Comparing standard and technology-assisted peer-delivered CBT for perinatal depression: A causal mediation study.

The ENHANCE non-inferiority trial that took place in a deprived setting in Pakistan demonstrated that a technology-assisted digital adaptation of the Technology Assisted Thinking Healthy Programme (THP-TAP) was no different than the face-to-face THP in improving symptoms of perinatal depression. The present study examines the mechanisms through which THP-TAP improved symptoms of perinatal depression (or not) compared to the face-to-face THP. We applied a counterfactual-based approach to mediation - particularly interventional effects - to decompose the total effect of the THP-TAP intervention on symptoms of perinatal depression into the following pre-specified indirect effects: number of sessions attended; behavioural activation; perceived social support; problem-solving and cognitive-restructuring skills; and peer empathy. Mediators were assessed at 3 months post-partum, and depressive symptoms were measured at 6 months using the Patient Health Questionnaire-9 (PHQ-9). Perceived social support in THP-TAP arm mediated an improvement in symptoms of perinatal depression compared to the standard face-to-face THP group (adjusted mean difference in PHQ-9 scores attributable to perceived social support in the technology-assisted digital adaptation of the THP group compared to the World Health Organisation THP group: -0.072, bias-corrected 95% confidence interval: -0.170, -0.018). There was no difference to support the indirect effects for all other mediators. Even in the absence of treatment superiority, our findings suggest that levels of perceived social support were an important feature of the THP-TAP intervention, which resulted in improved symptoms of perinatal depression. From a practical perspective, these findings highlight the importance of social connectedness as a mechanism of change, demonstrating that peer-delivered digital psychosocial interventions can successfully cultivate this relational component.