reduce the accuracy of the estimated glomerular filtration rate based on Cockroft-Gault and MDRD formulas?