Objective: To assess whether creatinine excretion alters in human preg
nancy. Methods: Longitudinal study of 24-h urinary excretion of creati
nine during human pregnancy. Main Outcome Measures. Relative creatinin
e excretion as pregnancy advanced. Results: Twenty-four-hour creatinin
e excretion remained relatively constant as pregnancy advanced. Conclu
sions: Creatinine excretion can be used with confidence during pregnan
cy for estimation of completeness of collection in examination of 24-h
excretion of other metabolites.