USA 1995.

Study characteristics
Methods	A double‐blind, randomised, placebo‐controlled trial
Participants	5058 medically indigent African‐American women receiving prenatal care in 4 Jefferson County (Alabama) Health Department clinics considered for selection The pregnant women who were both nulliparous and multiparous ranged between 13 and 44 years of age were included for the selection criteria. Of these women, 589 at 14 ‐ 23 weeks' gestation were selected for the randomisation trial based on a plasma zinc level below the estimated median for gestational age for the population at the time of enrolment in prenatal care Only 580 women's data completed for analysis due to 9 women had insufficient outcome data
Interventions	Zinc: 25 mg elemental zinc per day (n = 286) Placebo (n = 294) Women were randomly assigned to both the zinc supplement and placebo groups. Both group received a daily prenatal multivitamin/mineral tablet not containing zinc but containing folic acid, iron, and other minerals. The tablets were produced by Mission Pharmacal, San Antonio, Texas. Zinc supplement and placebo were prepared in a capsules by Rempak, Carteret, New Jersy, and only the zinc supplement contained 25 mg of zinc (zinc sulphate). Women were asked to take 1 of each supplement daily, but the time was not specified The zinc content of the tablets was verified independently in our laboratory. Prior to this study, pregnant women in this care system received only folic acid and iron supplementation For each woman, compliance was defined as the percentage of zinc tablets consumed compared with the number of days enrolled in the project prior to delivery During the study, women in both the zinc supplement and placebo groups were provided with a daily prenatal multivitamin/mineral tablet not containing zinc but folic acid, iron and other minerals
Outcomes	Maternal outcomes Pregnancy hypertension Neonatal outcomes Preterm birth Low birthweight Small‐for‐gestational age Stillbirth Neonatal death Neonatal sepsis Crown‐heel length Child mental and psychomotor development at 5 years
Notes	Adherence: mean was 78% of days for both groups. Adherence was defined as the percentage of zinc tablets consumed compared with the number of days enrolled in the project prior to birth Dates of study: March 1991 ‐ August 1993 Funding sources: supported by grants HD27289 and HD28119 from the National Institutes of Health, Bethesda, Md and by research contract DHHS 282‐92‐0055 from the Agency for Health Care Policy and Research, Rockville, Md Declarations of interest: not disclosed
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Computer‐generated random numbers.
Allocation concealment (selection bias)	Unclear risk	Method of allocation concealment not described
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "both caregivers and subjects were blind regarding the content of the supplement."
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Not reported but likely to have been done due to the use of a placebo
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Losses to follow‐up: samples unavailable from 24.7% (143/580 women; 63/294 (21.4%) in the zinc group and 80/286 (28%) in the placebo group At 5 years of age, results were available for 355/580 children (61%)
Selective reporting (reporting bias)	Unclear risk	Not enough information to make this judgement. No information on if the protocol had been published prior to the trial
Other bias	Low risk	No apparent source of other bias

BMI: body mass index; dL: decilitre; g: gram; GI: gastrointestinal; IU: international units; kJ: kilojoule; L: litre; LMP: last menstrual period; mg: milligram; PROM: premature rupture of membranes; RCT: randomised controlled trial; RDA: recommended daily allowance; RR: risk ratio; SD: standard deviation; µg: micrograms; µmol: micromoles