Denmark 1996.

Methods	A double‐blinded, randomised placebo‐controlled trial.
Participants	Normal healthy middle‐class women were (at least 18 years old) less than 20 weeks pregnant confirmed by scan for their first visit and booked for delivery at Kolding hospital and Horsens hospital, Denmark. Any known intolerance towards zinc, diabetes mellitus, thyrotoxicosis or earlier rhesus immunization were excluded from the trials. The women thought likely to be zinc deficient by the previous study project 'Pregnancy, environment and way of life' in Denmark.
Interventions	Women received 2 tablets of Zinclet@ (44 mg elemental zinc in total) or 2 placebo tablets containing inert substances. They were indistinguishable in appearance and taste. The tablets were prepared by the Gunnar Kjems Aps company. Women were advised to take 2 tablets daily after breakfast and to avoid taking tablets possibly containing iron together with those of the study, as iron reduces zinc uptake. Women were excluded later, if there were any side‐effects caused by the tablets, if they wanted to stop or if she had not taken the tablets for 14 days in all. Zinc: 2 tablets with 44 mg elemental zinc (n = 1000). No zinc: 2 placebo tablets indistinguishable from active tablets (n = 1000).
Outcomes	Maternal outcomes Prelabour rupture of membranes; preterm labour; pre‐eclampsia; antepartum haemorrhage; caesarean section. Neonatal outcomes Low 5‐minute Apgar score; large‐for‐gestational age; small‐for‐gestational age; birthweight (not able to be used in graphs since no SDs provided).
Notes	Adherence: non‐adherers were excluded from the final analysis; reasons included side‐effects from tablets, if a woman wished to stop or if a woman had not taken the tablets for 14 days in all. The authors noted that women did not differ in basic characteristics. There were however, significantly more smokers in the non‐adherers group and thus the numbers in the final analysis related to labour and birth have also excluded smokers.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Randomisation was performed in successive groups of 10 active and 10 placebos; no further details reported.
Allocation concealment (selection bias)	Unclear risk	Not reported.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Investigators and mothers were blinded.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Not reported, but probably done as paper reports that the code was not broken until the end of the study.
Incomplete outcome data (attrition bias) All outcomes	High risk	794/2000 (39.7%); 415 in zinc group and 379 in placebo group.
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	Unclear risk	Analyses relating to labour and birth excluded smokers.