Abstract: The systematic review included 15 studies, of which 14 were randomised controlled trials (RCTs). The interventions took place in recognised slums or poor urban or periurban areas. The study locations were mainly Bangladesh, India, and Peru. The participants included 9261 infants and children and 3664 pregnant women. There were no dietary intervention studies. All the studies identified were nutrient supplementation and educational interventions. The interventions included zinc supplementation in pregnant women (three studies), micronutrient or macronutrient supplementation in children (eight studies), nutrition education for pregnant women (two studies), and nutrition systems strengthening targeting children (two studies) intervention. Six interventions were adapted to the urban context and seven targeted household, community, or 'service delivery' via systems strengthening. The primary review outcomes were available from seven studies for LFA/HFA, four for LBW, and nine for length. The studies had overall high risk of bias for 11 studies and only four RCTs had moderate risk of bias. Overall, the evidence was complex to report, with a wide range of outcome measures reported. Consequently, only eight study findings were reported in meta-analyses and seven in a narrative form. The certainty of evidence was very low to moderate overall. None of the studies reported differential impacts of interventions relevant to equity issues. Zinc supplementation of pregnant women on LBW or length (versus supplementation without zinc or placebo) (three RCTs) There was no evidence of an effect on LBW (MD –36.13 g, 95% CI –83.61 to 11.35), with moderate-certainty evidence, or no evidence of an effect or unclear effect on length with low- to moderate-certainty evidence. Micronutrient or macronutrient supplementation in children (versus no intervention or placebo) (eight RCTs) There was no evidence of an effect or unclear effect of nutrient supplementation of children on HFA for studies in the meta-analysis with low-certainty evidence (MD –0.02, 95% CI –0.06 to 0.02), and inconclusive effect on length for studies reported in a narrative form with very low- to moderate-certainty evidence. Nutrition education for pregnant women (versus standard care or no intervention) (two RCTs) There was a positive impact on LBW of education interventions in pregnant women, with low-certainty evidence (MD 478.44g, 95% CI 423.55 to 533.32). Nutrition systems strengthening interventions targeting children (compared with no intervention, standard care) (one RCT and one controlled before-and-after study) There were inconclusive results on HFA, with very low- to low-certainty evidence, and a positive influence on length at 18 months, with low-certainty evidence. All the nutritional interventions reviewed had the potential to decrease stunting, based on evidence from outside of slum contexts; however, there was no evidence of an effect of the interventions included in this review (very low- to moderate-certainty evidence). Challenges linked to urban slum programming (high mobility, lack of social services, and high loss of follow-up) should be taken into account when nutrition-specific interventions are proposed to address LBW and stunting in such environments. More evidence is needed of the effects of multi-sectorial interventions, combining nutrition-specific and sensitive methods and programmes, as well as the effects of 'up-stream' practices and policies of governmental, non-governmental organisations, and the business sector on nutrition-related outcomes such as stunting.

Plain-language summary: Nutritional methods (interventions) to improve infant and young children's growth have not been comprehensively or systematically assessed for urban slums. We included 15 studies in the review, involving 9261 children less than five years old and 3664 pregnant women. About 73% of children were less than one year old. The interventions provided maternal education; nutrient supplementation of mothers, infants, and children; improving nutrition systems; or a combination of these but not dietary modification. The reliability of the studies was very low to moderate overall because studies were not designed to cope with research problems linked to urban slum communities, such as high mobility and high loss of participants to follow-up. This meant that the effectiveness of the intervention could not be properly assessed at later dates. We assessed the effect of interventions taking both statistical and clinical significance into account. Where intervention outcomes were statistically insignificant, we conclude there was 'unclear effect'. There was no effect of giving mothers nutrient supplementation on birth weight and length, there were inconclusive results for nutrient supplementation in infants and children on improving children's height or stunting status, there was a positive impact on birth weight of maternal education interventions where there was a positive difference in birth weight of 478 g in infants exposed to the intervention, and inconclusive results of improving health systems that support nutrition on children's stunting status and a positive effect on height. There were no reported side effects from these interventions. The review showed the need to better understand urban slum environments and their people as evidence showed that interventions included in this review were successful in other locations outside of urban poor areas. More evidence is needed of the effects of multi-sectorial interventions, combining nutrition-specific and sensitive methods and programmes, as well as the effects of 'up-stream' practices and policies of governmental, non-governmental organisations (NGOs), and the business sector to improve low birth weight and stunting in poor urban environments.