Table 1.

Characteristics of included papers

Authors, year, country, trial name, study design	No. of participants (% of original sample)	Study population, setting and intervention duration	Outcome definition and timing	Intervention content and delivery agent	Risk of biasa
Narrative syntdesis and ICA
Daniels et al., 2012, Australia, The NOURISH RCT, RCT26	N = 541 (77.5%)	First-time, generally affluent mothers with mean age of 30 years. Healthcare. 3 months	WAZ change and >0.67 change in WAZ (binary 1/0) between 0 and 14 months	Behaviourally focused intervention promoting healthy feeding strategies when introducing solids foods. Delivered by dietitians and psychologists	Low to moderate risk
Edmunds et al. 2014, The USA, WIC, Observational study30	N = 157.590 (−)	Low-income mothers with mean age of 26.6 years. Healthcare and community. 5 years	>0.67 change in WAZ (binary 1/0) between 0 and 12 months	Behaviourally focused and community-based intervention providing nutritious supplemental foods, breastfeeding support, nutrition education, and medical and social referrals. Delivered by health professionals	Moderate risk
Karanja et al. 2010, The USA, The TOTS Trial, Two-armed separate sample pretest–posttest study31	N = 177 (86.3%)	Mothers from a native population with a mean age of 25 years. Home and community. No information on duration	WAZ change between 0 and 24 months	Behaviourally focused and community-based intervention promoting breastfeeding and reducing sugar-sweetened beverages. Delivered by community workers	Moderate to high risk
Koletzko et al. 2009, Belgium, Germany, Italy, Poland, and Spain, The CHOP Study, RCT11	N = 635 (55.8%)	General population of mothers with a mean age of 30 years. Home. 12 months	WAZ change between 0 and 3, 6, 12 and 24 months	Non-behaviourally focused intervention providing low or high protein content formulas. Delivered by researchers	Low risk
Lakshman et al. 2018, The UK, The Baby Milk Trial, RCT27	N = 586 (87.6%)	General healthy formula feeding mothers. Home and healthcare. 6 months	WAZ and >0.67 change in WAZ (binary 1/0) between 0 and 6 and 12 months	Behaviourally focused intervention reducing formula-milk intake, promoting responsive feeding, and monitor growth. Delivered by health professionals	Low risk
Paul et al. 2011, The USA, The SLIMTIME Pilot Study, RCT28	N = 110 (68.8%)	First-time, generally affluent mothers with mean age of 27 years. Home. 6 months	CWG between 0 and 12 months	Behaviourally focused intervention promoting healthy practices in terms of (i) infant sleep and/or (ii) introduction to solid foods. Delivered by health professionals	Moderate to high risk
Savage et al. 2016, The USA, The INSIGHT Trial, RCT29	N = 250 (85.9%)	First-time, generally affluent mothers with mean age of 29 years. Home. 10 months	CWG between 0 and 6 months	Behaviourally focused intervention promoting responsive parenting focusing on infant emotional regulation, feeding, active social play, sleep and growth chart education. Delivered by health professionals	Low to moderate risk

Authors, year of publication, country	Relation to included trial	Study aim	Informants and data collection	Method of analysis	Weighting of study findingsa
Thematic synthesis and ICA
Guell et al. 2018, The UK33	The Baby Milk Trial	To explain some of the underlying mechanisms that might have been at play when implementing and participating in The Baby Milk Trial and shaped its outcome	10 intervention and 9 control mothers and 3 health professionals contributed in 22 individual interviews	Thematic analysis	High
Lakshman et al. 2012, The UK34	The Baby Milk Trial	To explore the views of healthcare professionals and bottle-feeding mothers on: (i) the Programme for Healthy Growth and Nutrition during infancy; (ii) the trial design for the planned Baby Milk trial and (iii) two draft leaflets	10 mothers contributed in 3 focus groups discussions and 8 health professionals and one mother contributed in 9 individual interviews	Hierarchical thematic framework	Moderate to high
Redsell et al. 2010, The UK39	No	To explore UK parents’ beliefs on infant’s size, growth and feeding behaviour and parental receptiveness to early intervention aimed at reducing the risk of childhood obesity	38 parents contributed in six focus groups	Thematic analysis	Moderate to high
Redsell et al. 2017, The UK38	No	To assess the feasibility and acceptability of using digital technology for Proactive Assessment of Obesity Risk during Infancy with the UK health visitors and parents	12 parents and 15 health professionals contributed in 27 individual interviews	Thematic content analysis	Moderate to high
Thébaud 2015, Australia36	The NOURISH RCT	To develop and apply an evaluation framework based on pre-existing effect and process data collected as part of the NOURISH RCT, an obesity prevention research programme starting early in infancy	344 mothers responded to questionnaires that included open-ended questions and health professionals ratings of 293 intervention sessions	Thematic content analysis	Low to moderate
Valencia et al. 2016, The USA37	Indirectly (WIC population)	To conduct a formative assessment among the WIC population in Southern Arizona, a group with a high percentage of Latino families, to evaluate mothers’ perceptions of infants’ growth/weight change in early life	34 mothers and 19 caregivers contributed in 7 focus groups and 6 individual interviews were conducted with health professionals	Grounded theory	Moderate
Authors, year of publication, country	Related to included trial	Study aim	Informants and data collection	Method of analysis	Weighting of study findings a
ICA only
Lakshman et al. 2014, The UK35	The Baby Milk Trial	To describe the experience of using the 2008 Medical Research Council’s framework to develop and evaluate a theory-based, behavioural infant feeding intervention aimed at preventing childhood obesity, including benefits and challenges of using this framework	Different health professionals and stakeholder-mothers were interviewed using both individual and focus group interviews to inform intervention development	Not specified in paper	Low

^aBased on quality appraisal.

WAZ, weight-for-age z-scores; WIC, The Special Supplemental Nutrition Program for Women, Infants and Children; CWG, conditional weight gain.