Single awakening salivary measurements provide reliable estimates of morning cortisol levels in pregnant women

Mood disorders during pregnancy have been associated with adverse effects on maternal as well as fetal health. Since mood, anxiety, and stress disorders are related with elevated cortisol levels, salivary cortisol may be a useful biomarker. Although multiple samples are generally recommended, a single measurement of awakening salivary cortisol could be a simpler and more cost-effective method to determine whether women have elevated morning cortisol levels during a specific period of pregnancy. Therefore, the aim of this validation study among 177 women in the PRIDE Study was to examine whether one awakening salivary cortisol measurement will suffice to classify pregnant women as having normal or elevated cortisol levels compared to awakening salivary cortisol measurements on three consecutive working days. We calculated intraclass correlation coefficients (ICC) and Cohen's kappa statistics (κ) overall as well as in sub-analyses within strata based on maternal age, level of education, net household income, pre-pregnancy BMI, parity, complications during pregnancy, caffeine consumption, gestational week of sampling, and awakening time. The mean cortisol concentrations were 8.98ng/ml (SD 5.32) for day one, 8.62ng/ml (SD 4.55) for day two, and 8.39ng/ml (SD 4.58) for day three. The overall ICC was 0.86 (95% CI 0.82-0.89) while the κ was 0.75 (95% CI 0.64-0.86). For the ICCs calculated within sub-analyses, a maximum difference of 0.11 was observed between the strata. For the κ statistics, most strata did not differ more than 0.12, except for pre-pregnancy BMI, severe nausea, and extreme fatigue with differences up to 0.22. In conclusion, one awakening salivary cortisol measurement is as reliable for the classification of pregnant women into normal and elevated morning cortisol levels as salivary cortisol measurements on three consecutive working days.