Relationships between hydration biomarkers and total fluid intake in pregnant and lactating women

Abstract

Introduction: Previous research established significant relationships between total fluid intake (TFI) and urinary biomarkers of the hydration process in free-living males and females; however, the nature of this relationship is not known for pregnant (PREG) and lactating (LACT) women. Purpose: To determine the relationship between urinary and hematological hydration biomarkers with TFI in PREG and LACT. Methods: Eighteen PREG/LACT (age: 31 ± 3 years, pre-pregnancy BMI: 24.26 ± 5.85 kg m−2) collected 24-h urine samples, recorded TFI, and provided a blood sample at 5 time points (15 ± 2, 26 ± 1, 37 ± 1 weeks gestation, 3 ± 1 and 9 ± 1 weeks postpartum during lactation); 18 pair-matched non-pregnant (NP), non-lactating (NL) women (age: 29 ± 4 years, BMI: 24.1 ± 3.7 kg m−2) provided samples at similar time intervals. Twenty-four-hour urine volume (UVOL), osmolality (UOSM), specific gravity (USG), and color (UCOL) were measured. Hematocrit, serum osmolality (SOSM), and serum total protein (STP) were measured in blood. Results: Significant relationships were present between TFI and urinary biomarkers in all women (P < 0.004); these relationships were not different between PREG and NP, and LACT and NL, except UVOL in PREG (P = 0.0017). No significant relationships between TFI and hematological biomarkers existed (P > 0.05). Conclusion: Urinary biomarkers of hydration, but not hematological biomarkers, have a strong relationship with TFI in PREG, LACT, NP, and NL women. These data suggest that urinary biomarkers of hydration reflect TFI during pregnancy and breast-feeding.