China 2001.

Methods	A double‐blind, randomised, placebo‐controlled trial. A 4‐arm trial.
Participants	146 pregnant women, less than 12 weeks' gestation, who were living in southwest Shanghai, Maqiao countryside and was attending the prenatal clinic at Maqiao Primary Health Care Center were selected for the study. The people living in this area were uneducated with nutritional knowledge, and took cereal‐based diet with a little even no milk or milk products; therefore, they were supposed to have mild to moderate zinc deficiency according to Chinese recommended dietary allowance. The zinc content of drinking water in this area was considered negligible and no women received folic acid, iron supplementation and any commercial nutrition products during this trial study.
Interventions	For the zinc treatment groups, zinc lactate in capsule were given daily. Group A (GpA, 5 mg/day of zinc (n = 27)); Group B (GpB 10 mg/day of zinc (n = 40)); Group C (GpC, 30 mg/day of zinc (n = 39)). Group D was given placebo where the capsule was of maize starch. (GpD, 0 mg/day of zinc (n = 40)). All capsules were prepared by Laboratory, Second Military Medical University with indistinguishable appearance. Women were instructed to take a single capsule per day 1 hour before or 3 hours after the evening meal. The content of the capsules and the code of the capsule bottles were not known by the investigator or the pregnant women. Only 156 women were followed up under antenatal care.
Outcomes	Maternal outcomes Caesarean section; weight gains; gestational age; intrauterine growth restriction; duration of labour; oxygen demand; forceps. Neonatal outcomes Small‐for‐gestational age; neonatal sepsis; low birthweight; congenital malformations; stillbirth; preterm birth. Apgar score; chest, neck, head circumference; crown‐heel length; ponderal index.
Notes	For the purposes of this review, Group A, B and C were combined as an intervention group and Group D served as a control group.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	No description other than the allocation was made randomly.
Allocation concealment (selection bias)	Low risk	All capsules were prepared by pharmacy and allocation was concealed for both investigators and women.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	All capsules were prepared by pharmacy and both investigators and enrolled pregnant women were concealed.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	No description.
Incomplete outcome data (attrition bias) All outcomes	Low risk	No drop outs for maternal and neonatal clinical outcomes reported.
Selective reporting (reporting bias)	Unclear risk	There is no information on protocol published prior to this trial and no information to make appropriate judgements on this.
Other bias	Unclear risk	It was reported that obstetric and physical background data between the groups were not significantly different, though actual data were not reported.