Urine color as an indicator of urine concentration in pregnant and lactating women

Aim: Urine concentration measured via osmolality (U_OSM) and specific gravity (U_SG) reflects the adequacy of daily fluid intake, which has important relationships to health in pregnant (PREG) and lactating (LACT) women. Urine color (U_COL) may be a practical, surrogate marker for whole-body hydration status. Purpose: To determine whether U_COL was a valid measure of urine concentration in PREG and LACT, and pair-matched non-pregnant, non-lactating control women (CON). Methods: Eighteen PREG/LACT (age 31 ± 1 years, pre-pregnancy BMI 24.3 ± 5.9 kg m⁻²) and eighteen CON (age 29 ± 4 years, BMI 24.1 ± 3.7 kg m⁻²) collected 24-h and single-urine samples on specified daily voids at five time points (15 ± 2, 26 ± 1, and 37 ± 1 weeks gestation, 3 ± 1 and 9 ± 1 weeks postpartum during lactation; CON visits were separated by similar time intervals) for measurement of 24-h U_OSM, U_SG, and U_COL and single-sample U_OSM and U_COL. Results: Twenty-four-hour U_COL was significantly correlated with 24-h U_OSM (r = 0.6085–0.8390, P < 0.0001) and 24-h U_SG (r = 0.6213–0.8985, P < 0.0001) in all groups. A 24-h U_COL ≥ 4 (AUC = 0.6848–0.9513, P < 0.05) and single-sample U_COL ≥ 4 (AUC = 0.9094–0.9216, P < 0.0001) indicated 24-h U_OSM ≥ 500 mOsm kg⁻¹ (representing inadequate fluid intake) in PREG, LACT, and CON. Conclusions: Urine color was a valid marker of urine concentration in all groups. Thus, PREG, LACT, and CON can utilize U_COL to monitor their daily fluid balance. Women who present with a U_COL ≥ 4 likely have a U_OSM ≥ 500 mOsm kg⁻¹ and should increase fluid consumption to improve overall hydration status.