Evaluating Allopregnanolone as a Potential Mediator of Prenatal Psychosocial Distress and Birth Outcomes in the Healthy Start Cohort

Background: Prenatal psychosocial distress is a risk factor for adverse birth outcomes such as preterm birth, but the biological pathways remain incompletely understood. Allopregnanolone (ALLO), a stress-responsive, progesterone-derived neuroactive steroid, may contribute to pregnancy maintenance by inhibiting uterine activation and modulating inflammatory and neuroendocrine pathways involved in parturition. Few human studies have examined ALLO during pregnancy in relation to birth timing and related outcomes, and no study to our knowledge has examined the entire pathway of prenatal psychosocial distress, ALLO, and birth outcomes. Here, we evaluated whether maternal ALLO concentrations and the ALLO-to-progesterone ratio mediate associations between prenatal psychosocial distress and birth outcomes. Methods: This study included 237 pregnant participants from the Healthy Start Cohort, enriched for psychosocial distress (n=57 high-distress; n=180 low-distress) assessed using the Edinburgh Perinatal Depression Scale (EPDS) and EPDS-3A anxiety subscale. We measured maternal serum ALLO and related steroid hormones at approximately 17 and 27 weeks gestation (range: 10-34 weeks) using a validated HPLC-MS/MS assay and evaluated natural log (ln)-transformed ALLO and the ALLO-to-progesterone ratio as potential mediators. The primary outcome was gestational age at birth; secondary outcomes included birthweight-for-gestational-age z-score (BW/GA), percent fat mass (%FM), and birth length-for-gestational-age z-score (BL/GA). We conducted regression-based mediation analyses by comparing the total and direct effects of prenatal psychosocial distress after adjustment for each proposed mediator. Results: Participants had a mean +- SD age of 29+-6 years; 38% were nulliparous, and 60% identified as non-Hispanic White. Of the birth outcomes assessed, prenatal psychosocial distress was only associated with BL/GA ({beta} = -0.49; 95% CI: -0.84, -0.14). Adjustment for ALLO at ~27 weeks as a mediator minimally attenuated the association between prenatal distress and BL/GA ({beta} = -0.46; 95% CI: -0.81, -0.10, 6.1% attenuation), whereas adjustment for the ALLO-to-progesterone ratio resulted in 20.8% attenuation ({beta} = -0.38; 95% CI: -0.74, -0.03). Conclusions: Maternal prenatal distress was associated with shorter birth length. The ALLO-to-progesterone ratio, but not ALLO itself, may partially mediate this relationship. These findings support neurosteroid metabolism as a biological pathway linking prenatal distress to fetal length accrual. Future mechanistic studies are needed to confirm these findings.