Zinc supplementation for improving pregnancy and infant outcome.
BACKGROUND
It has been suggested that low serum zinc levels may be associated with suboptimal outcomes of pregnancy such as prolonged labour, atonic postpartum haemorrhage, pregnancy-induced hypertension, preterm labour and post-term pregnancies, although many of these associations have not yet been established.


OBJECTIVE
To assess the effects of zinc supplementation in pregnancy on maternal, fetal, neonatal and infant outcomes.


METHODS
We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (30 September 2011) and reference lists of retrieved studies.


METHODS
Randomised trials of zinc supplementation in pregnancy. We excluded quasi-randomised controlled trials.


METHODS
Three review authors applied the study selection criteria, assessed trial quality and extracted data. When necessary, we contacted study authors for additional information.


RESULTS
We included 20 randomised controlled trials (RCTs) reported in 51 papers involving over 15,000 women and their babies. Trials were generally at low risk of bias. Zinc supplementation resulted in a small but significant reduction in preterm birth (risk ratio (RR) 0.86, 95% confidence interval (CI) 0.76 to 0.97 in 16 RCTs; 16 trials of 7637 women). This was not accompanied by a similar reduction in numbers of babies with low birthweight (RR 0.93, 95% CI 0.78 to 1.12; 14 trials of 5643 women). No significant differences were seen between the zinc and no zinc groups for any of the other primary maternal or neonatal outcomes, except for induction of labour in a single trial. No differing patterns were evident in the subgroups of women with low versus normal zinc and nutrition levels or in women who complied with their treatment versus those who did not.


CONCLUSIONS
The evidence for a 14% relative reduction in preterm birth for zinc compared with placebo was primarily represented by trials involving women of low income and this has some relevance in areas of high perinatal mortality. There was no convincing evidence that zinc supplementation during pregnancy results in other useful and important benefits. Since the preterm association could well reflect poor nutrition, studies to address ways of improving the overall nutritional status of populations in impoverished areas, rather than focusing on micronutrient and or zinc supplementation in isolation, should be an urgent priority.
Department of Health Policy, National Center for Child Health and Development, Tokyo, Japan.rintaromori@gmail.com.
Rintaro
R
Mori
Erika
E
Ota
Philippa
P
Middleton
Ruoyan
R
Tobe-Gai
Kassam
K
Mahomed
Zulfiqar A
ZA
Bhutta
D019587:Dietary Supplements; D005260:Female; D006801:Humans; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D011247:Pregnancy; D011256:Pregnancy Outcome; D047928:Premature Birth / Q000517:prevention & control*; D016032:Randomized Controlled Trials as Topic; D015032:Zinc / Q000008:administration & dosage*
D015032:Zinc