Summary of findings for the main comparison. Zinc supplementation in pregnant women versus supplementation without zinc or placebo to reduce stunting in children (low birth weight, length at birth and at 12 months).

Zinc supplementation in pregnant women versus supplementation without zinc or placebo to reduce stunting in children (low birth weight, length at birth and at 12 months)
Patient or population: pregnant women Settings: poor urban slums Intervention: zinc supplementation Comparison: supplementation without zinc or placebo
Outcomes	Relative effect (95% CI)	No of participants (studies)	Certainty of the evidence (GRADE)	Comments
Length (cm) at birth	No evidence of an effect: MD –0.13 (–0.36 to 0.10)	1337 (2)	⊕⊕⊕⊝ Moderatea	Caulfield 1999; Osendarp 2000
Length (cm) at 12 months	Unclear effect: 0.13, SD 0.16 (longitudinal regression modelling, adjusted for age; age quadratic; age–treatment interaction; sex; sex–treatment interaction; birth anthropometric measure; maternal anthropometry; primiparity; breastfeeding; complementary feeding in previous months; diarrhoea morbidity; and hygiene and sanitation index)	237 (1)	⊕⊕⊝⊝ Lowb	Iannotti 2008
Low birth weight (g)	No evidence of an effect: MD –36.13 (–83.61 to 11.35)	1367 (2)	⊕⊕⊕⊝ Moderatec	Caulfield 1999; Osendarp 2000
CI: confidence interval; MD: mean difference; SD: standard deviation. GRADE Working Group grades of evidence High certainty: further research is very unlikely to change our confidence in the estimate of effect. Moderate certainty: further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate. Low certainty: further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate. Very low certainty: we are very uncertain about the estimate.

^aThe overall risk of bias was high for Iannotti 2014. We downgraded two levels for indirectness of evidence (geographical coverage) and precision. Refer to Appendix 14 for more details.
 ^bThe overall risk of bias was high for Caulfield 1999 and moderate for Osendarp 2000. We downgraded one level for indirectness of evidence (geographical coverage). Refer to Appendix 14 for more details.
 ^cThe overall risk of bias was high for Caulfield 1999 and moderate for Osendarp 2000. We downgraded one level for indirectness of evidence (geographical coverage). Refer to Appendix 14 for more details.