Examining psychological inflexibility as a mediator of postpartum depressive symptoms: A longitudinal observational study of perinatal depression

Background: Depression is a common, serious complication during the postpartum period. Predictors of postpartum depression characterize who is at-risk for persistent symptoms. This study explored how psychological inflexibility affects depressive symptoms at 4 and 12 weeks postpartum. Methods: Participants receiving prenatal care at a medical center were recruited during the second trimester. Participants (n = 180) completed online assessments and diagnostic interviews during the third trimester (>= 28 weeks gestation), and at 4-, 8-, and 12-weeks postpartum. Online assessments measured psychological inflexibility (PI) and depressive symptoms, while diagnostic interviews measured lifetime history of depression. Results: Mediation analysis examined pathways between 4-weeks postpartum depression, 8-weeks postpartum PI, and 12-weeks postpartum depression. Depressive symptoms at 4-weeks postpartum predicted PI at 8-weeks postpartum (0 = 0.31, SE = 0.06, t (177) = 6.06, p < .001). Depressive symptoms at 4-weeks postpartum (0 = 0.42, SE = 0.06, t (176) = 7.12, p < .001) and PI at 8-weeks postpartum (0 = 0.32, SE = 0.08, t (176) = 4.09, p < .001) predicted depressive symptoms at 12-weeks postpartum. Depressive symptoms at 4-weeks, 8-week PI, and lifetime history of depression accounted for 42% of the variance in 12-week depressive symptoms (R2 = 0.42). The confidence interval of the indirect effect (0.04, 0.18) did not include zero, indicating significant mediation by PI. Conclusions: PI mediated the relation between 4- and 12-weeks postpartum depressive symptoms when controlling for lifetime history of depression. Psychological inflexibility is a transdiagnostic target for future prevention and intervention research during the postpartum period.