App usability, engagement, and postpartum weight retention: secondary analysis of the INTER-ACT randomized controlled trial

Abstract

Objective: To examine whether perceived usability of the INTER-ACT app influences postpartum weight loss and whether this effect is mediated by app use, motivational power, and implementation of lifestyle recommendations. Patients and Methods: Dutch-speaking women aged 18 years or older who had delivered a singleton infant and exceeded the recommended guidelines of the Institute of Medicine (IOM) for gestational weight gain got recruited between May 2017 and April 2019, Across six Flemish hospitals. This secondary analysis included 138 participants of the INTER-ACT intervention arm. At 6 months postpartum participants completed a process evaluation survey, assessing app usability using 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 were conducted, adjusting for maternal age, parity, and pre-pregnancy BMI. Results: App usability was moderate (mean SUS=60.6) and positively associated with perceived app use frequency (B=.05, p<.001), motivational power (B=.003, p<.001), and implementation of lifestyle recommendations (B=.01, p=.036), but not with weight loss. Usability showed no total, direct, or indirect effect on weight loss. Gestational weight gain (GWG) was the only significant predictor (B=0.24, p=0.003). Higher usability was also associated with more positive and fewer negative emotional responses (p<.05). Conclusion: App usability was associated with engagement and positive emotional experience, but not with reduced PPWR. GWG remained the main determinant of postpartum weight outcomes. Preventing EGWG and complementing this with emotionally supportive postpartum mHealth tools may improve outcomes. Trial registration: ClinicalTrials.gov;NCT02989142.