Table 1.

Summary of Meta-Analysis Estimates, Sorted by Outcome

Overall Consistency					Summary of Findings
Number of trials	Heterogeneity (quantitative)	Direction and statistical significance of results	Generalizability to resource poor settings	Heterogeneity of the intervention	Number of births	Statistical method	Pooled estimate (95% CI)
Risk of preterm birth (<37 weeks): Overall quality of evidence grade= low
16	Q = 20.3, p = 0.16; I2 = 26%	10 trials favored zinc; 2 of these statistically significant	11 trials conducted in low or middle income countries	Daily zinc dose from 15 to 50 mg; augmentative and placebo-controlled trials	7818 (963 preterm)	Mantel-Haenszel fixed-effects relative risk; Shore corrected 95% CI	0.86 (0.75, 0.99)
Risk of low birth weight (<2500 grams): Overall quality of evidence grade= very low
11	Q = 16.0, p = 0.10; I2 = 37%	4 trials favored zinc; 2 of these statistically significant	8 trials conducted in low or middle income countries	Daily zinc dose from 15 to 50 mg; augmentative and placebo-controlled trials	5614 (937 low birth weight)	Mantel-Haenszel fixed-effects relative risk; Shore corrected 95% CI	1.06 (0.91, 1.23)
Risk of small for gestational age birth (as defined by individual authors): Overall quality of evidence grade= very low
5	Q = 9.8, p = 0.04; I2 = 59%	2 trials favored zinc; 1 of these statistically significant	4 trials conducted in low or middle income countries	Daily zinc dose from 25 to 45 mg; augmentative and placebo-controlled trials	3441 (1155 SGA)	Mantel-Haenszel fixed-effects relative risk; Shore corrected 95% CI	1.03 (0.91, 1.17)
Mean difference in birth weight (grams): Overall quality of evidence grade= very low
20	Q = 77.4, p < 0.005; I2 = 75%	11 trials favored zinc; 2 of these statistically significant	13 trials conducted in low or middle income countries	Daily zinc dose from 5 to >50 mg; augmentative and placebo-controlled trials	8138	Inverse-variance weighted fixed-effects mean difference	13 g (−9, 35)
Mean difference in length at birth (centimeters): Overall quality of evidence grade= very low
12	Q = 16.0, p = 0.14; I2 = 31%	6 trials favored zinc; 1 of these statistically significant	9 trials conducted in low or middle income countries	Daily zinc dose from 5 to 50 mg; augmentative and placebo-controlled trials	6285	Inverse-variance weighted fixed-effects mean difference	−0.1 cm (−0.3, 0.0)
Mean difference in gestational age at birth (weeks): Overall quality of evidence grade= very low
12	Q = 12.0, p = 0.37; I2 = 8%	7 trials favored zinc; 1 of these statistically significant	11 trials conducted in low or middle income countries	Daily zinc dose from 5 to >50 mg; augmentative and placebo-controlled trials	5273	Inverse-variance weighted fixed-effects mean difference	0.1 cm (−0.1, 0.2)
Mean difference in head circumference at birth (centimeters): Overall quality of evidence grade= very low
11	Q = 21.0, p = 0.02; I2 = 52%	4 trials favored zinc; 2 of these statistically significant	9 trials conducted in low or middle income countries	Daily zinc dose from 5 to 50 mg; augmentative and placebo-controlled trials	5065	Inverse-variance weighted fixed-effects mean difference	0.0 cm (−0.1, 0.1)

Table format adapted from Walker, Fischer-Walker, Bryce et al., International Journal of Epidemiology, 2010;39:i21–i31 and Cochrane Review Manager “Data and Analysis” pre-formatted table.

95% CI = Ninety-five percent confidence interval

mg = milligrams

g = grams

cm = centimeters

SGA = Small for gestational age

Q = Cochrane’s heterogeneity statistic

I² = 100% × (Q − degrees of freedom)/Q

Quantitative measures of heterogeneity: large Q, small p, large I² all indicate increased heterogeneity

All included results were derived from randomized controlled trials.

For binary outcomes, sRR < 1 favors zinc intervention (unfavorable outcome less likely).

For continuous outcomes, sMD > 0 favors zinc intervention (larger, more developed infants).

Number of births and number of events were estimated for one trial.

All summary estimates were calculated by fixed effects meta-analysis. Random effects estimates are provided in the text when appropriate.