Salivary estradiol and progesterone across the menstrual cycle: Association and agreement with serum concentrations

Saliva provides a noninvasive alternative to serum for serial sampling of estradiol and progesterone. This study examined salivary estradiol and progesterone patterns and the relationship between salivary and serum estradiol, progesterone, and the estradiol to progesterone ratio (E2:P) across the menstrual cycle (MC) in physically active females. Saliva was collected daily from females over one or two MCs, with blood collected five times across two MCs. At-home ovulation tests and a retroactive serum progesterone (≥5 ng·mL^-1) identified ovulation. Salivary estradiol and progesterone profiles followed expected serum patterns. Repeated measures correlations (r_rm) showed strong significant associations between salivary and serum progesterone (r_rm = 0.58, p < 0.001) and salivary and serum E2:P (r_rm = 0.57, p < 0.001), but not salivary and serum estradiol (p = 0.09). No associations emerged in MCs with serum progesterone <5 ng·mL^-1. Linear mixed models confirmed positive associations for serum and salivary progesterone (β = 0.02, p < 0.001) and E2:P (β = 9.44, p < 0.001). Bland-Altman analyses indicated poor agreement between salivary and serum concentrations. Although saliva does not directly replace serum measures, it may better reflect the biologically active hormone fraction and offers a practical tool for tracking hormonal patterns.