USA 1989.

Study characteristics
Methods	A double‐blind, randomised, 2‐arm placebo‐controlled trial. Women in the groups were of low weight, normal weight and high weight
Participants	The pregnant adolescent women who were at risk for zinc deficiency and enrolled in the prenatal clinic of Charity Hospital 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 a nurse, and data of their characteristics and background information were collected. At 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	Zinc (30 mg): (n = 268). Placebo: (n = 288) Women were randomly assigned to receiving tablets of 30 mg Zn as gluconate (the Z group) or as 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 by a tablet count at each clinic visit and questioning after delivery when details of labour and delivery events were collected.
Outcomes	Maternal outcomes Weight gain Placental weight Caesearan section Labour length Arm circumference Triceps skinfold thickness Neonatal outcomes Gestational age at birth Birthweight Low birthweight (< 2500 g) Preterm birth Birth length Head circumference Chest circumference Respiratory assistance
Notes	Reported compliance was good ‐ 87% consumed 6 or 7 tablets per week Dates of study: not disclosed Funding sources: supported by a US Department of Agriculture, Sciences and Education Administration, Human Nutrition Extramural Research Grant to the Tulane University Medical Center; a cooperative agreement (7USC, 427, 250A, 1624, 2201) between the US Department of Agriculture Agricultural Research Service, Human Nutrition Research Center, Grand Forks, ND, and Tulane University Medical Center; Tulane Universityl and the General Nutrition Corporation, Fargo, ND, which provided the placebo and zinc supplement Declarations of interest: not disclosed
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "randomly assigned."
Allocation concealment (selection bias)	Unclear risk	Quote: "randomly assigned."
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "double‐blind"; "identical‐appearing tablets".
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "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