Miscarriage is a common complication of pregnancy that can be caused by a wide range of factors. Poor dietary intake of vitamins has been associated with an increased risk of miscarriage, therefore supplementing women with vitamins either prior to or in early pregnancy may help prevent miscarriage.

Objectives
The objectives of this review are to determine the effectiveness and safety of any vitamin supplementation, on the risk of spontaneous miscarriage, maternal adverse outcomes and fetal and infant adverse outcomes.

Search strategy
We searched the Cochrane Pregnancy and Childbirth Group Trials Register (8 September 2004), the Cochrane Central Register of Controlled Trials (The Cochrane Library, Issue 2, 2003) and MEDLINE (1966 to May 2003), Current Contents (1998 to May 2003) and EMBASE (1980 to May 2003).

Selection criteria
All randomised and quasi-randomised trials comparing one or more vitamins with either placebo, other vitamins, no vitamins or other interventions, prior to conception, periconceptionally or in early pregnancy (less than 20 weeks’ gestation).

Data collection and analysis
Two review authors independently assessed trials for inclusion, extracted data and assessed trial quality.

Main results
We identified seventeen trials assessing supplementation with any vitamin(s) starting prior to 20 weeks’ gestation and reporting at least one primary outcome that were eligible for the review. Overall, the included trials involved 35,812 women and 37,353 pregnancies. Two trials were cluster randomised and contributed data for 20,758 women and 22,299 pregnancies in total. No difference was seen between women taking any vitamins compared with controls for total fetal loss (relative risk (RR) 1.05, 95% confidence interval (CI) 0.95 to 1.15), early or late miscarriage (RR 1.08, 95% CI 0.95 to 1.24) or stillbirth (RR 0.85, 95% CI 0.63 to 1.14) and most of the other primary outcomes, using fixed-effect models. For the other primary outcomes, women given any type of vitamin(s) compared with controls were less likely to develop pre-eclampsia (RR 0.68, 95% CI 0.54 to 0.85, four trials, 5580 women) and more likely to have a multiple pregnancy (RR 1.38, 95% CI 1.12 to 1.70, three trials, 20,986 women).

Authors’ conclusions
Taking vitamin supplements, alone or in combination with other vitamins, prior to pregnancy or in early pregnancy, does not prevent women experiencing miscarriage or stillbirth. However, women taking vitamin supplements may be less likely to develop pre-eclampsia and more likely to have a multiple pregnancy.

Plain language summary
Supplementing women with any vitamins, alone or in combination with other vitamins, does not reduce the number of women who miscarry or have a stillbirth

Poor diet, without enough vitamins, has been associated with an increased risk of women losing their baby in early pregnancy. Taking vitamin supplements prior to pregnancy or in early pregnancy may reduce the risk of miscarriage, but this review did not find this to be the case. However, women taking vitamin supplements may be less likely to develop pre-eclampsia and more likely to have a multiple pregnancy. More research is needed.

A Rumbold, P Middleton, CA Crowther

Cochrane Database of Systematic Reviews 2007 Issue 4
DOI: 10.1002/14651858.CD004073.pub2   This version first published online: 20 April 2005 in Issue 2, 2005
Date of Most Recent Substantive Amendment: 2 February 2005

This record should be cited as: Rumbold A, Middleton P, Crowther CA. Vitamin supplementation for preventing miscarriage. Cochrane Database of Systematic Reviews 2005, Issue 2. Art. No.: CD004073. DOI: 10.1002/14651858.CD004073.pub2.