Data sources and search strategies

After formulating the research question and review objectives, a literature search was conducted to identify relevant studies in MEDLINE Ovid, EMBASE (Excerpta Medica database) Ovid and CINAHL EBSCO (Cumulative Index to Nursing & Allied Health Elton B. Stephens Co.), and PubMed from January 1, 2009, to March 17, 2021. A search strategy was created with the assistance of an experienced librarian for MEDLINE using text keywords and the following Medical Subject Headings (MeSH) terms with Boolean operators in order to maximize the combinations of terms scoped: “Child Development,” “Pediatric obesity,” “overweight,” “body mass index,” “breastfeeding,” and “gestational weight gain”. The search was modified for the additional electronic databases; Table S1 outlines the search syntax and strategy.

Inclusion criteria and study selection

Titles and abstracts identified from the search strategy were screened for relevancy by two authors and full-text articles reviewed for eligibility based on the inclusion criteria. Covidence, a systematic review software, was used to allow collaboration among reviewers. Review articles were not included but the reference lists of identified relevant reviews were scanned and relevant research studies identified were screened. At both stages of screening consistency of inclusion and exclusion were evaluated. Interrater agreement was tested with a subset of articles using Cohen’s kappa until substantial agreement was reached. ^{Reference Landis and Koch15} Records were screened independently and in the event of an unsolvable discrepancy a third team member was consulted. Eligible studies were included if the following criteria were met: (1) longitudinal research studies that pertained to singleton pregnancies; (2) maternal BMI (exposure) and child BMI between the age of two and eighteen (outcome) were reported according to WHO ^16–18 or Centers for Disease Control and Prevention (CDC) ^19,20 classifications; (3) peer-reviewed; (4) in the English language; and (5) contained a subgroup of children who were breastfed. Studies were excluded from full text-review if (1) the exposure variables of interest (maternal BMI and breastfeeding) were not independent variables and (2) the full text was not available. Since quality assessment of the included studies was beyond the objectives of a scoping review, ^{Reference Arksey and O’Malley12,Reference Levac, Colquhoun and O’Brien21} we forewent this aspect of analysis.

Data extraction

Data extraction was completed using customized Covidence data extraction forms to chart variables and summary statistics. Key data extraction variables were informed by the Joanna Briggs Institute (JBI) manual ²² and the Arksey and O’Malley framework. ^{Reference Arksey and O’Malley12} The analysis structure and organizational hierarchy was created to characterize major themes identified from the review according to Bronfenbrenner’s theory of ecological systems in which human development unfolds. ^{Reference Bronfenbrenner23,Reference Brofenbrenner24} Findings were further reported through a life course approach ^{Reference Heikkinen25} beginning with preconception variables.

Healthy behaviours lifestyle and social economic status

Eight studies examined the relationship between maternal smoking and child obesity of which five found significant results (Table S2). ^{Reference Demment, Haas and Olson29,Reference Bell, Yew, Devenish, Ha, Do and Scott34–Reference Ortega-García, Kloosterman and Alvarez37} Children whose mother smoked were significantly more likely to develop obesity than those not exposed to maternal smoking. Three studies attributed this relationship to fetal programming. ^{Reference Bell, Yew, Devenish, Ha, Do and Scott34,Reference Iguacel, Escartín and Fernández-Alvira36,Reference Ortega-García, Kloosterman and Alvarez37} One study found the relationship between maternal smoking and child growth trajectory was mediated by birth weight. ^{Reference Demment, Haas and Olson29} Three studies reported family eating practices influenced child eating patterns and food preferences. ^{Reference Weden, Brownell and Rendall33,Reference Ardic, Usta, Omar, Yildiz and Memis41,Reference Fairley, Santorelli and Lawlor42} In a US study of 4815 children, Black children were significantly less likely to have daily family dinners together and more likely to have a higher BMI when compared to White children. ^{Reference Weden, Brownell and Rendall33} In a UK study, indulgent caregiver feeding style was related to a significantly higher child BMI z-score. ^{Reference Fairley, Santorelli and Lawlor42} Three studies highlighted the influence of parental and child sedentary behaviors (e.g., TV viewing time, physical inactivity) on child growth trajectories. ^{Reference Demment, Haas and Olson29,Reference Bell, Yew, Devenish, Ha, Do and Scott34,Reference Al-Qaoud and Prakash39}

Children who were from families that reported a low social economic status (SES) and identified as belonging to a Black, Indigenous and People of Colour (BIPOC) groups are significantly more likely to have poor health behaviours (e.g., maternal smoking, excess parental weight, and sedentary lifestyles). ^{Reference Weden, Brownell and Rendall33} In an Australian study of 2186 families, a significant negative relationship was found between low SES, maternal smoking, maternal overweight/obesity, paternal overweight/obesity, shorter breastfeeding duration, and early introduction to solid foods, all which have been implicated in the development of childhood obesity. ^{Reference Iguacel, Chung, Gearon, Moreno, Peeters and Backholer35} Six studies found that children whose mothers had lower education achievement, were of low SES, and lived in low-income housing were significantly more likely to have a higher BMI and be classified overweight or obese; these children were also more likely to be of Hispanic or Black ethnicity. ^{Reference Demment, Haas and Olson29,Reference Wang, Martinez, Chow and Xiang32–Reference Bell, Yew, Devenish, Ha, Do and Scott34,Reference Ortega-García, Kloosterman and Alvarez37,Reference Sirkka, Vrijkotte and Halberstadt40}

Parental preconception anthropometrics and perinatal weight status

Regardless of SES or ethnicity, all 14 studies found maternal preconception and perinatal BMI consistently predicted childhood obesity. Women who were overweight were twice as likely to have a child who was also overweight or obese compared to children from normal weight women; this risk increased even further when the mother was obese supporting a genetic and fetal programming interrelationship. Three studies examined the influence of paternal BMI and found that paternal overweight or obesity status also increased the risk for child obesity when compared to normal weight fathers. ^{Reference Ventura, Loken and Birch30,Reference Iguacel, Chung, Gearon, Moreno, Peeters and Backholer35,Reference Iguacel, Escartín and Fernández-Alvira36} Further, there is growing evidence that maternal excess gestational weight gain (EGWG), as defined by WHO/IOM, ⁴⁴ influences child growth trajectories. Two cohort studies conducted in the US and Chile reported EGWG was significantly more likely among women who were overweight and obese ^{Reference Bider-Canfield, Martinez and Wang31,Reference Wang, Martinez, Chow and Xiang32,Reference Rios-Castillo, Cerezo, Corvalán, Martínez and Kain38} and in a US study, children whose mothers experienced EGWG were twice as likely to be overweight BMI trajectory between the ages of 2 and 15. ^{Reference Demment, Haas and Olson29}

Genetics, epigenetics and fetal programming

Environmental factors can result in intergenerational epigenetic changes to the developing fetus which can alter metabolic trajectories over the lifespan. Four studies examined the effect of parental ethnicity and found children who were Hispanic and Spanish Roma compared to other ethnicities; ^{Reference Iguacel, Escartín and Fernández-Alvira36} Turkish compared to Dutch; ^{Reference Sirkka, Vrijkotte and Halberstadt40} Black compared to White; ^{Reference Weden, Brownell and Rendall33} and White compared to Pakistani ^{Reference Fairley, Santorelli and Lawlor42} were more likely to have high BMI z-scores or be overweight and obese, respectively. It was hypothesized that overweight and obesity risk was enhanced in these ethnicities due to the exposure to a great number of risk factors such as lower SES, shorter breastfeeding durations, high parental BMI, and maternal smoking. ^{Reference Iguacel, Escartín and Fernández-Alvira36,Reference Fairley, Santorelli and Lawlor42} While none of the review studies included genetic data, the social trends found suggest epigenetic changes among these ethnicities may be attributable to weight gain through family health behaviors that promote obesogenic environments.

Early infant feeding

Recent studies suggest early infant feeding practices such as breastmilk intake and solid food introduction have lasting effects on child weight status in later life. Two studies reported breastfeeding duration was significantly shorter among women with obesity when compared to those who were normal weight. ^{Reference Bider-Canfield, Martinez and Wang31,Reference Iguacel, Chung, Gearon, Moreno, Peeters and Backholer35} Four studies found a shorter duration of breastfeeding, predominantly defined as less than 6 months postpartum, significantly increased a child’s obesity risk. ^{Reference Gannon, Pollock, Allen and Kling28,Reference Ventura, Loken and Birch30–Reference Wang, Martinez, Chow and Xiang32,Reference Rios-Castillo, Cerezo, Corvalán, Martínez and Kain38} Four studies found that when breastfeeding was not exclusive there was no significant protection and the risk of being overweight/obese remained. ^{Reference Demment, Haas and Olson29,Reference Iguacel, Escartín and Fernández-Alvira36,Reference Al-Qaoud and Prakash39,Reference Fairley, Santorelli and Lawlor42} The importance of breastfeeding exclusivity to the recommended 6 months was demonstrated in four studies. ^{Reference Bell, Yew, Devenish, Ha, Do and Scott34,Reference Ortega-García, Kloosterman and Alvarez37,Reference Sirkka, Vrijkotte and Halberstadt40,Reference Ardic, Usta, Omar, Yildiz and Memis41} These studies observed that when children were exclusively breastfed for ≥6 months they were less likely to become overweight or obese. A dose–response relationship was reported between breastfeeding and risk of child overweight/obesity. ^{Reference Weden, Brownell and Rendall33,Reference Bell, Yew, Devenish, Ha, Do and Scott34,Reference Ortega-García, Kloosterman and Alvarez37} Six studies examined the effect of complementary feeding of which four studies found a significant result. ^{Reference Bell, Yew, Devenish, Ha, Do and Scott34,Reference Al-Qaoud and Prakash39–Reference Ardic, Usta, Omar, Yildiz and Memis41} Solid food introduction before 5–6 months was also found to be an obese risk factor, ^{Reference Bell, Yew, Devenish, Ha, Do and Scott34,Reference Al-Qaoud and Prakash39,Reference Sirkka, Vrijkotte and Halberstadt40} while the delay of formula introduction was seen to reduce the risk of overweight and obesity. ^{Reference Ortega-García, Kloosterman and Alvarez37}

Infant growth trajectories

Five studies examine the effects of birthweight on child obesity of which four found a significant relationship. ^{Reference Gannon, Pollock, Allen and Kling28,Reference Bell, Yew, Devenish, Ha, Do and Scott34,Reference Rios-Castillo, Cerezo, Corvalán, Martínez and Kain38,Reference Al-Qaoud and Prakash39} Three studies reported rapid infant weight gain to be associated with adverse weight status and metabolic outcomes. ^{Reference Demment, Haas and Olson29,Reference Ventura, Loken and Birch30,Reference Iguacel, Escartín and Fernández-Alvira36} Children who had a rapid weight gain, determined by age specific weight z-scores from birth to 6 months, were almost four times more likely to be obese at 6 years of age in comparison to those who did not have an early rapid weight gain. ^{Reference Iguacel, Escartín and Fernández-Alvira36} Similar results were seen at 15 years of age, when weight-for-length from birth to 2 years was rapid ^{Reference Demment, Haas and Olson29} and when rapid weight gain occurred between the ages of 5 and 9 years. ^{Reference Ventura, Loken and Birch30} One study observed that when rapid infant weight gain occurred in females their high BMI trajectories were accompanied by increased fat mass and adverse total cholesterol, low-density lipoprotein cholesterol, insulin resistance, fasting insulin, triglyceride levels, and blood pressure. ^{Reference Ventura, Loken and Birch30}

Targeted prevention and intervention

Ten studies highlighted the need for early targeted intervention of modifiable risk factors among preconception women as well as those during pregnancy. ^{Reference Gannon, Pollock, Allen and Kling28,Reference Demment, Haas and Olson29,Reference Bider-Canfield, Martinez and Wang31,Reference Weden, Brownell and Rendall33–Reference Iguacel, Escartín and Fernández-Alvira36,Reference Sirkka, Vrijkotte and Halberstadt40,Reference Fairley, Santorelli and Lawlor42} A Netherland study found infant feeding and child BMI differ according to risk groups, encouraging the need for group-specific interventions. ^{Reference Sirkka, Vrijkotte and Halberstadt40} An Australian study suggested that interventions that promote healthy lifestyles and behaviors may aid in reducing socioeconomic inequalities in excessive child weight gain. ^{Reference Iguacel, Chung, Gearon, Moreno, Peeters and Backholer35} To limit the accumulative load of early life risk factors, one study suggested to preemptively intervene by summing the early life risk factors and use their cumulative risk as predictive tool. ^{Reference Gannon, Pollock, Allen and Kling28} Some of the included studies describe two risk factors that are important to public health strategies, (1) the promotion of sustained EBF ^{Reference Weden, Brownell and Rendall33,Reference Bell, Yew, Devenish, Ha, Do and Scott34} and (2) supporting healthy weight gain among parents ^{Reference Bider-Canfield, Martinez and Wang31,Reference Weden, Brownell and Rendall33,Reference Iguacel, Escartín and Fernández-Alvira36} to prevent childhood obesity. The collective call for early intervention effectively summarizes the community and policy influences on childhood obesity and how they are essential in helping prevent childhood obesity.

Limitations

Despite numerous strengths of this review, including a systematic approach and the inclusion of studies that use statistical logistic regression analysis to estimate the strength of the relationship between risk factors and child obesity, our review also has a few limitations. Due to the nature of the scoping review, our study did not assess the quality of the studies that were analyzed. Our review also only included longitudinal observational cohorts; inherently, this study design is limiting as causal inferences cannot be made. An RCT study design would be more effective in providing the highest quality of evidence and minimizing bias. Future reviews would be strengthened by including RCT study designs as an inclusion criterion. It is likely that our results regarding breastfeeding protection were discordant due to the fact the many modes of breastfeeding may vary according to sociocultural practice ^{Reference Scott and Binns69} and for this reason, the definition of exclusive, nonexclusive, full- or any breastfeeding can differ based on culture and region. The universal adoption of the definition of exclusive and nonexclusive breastfeeding would allow for better comparison and analysis between studies. Finally, we acknowledge our synthesis was based on outcomes reported as BMI measurements of growth or weight status, because we did not consider other measurements of weight or fat mass the generalization of our results may be limited.