Latent trait cortisol (LTC) during pregnancy: Composition, continuity, change, and concomitants.

Area of Science:

• Endocrinology
• Psychoneuroendocrinology
• Human Physiology

Background:

• Individual differences in hypothalamic pituitary adrenal (HPA) axis activity are typically measured using summary cortisol levels.
• These summary measures are often assumed to reflect stable, trait-like individual differences.
• A novel latent variable approach, latent trait cortisol (LTC), offers a new method to assess HPA axis function.

Purpose of the Study:

• To extend the understanding of latent trait cortisol (LTC) as a measure of trait-like HPA axis function during pregnancy.
• To evaluate the validity and stability of LTC models during the course of pregnancy.
• To investigate the relationship between LTC and other diurnal cortisol parameters.

Main Methods:

• Prospective collection of 8 diurnal saliva samples (4 samples/day, 2 days) from 380 pregnant women across three trimesters.
• Assay of saliva samples for cortisol levels.
• Application of confirmatory factor analysis to fit LTC models to early morning and daytime cortisol data.

Main Results:

• Daytime LTC models demonstrated adequate fit for individual trimester data.
• These daytime LTC models exhibited strong correlations between trimesters, indicating stability throughout pregnancy.
• Daytime LTC was uncorrelated with the cortisol awakening response and daytime slope but strongly correlated with the area under the curve from ground.

Conclusions:

• The findings support the validity of latent trait cortisol (LTC) as a robust measure of cortisol during pregnancy.
• Daytime LTC appears to be a stable trait measure, not significantly influenced by pregnancy-induced alterations in HPA axis function.
• LTC provides a promising approach for assessing stable HPA axis function in pregnant populations.