Comparing ambulatory spot urine protein/creatinine ratios and 24-h urine protein measurements in normal pregnancies.

OBJECTIVE: To determine whether a single specimen protein/creatinine ratio correlated with a 24-h urine protein measurement in ambulatory women with normal pregnancies. METHODS: A prospective cohort was evaluated of healthy women performing a 24-h urine collection and spot urine measurement for protein and creatinine in each trimester and the postpartum period. Data were analyzed to establish the correlation of values and the reliability of cut-off values. RESULTS: Fifty-eight women were enrolled in the study. Thirty-three completed at least one measurement. Three (5.1%) developed pre-eclampsia. With the use of linear regression, the spot protein/creatinine ratio correlated with the 24-h protein measurement in the first trimester and postpartum periods only (p < 0.001 and p < 0.043, respectively). It did not correlate in the second or third trimester (p = 0.637 and p = 0.290, respectively). CONCLUSION: In this population, the protein/creatinine ratio correlated only with the 24-h urine protein measurement in the first trimester and postpartum periods. In the periods of pregnancy where physiological changes are most prevalent, the ratio does not predict total urinary protein reliably.