Mapping of Determinants of Urinary Sex Steroid Metabolites During Late Pregnancy: Results from Two Spanish Cohorts

(1) Background: Steroid hormones (SH), including sex steroids and corticosteroids, are crucial for a healthy pregnancy. We identified and replicated the main determinants associated with a wide range of SH molecular features during later pregnancy. (2) Methods: We analyzed urinary SH metabolites in 1,221 pregnant women (aged 28 to 37 years) in the 3rd trimester from two cohorts: BiSC (2018-2021, n=721) and INMA-Sabadell (2004-2006, n=500). Using targeted UHPLC-MS/MS, we quantified 50 SH metabolites, resulting in 13 hormone groups, 9 sulfate/glucuronide (S/G) ratios, and 17 estimated steroid enzymatic activities across steroidogenesis pathways including progestogens, androgens, estrogens and corticosteroids metabolites. In total 89 SH molecular features were considered in the study. We applied Elastic Net Regression to identify determinants, and multivariable linear regression models to estimate variance explained (3) Results: Pregnant women with gestational age at sample collection of BiSC: 34.7 (SD 1.5) and INMA-Sabadell 34.3 (SD 1.6) gestational weeks were considered in the study. Among the 47 and 28 determinants from BiSC and INMA-Sabadell, respectively, 10 determinant-SH metabolome pairs showed statistically significant associations (P< 0.05) and were concordant in most cases in effect direction across the cohorts. Maternal BMI was the most influential predictor, accounting for 38% of the all associations, followed by maternal age (25%), maternal ethnicity (11%), physical activity (7%), smoking (5%), parity (4%), sex of the fetus (4%), dietary fat intake (4%), sleep (2%), and alcohol intake (2%). (4) Conclusions: Our findings provide evidence that clinical, lifestyle and sociodemographic factors shape the maternal SH metabolome during late pregnancy.