Application Usability, Engagement, and Postpartum Weight Retention: Secondary Analysis of the INTER-ACT Randomized Controlled Trial

Abstract Background Postpartum weight retention (PPWR) is a key contributor to long-term obesity risk and an important determinant of maternal health. Mobile health (mHealth) interventions may support postpartum change to a healthier lifestyle, but their effectiveness may depends on usability. This study examined whether perceived usability of the INTER-ACT app was associated with weight loss at 6 months postpartum and whether this association was mediated by app use frequency, motivational power, and implementation of lifestyle recommendations. Methods This secondary analysis used data from the intervention arm of the INTER-ACT randomized controlled trial (RCT), which provided postpartum lifestyle coaching and a supportive app to women with excessive gestational weight gain (EGWG). Participants (n=138) completed the process evaluation survey at 6 months postpartum, which included the System Usability Scale (SUS), perceived motivational power, and perceived implementation of lifestyle recommendations. Weight loss was calculated between 6 weeks and 6 months postpartum. Pearson correlations and parallel mediation analyses tested associations between usability, engagement-related variables, and weight loss, adjusting for maternal age, parity, and pre-pregnancy BMI. Results The INTER-ACT app demonstrated moderate usability (mean SUS=60.6). Usability was positively associated with app use frequency (B=.05, p