Chile 2001.

Methods	A double‐blind, randomised, placebo‐controlled trial.
Participants	804 pregnant adolescents were recruited from 5 Primary Care Centres in southern urban slums in Santiago, Chile. They were selected from their prenatal clinic visits before 20 weeks of gestation and aged < 19 years at the estimated time of delivery. The pregnant adolescents identified with chronic diseases, drug abuse, mental retardation, illiteracy or those with pregnancies due to incest or rape were not considered. Subgroup of 220 randomly selected pregnant adolescents at their 28‐30 weeks of gestation with a low zinc intake (7.4 SD 2.3 mg) at the initial admission were evaluated for dietary nutrient intake. Women showed adequate protein intakes but a relatively low mean energy intake.
Interventions	Zinc‐supplemented group (S) received 20 mg of Zn capsules daily (sulphate), or the placebo group (P) received an equivalent capsule of a placebo containing lactose. The group codes changed twice during the study and were kept by the pharmacist who prepared the capsules until the end of computational analysis for double‐blinding procedure. The individuals who ingested less than 50% of the capsules in any month of the study were excluded. All subjects received 40 mg iron (sulphate) supplements daily. Compliance with zinc intake was evaluated by counting the remaining capsules during the monthly visits. Zinc: 20 mg zinc/day (n = 249). Placebo: (n = 258). All women also received 40 mg iron per day.
Outcomes	Maternal outcomes Pre‐eclampsia; plasma zinc; hair zinc; gestational age at birth; preterm birth; maternal oedema; maternal cholestasis. red blood cell membrane alkaline phosphatases; plasma alkaline phosphatases . Neonatal outcomes Low birthweight; birthweight; spontaneous abortions; length at birth; head circumference.
Notes	Adherence: non‐adherers were excluded from analysis; this included individuals who ingested less than 50% of zinc supplements in any month of the study.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	"randomly assigned" ‐ no further details reported.
Allocation concealment (selection bias)	Unclear risk	"randomly assigned"; pharmacist kept codes ‐ no further details reported.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	"double‐blind fashion."
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not reported.
Incomplete outcome data (attrition bias) All outcomes	High risk	Losses to follow‐up: 297/804 (37%) ‐ failure to come to visits (137), taking less than 15 zinc capsules in any 1 month (115), spontaneous abortion (12), intervention began after 20 weeks' gestation (10), absence of pregnancy (7), change of address (6), apparent intolerance to zinc or placebo (6), twin pregnancy (4).
Selective reporting (reporting bias)	Unclear risk	Not all expected maternal primary outcomes reported, but most primary infant outcomes specified in this review were reported.
Other bias	Low risk	No apparent risk of other bias.