Giving magnesium maintenance therapy to women to prevent preterm birth after stopping threatened preterm labour

Magnesium does not reduce preterm birth or improve the outcome for the infant when given to women after contractions of preterm labour have been stopped.

Babies born preterm, before 37 weeks of pregnancy, may not survive or they may have later physical health and developmental problems if they do survive. Women whose preterm labour is stopped with tocolytic therapy (medication to reduce uterine contractions) remain at high risk of preterm birth. A variety of agents (tocolytics) are used to halt the uterine contractions. These include betamimetics, calcium channel blockers, magnesium sulphate, and oxytocin receptor antagonists. Subsequent tocolytic maintenance medication has been advocated. Oral and intravenous magnesium has been used to prevent further early contractions.

We included four randomised controlled trials involving a total of 422 women in this review. The trials did not demonstrate any differences between magnesium maintenance therapy and placebo or other treatments (ritodrine or terbutaline) in the prevention of preterm birth or perinatal deaths. The trials were too small to exclude either important benefits or harms from magnesium maintenance therapy. Magnesium was less likely than the alternative tocolytics (betamimetics) to result in side effects, particularly palpitations or tachycardia, although diarrhoea was more likely. This finding is based on very few studies of low quality, and none of them looked at the infants' later development.

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.

Read the full abstract...

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.


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 (31 January 2013).

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 involving 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 (two 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 5.00, 95% CI 0.25 to 99.16 (one trial, 50 infants) for magnesium compared with alternative treatments.

Women taking magnesium preparations were less likely to report side effects (RR 0.67, 95% CI 0.47 to 0.96, three trials, 237 women), including palpitations or tachycardia (RR 0.26, 95% CI 0.13 to 0.52, three trials, 237 women) than women receiving alternative therapies. Women receiving magnesium were however, more likely to experience diarrhoea (RR 6.79, 95% CI 1.26 to 36.72, three trials, 237 women).