Abstract Body (Do not enter title and authors here): Introduction
Psychosocial stressors in early pregnancy are associated with a higher risk of adverse pregnancy outcomes (APOs), including hypertensive disorders of pregnancy (HDP), gestational diabetes, and preterm birth. However, the biological pathways underlying these associations are not well delineated. This study aims to investigate proteomic markers that may underlie the association between early pregnancy psychosocial stress and APOs.

Methods
Data were from the Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-to-Be, a prospective study conducted from 2010-13. Participants were selected using a case-control design (508 HDP cases and 1081 controls). An aptamer-based assay was used to quantify 6,894 proteins in blood serum collected at the first-trimester study visit. Psychosocial stress during the month preceding the same visit was defined as a score greater than 13 on the 10-item Perceived Stress Scale. We used linear regression, adjusted for age and gestational age, to estimate the associations between stress and proteomic analytes. We then used logistic regression models to estimate the associations of these analytes with APOs. To identify potential biological pathways, we constructed a knowledge graph integrating Human Phenotype Ontology terms and STRING protein-protein interactions.

Results
Among 1,589 pregnant participants, the mean (SD) age was 27 (6) years and 42% reported psychosocial stress. Heparan sulfate 6-O-sulfotransferase 3 (HS6ST3) was significantly associated with both stress and APOs after FDR correction. Higher psychosocial stress was associated with lower expression of HS6ST3 (-0.27 [95% CI -0.32, -0.22]). Also, a lower expression in HS6ST3 was associated with higher risk of HDP (aOR 0.72 [0.61, 0.85]), gestational diabetes (aOR 0.59 [0.48, 0.71]), and preterm birth (aOR 0.75 [0.61, 0.92]). Proteomic values were expressed in SD units of log2-transformed SomaScan measurements. A knowledge graph was created, which identified close connections between anxiety (phenotype term closest to stress), APOs, and HS6ST3 with shared biological pathways, including GPC* gene clusters, SHH, LYN, and PTCH1 (Figure).

Conclusions
Early pregnancy psychosocial stress was significantly associated with lower HS6ST3 expression and increased risk of APOs. Genes known to interact with HS6ST3, which are involved in neuroimmune signaling, placental development, and vascular function, may represent plausible pathways linking psychosocial stress to APOs.