Associations among PM_2.5, corticotropin releasing hormone, estriol, and progesterone in pregnant persons in Puerto Rico

<i>Background.</i> Exposure to PM_2.5 is associated with adverse birth outcomes and early development. Pregnancy is typically characterized by the production of several important hormones that impact aspects of maternal and fetal physiology, including progesterone, estriol, and corticotropin releasing hormone (CRH). No previous studies have examined PM associations in pregnant persons for CRH and estriol. <i>Methods.</i> We used linear mixed effects models to investigate associations between PM_2.5 and pregnancy hormones in 1,041 pregnant persons ages 18-41 living in Puerto Rico between 2011 and 2020. Individual 3-, 7-, and 30-day moving average exposures were assigned from EPA data sources. Hormone levels were analyzed in blood collected at study visits at 16-20 and 20-24 weeks of gestation. Models were adjusted for demographics, socioeconomic status, and health behaviors.<i>Results.</i> Mean participant exposures for 3-, 7-, and 30-day PM_2.5 were 8.0 ± 5.9, 8.2 ± 5.3, and 8.1 ± 4.4 μg m^-3. In base models, increased PM_2.5 exposure was associated with lower levels of progesterone, CRH, and estriol. In adjusted models, 10 μg m^-3 increase in PM_2.5 was associated with 11.2% (95% CI: 17.6, 4.3; p = 0.003) and 14.9% (95% CI: 23.4, 5.4; p = 0.004) lower CRH for 7-day and 30-day exposures. In cross-sectional models, the inverse CRH association was driven by the 20-24 week gestation period with a 12.4% reduction (95% CI: 21.8, 1.9; p = 0.022) for 7-day and 17.5% reduction (95% CI: 29.7, 3.0; p = 0.020) for 30-day exposure. Other investigated associations were null.<i>Conclusions.</i> In pregnant persons in Puerto Rico, we observed that elevated PM_2.5 exposures were significantly associated with decrements in CRH, but not in other pregnancy-associated hormones. CRH may be an important pathway through which prenatal PM_2.5 impacts normal pregnancy.