UK 1989.

Methods	A double‐blind, randomised, placebo‐controlled trial.
Participants	500 women who were less than 20 weeks pregnant at the first visit booking for delivery at Southmead Hospital, Bristol were recruited for study. An ultrasound scan was done in 95% of cases. At the end of the visit potential volunteers were seen by the research midwife, who explained the study fully. Median zinc concentrations at enrolment were 1.192 µmol/10 x 10 cells in the zinc group and 1.147 in the placebo group. 494 women remained to complete the study.
Interventions	Women were randomly allocated to receive a capsule containing 20 mg elemental zinc (66 mg zinc sulphate) oral capsule containing inert substances (sucrose, maize starch, purified talc, kaolin, gelatin) but which was indistinguishable in appearance and taste from the one containing zinc. The capsules were prepared by Smith Kline and French Ltd. The mothers were advised to take 1 capsule daily after breakfast. Serum haemoglobin and ferritin concentrations were measured in all women at the first visit. Iron and folate supplementation was advised only if the haemoglobin concentration was less than 100 g/l or the serum ferritin concentration was less than 10 µg/l. Supplementation capsule supply were provided enough to last until the next visit. The research midwives visited the women at the 28‐32 weeks and again on the day of delivery. During the study and after delivery clinical details were recorded by the research midwife by interview as well as from the case records. Compliance was assessed by the regularity with which the study capsules were taken. Those who took the supplement daily or on most days were grouped as compliers, and the rest were regarded as non‐compliers. Zinc: 20 mg elemental zinc (n = 246). No zinc: placebo (n = 248).
Outcomes	Maternal outcomes Preterm delivery (< 37 weeks); post‐term delivery (> 42 weeks); prelabour rupture of membranes; pregnancy hypertension; any maternal infection ‐ (pre or postdelivery); caesarean section; postpartum haemorrhage; congenital malformations; Neonatal outcomes Low birthweight (< 2500 g); birthweight > 3500 g; small‐for‐gestational age (< 10th centile); Apgar score at 1 minute < 6; Apgar score at 5 minutes < 8; stillbirth/neonatal death.
Notes	Adherence: adherence levels were not reported, but non‐adherers were included in study results. At 28 to 32 weeks' gestation, just over half the women claimed to be taking the supplement every day, and nearly two‐thirds were doing so by the time of giving birth. Although results were not presented separately for adherers and non‐adherers, the authors state that no significant differences between them were found, apart from a significantly lower risk of postpartum infection among the adherers.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Computer‐generated randomisation tables.
Allocation concealment (selection bias)	Low risk	Bottles prepared by drug company and labelled A/B.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Use of placebo; code not broken until the end of the study.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Not reported but likely to have been done due to use of placebo.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Losses to follow‐up: 6/500 (1%) ‐ 4 women moved and 2 miscarried.
Selective reporting (reporting bias)	Low risk	Most of the outcomes specified in the review were reported.
Other bias	Low risk	No apparent risk of other bias.