The oxidative balance score (OBS) serves as a comprehensive measure of exposures related to oxidative stress, considering both dietary antioxidants and lifestyle exposures. There is no evidence regarding the relation between OBS and postpartum depression (PPD). In this study, we aimed to determine the relationship between OBS during pregnancy and PPD. In this cohort study, 243 Iranian pregnant women were recruited using a convenience sampling method from 2022 to 2023. Dietary intakes were obtained using a validated food frequency questionnaire. OBS was separately constructed based on nutrients/lifestyle (NLOBS) and food groups/lifestyle (FLOBS) according to the previously proposed methods. PPD was diagnosed 4 to 6 weeks after delivery using the Edinburgh Postpartum Depression Scale. Cox proportional hazards regression was utilized to examine the relationship between OBS and PPD. Participants had a mean (SD) age of 30.9 ± 6.12 years. In total, 43 females were diagnosed with PPD. Findings revealed that, after controlling all confounders, subjects with the highest level of NLOBS, compared to the lowest, had a 69% lower risk of PPD (HR: 0.31
95% CI: 0.12-0.83). Although a significant inverse relation was found between FLOBS and PPD in the crude model (HR: 0.43
95% CI: 0.19-0.96)
this association was not significant in fully adjusted model (HR: 0.53
95% CI: 0.22-1.27). Considering subtypes of each score, inverse relations were significant for NOBS and LOBS, but not for FOBS. This study suggests that a higher OBS, particularly nutrient-based OBS, during pregnancy may be associated with a reduced risk of PPD. Further research is necessary to validate these findings.