UK 1991a.

Methods	A double‐blind, randomised, placebo‐controlled trial. It was a 2‐arm trial.
Participants	56 pregnant women between 15‐25 weeks of pregnancy were selected at St Thomas' Hospital, London, UK. To fulfil the criteria for eligibility, women with low maternal pre‐pregnancy weight (less than 95% ideal body weight) were selected. For this study, Asian women and primigravidae who smoked more than 5 cigarettes per day with previous small‐for‐gestational‐age baby were set as criteria. For the zinc supplement group, women with previous small‐for‐gestational‐age baby, Asian, with low pre‐pregnancy weight and primigravidae who smoked were included. The placebo group were women with low pre‐pregnancy weight, previous small‐for‐gestational‐age baby, Asian, primigravidae who smoked. Social class was allocated from the classification of the Office of Population Censuses and Surveys (1980); classes 4‐7 were grouped as lower socio‐economic.
Interventions	A coded placebo and non‐placebo tablet were prepared by Thames Laboratories Ltd, UK. The effervescent Zn table were 22.5 mg. Zinc: 22.5 mg elemental zinc (n = 30). Placebo: (n = 26).
Outcomes	Maternal outcomes Pregnancy hypertension; preterm delivery; post‐term labour; induction of labour; caesarean section; Neonatal outcomes Small‐for‐gestational age; low birthweight; birthweight > 3500 g; congenital malformations; stillbirth/neonatal death.
Notes	Adherence was 43% in the zinc group and 67% in the placebo group ‐ outcomes were presented separately for adherers and non‐adherers.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Random number table, no mention of how the numbers were generated but probably adequately done.
Allocation concealment (selection bias)	Unclear risk	"coded placebo or non‐placebo tablet or 22.5 mg effervescent zinc...was randomly prescribed."
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Described as double‐blind, "all clinical decisions were made by staff in the labour and delivery wards who were unaware of the trial details".
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Not reported, but probably done.
Incomplete outcome data (attrition bias) All outcomes	Low risk	4/60 (7%); 2 women moved home, 1 termination of pregnancy, 1 miscarriage (all in the placebo group).
Selective reporting (reporting bias)	Unclear risk	Trial did not report all of the primary outcomes expected or specified for this review.
Other bias	Low risk	No apparent source of other bias.