Risk factors in the first 1000 days of life associated with childhood obesity: a systematic review and risk factor quality assessment.

Background Adverse early life exposures might negatively affect foetal and infant development, predisposing children to obesity. We aimed to systematically identify and evaluate risk factors for childhood obesity in preconception, pregnancy, and infancy, and assess their potential as targets for future prediction and prevention strategies. Methods This systematic review (PROSPERO, CRD42022355152) included longitudinal studies from selected electronic databases published between inception and August 17th, 2022, identifying maternal, paternal, or infant risk factors from preconception until infancy for childhood obesity between 2 and 18 years. Screening and data extraction was performed through standardized extraction forms. We assessed risk factor quality on modifiability and predictive power using a piloted criteria template from ILSI-Europe-Marker-Validation-Initiative. Findings We identified 172 observational and 5 intervention studies involving n=1.879.971 children from 37, predominantly high-income, countries. 59%, 25% and 16% of studies measured childhood obesity between 2- <6 years, 6-10 years, and >10 -18 years respectively. Average reported childhood obesity prevalence was 11.1%. Pregnancy and infancy risk factors were mostly studied. We identified 59 potential risk factors, 24 of which were consistently associated with childhood obesity risk. Higher maternal prepregnancy weight (n=28/31 positive associations from 31 studies, respectively), higher gestational weight gain (n=18/21), maternal smoking during pregnancy (n=23/29), higher birth weight (n=20/28), LGA (n=17/18), no breastfeeding (n=20/31), and higher infant weight gain (n=12/12) were the strongest risk factors, which may aid in prediction or be targets for prevention. Level of evidence was generally moderate due to unreliable exposure measurement, short follow-up/loss-to-follow up, and risk of confounding. Interpretation We identified 7 early life risk factors, which were strongly associated with a higher risk of childhood obesity, and can contribute to future prediction and prevention strategies. These findings support implementation of prevention strategies targeting these early-life risk factors from a clinical and population perspective, where possible integrated with implementation studies. Funding This work was conducted by an expert group of the European branch of the International Life Sciences Institute, ILSI Europe.