Background: Urine osmolality (UOSM) reflects the renal regulation of excess fluid or deficit fluid, and therefore, serves as a marker of hydration status. Little is known about monitoring hydration in pregnant and lactating women despite significant physiological challenges to body water balance during that time. Therefore, we designed a study to assess if urine color (UCOL), an inexpensive and practical method, was a valid means of assessing urine concentration. Twenty-four hour UCOL was significantly correlated with 24 h UOSM in all women: pregnant, lactating, and control (r = 0.61-0.84, all p < 0.001). Utilizing a receiver operating characteristic statistical analysis, we found that 24 h and single sample UCOL had excellent diagnostic accuracy for identifying UOSM ≥500 mOsm·kg-1 in all women (area under the curve = 0.68-0.95, p < 0.001-0.46), and the UCOL that reflected this cut off was ≥4 on the UCOL chart. Summary: Therefore, UCOL is a valid marker of urine concentration and ultimately hydration status in pregnant, lactating, and non-pregnant, non-lactating women. For pregnant, lactating, and control women, the UCOL chart is a valid tool that can be used to monitor urine concentration in a single sample or over the course of the day via a 24 h sample. Key Message: Women who present with a UCOL of 4 or more likely have a UOSM ≥500 mOsm·kg-1. Given the positive health benefits associated with UOSM <500 mOsm·kg-1, women should aim for a 1, 2, or 3 on the UCOL chart. If a UCOL of ≥4 is observed, women should consider increasing fluid consumption to improve hydration status.
Urine color as an indicator of urine concentration in pregnant and lactating women
