Background: Magnesium maintenance therapy is one of the types of tocolytic therapy used after an episode of threatened preterm labour (usually treated with an initial dose of tocolytic therapy) in an attempt to prevent the onset of further preterm contractions.
Objectives: To assess whether magnesium maintenance therapy is effective in preventing preterm birth after the initial threatened preterm labour is arrested.
Search strategy: We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (May 2010).
Selection criteria: Randomised controlled trials of magnesium therapy given to women after threatened preterm labour.
Data collection and analysis: The review authors independently assessed the studies for inclusion, assessed risk of bias and carried out data extraction. We checked data entry.
Main results: We included four trials, which recruited 422 women. Three trials had high risk of bias and none included any long-term follow up of infants. No differences in the incidence of preterm birth or perinatal mortality were seen when magnesium maintenance therapy was compared with placebo or no treatment; or alternative therapies (ritodrine or terbutaline). The risk ratio (RR) for preterm birth (less than 37 weeks) for magnesium compared with placebo or no treatment was 1.05, 95% confidence interval (CI) 0.80 to 1.40 (two trials, 99 women); and 0.99, 95% CI 0.57 to 1.72 (2 trials, 100 women) for magnesium compared with alternative therapies. The RR for perinatal mortality for magnesium compared with placebo or no treatment was 5.00, 95% CI 0.25 to 99.16 (one trial, 50 infants) and also compared with alternative treatments, was 5.00, 95% CI 0.25 to 99.16 (one trial, 50 infants). Women taking magnesium preparations were less likely to report palpitations or tachycardia than women receiving alternative therapies (RR 0.26, 95% CI 0.13 to 0.52, three trials, 237 women) but were much more likely to experience diarrhoea (RR 7.66, 95% CI 2.18 to 26.98, three trials, 237 women).
Authors' conclusions: There is not enough evidence to show any difference between magnesium maintenance therapy compared with either placebo or no treatment, or alternative therapies (ritodrine or terbutaline) in preventing preterm birth after an episode of threatened preterm labour.