Why do preconception and pregnancy lifestyle interventions demonstrate limited success in preventing overweight and obesity in children? A scoping review investigating intervention complexity, process evaluation components, and author interpretations.

Preventing childhood obesity from early life is considered essential. However, evidence from recent systematic reviews has highlighted inconsistent results and limited effectiveness of preconception and pregnancy lifestyle interventions regarding offspring weight outcomes and adiposity. Therefore, to improve our understanding regarding the mixed success of these early life interventions, we conducted a scoping review examining intervention complexity, process evaluation components, and authors' statements. Eligible articles (preconception or pregnancy lifestyle trials with offspring data beyond 1 month of age) were identified by searching databases (PubMed, Embase, and CENTRAL), previous reviews, and performing CLUSTER searches. The Intervention Complexity Assessment Tool for Systematic Reviews (iCAT_SR) was used to evaluate intervention complexity. A thematic analysis provided insight into process evaluation components and authors' interpretations. Finally, an expert consultation on the results was conducted. We identified 40 eligible publications corresponding to 27 trials. Only two trials started before conception. Potential reasons for interventions' limited success included the late intervention initiation, short intervention duration, and insufficient sample size. Few studies reported process evaluations and included stakeholder involvement, which are essential according to the expert group. We discuss current limitations and outline suggestions for future interventions in this field of research.