Adverse lifestyle factors in the periconception and early life period, including high maternal prepregnancy BMI and excessive gestational weight gain, are important risk factors for childhood obesity. Early prevention is key, but results from systematic reviews of preconception and pregnancy lifestyle interventions have shown mixed success in improving children's weight outcomes and adiposity. We aimed to investigate the complexity of these early interventions and process evaluation components and authors' statements to improve our understanding regarding their limited success.