USA 1989.

Methods	A double‐blind, randomised, placebo‐controlled trial. It was a 2‐arm trial for women in the groups of low weight, normal weight and high weight.
Participants	The pregnant adolescent woman who were at risk for zinc deficiency and enrolled in the prenatal clinic of Charity Hospsital of New Orleans, a large urban state‐supported hospital serving area women without access to private maternity care, were considered for the trial. At the first clinic visit, the pregnant adolescent woman attended the a nutrition lecture presented by nurse and data of their characteristics and background information were collected. In the second visit, 652 low‐income pregnant adolescent women who were at less than 25 weeks' gestation (average age 17.6 years; range 13.5 to 19.6) were recruited for the trial. Women were grouped by their weight percentile, and treatment group. Total of 556 completed the study.
Interventions	Women were randomly assigned to receiving tablets of 30 mg Zn as gluconate the Z group or the placebo (P) group containing cellulose. A sample of blood was taken for chemical analysis and the previous 24‐hour dietary assessments were repeated 8‐10 weeks after enrolment. The course of the pregnancy was documented by the physician at each prenatal visit. Compliance with the treatment regimen was assessed bu a tablet count at each clinic visit and questioning after delivery when details of labour and delivery events were collected. Zinc (30 mg): (n = 268). Placebo: (n = 288).
Outcomes	Maternal outcomes Preterm birth; weight. Neonatal outcomes Birthweight; respiratory assistance.
Notes	Reported compliance was good ‐ 87% consumed 6 or 7 tablets per week.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	"randomly assigned."
Allocation concealment (selection bias)	Unclear risk	"randomly assigned."
Blinding of participants and personnel (performance bias) All outcomes	Low risk	"double‐blind"; "identical‐appearing tablets".
Blinding of outcome assessment (detection bias) All outcomes	Low risk	"Neither the subjects nor the investigators were informed of tablet identity until after completion of the data collection."
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Losses to follow‐up: 10.9% (71/652) at entry and 14.7% (96/652) [cumulative] at birth. Breakdown of losses by group was not reported, nor were reasons for losses.
Selective reporting (reporting bias)	Unclear risk	A number of primary maternal, pregnancy and neonatal outcomes were not reported (e.g. caesarean, postpartum haemorrhage, perinatal death).
Other bias	Low risk	No apparent source of other bias.