Magnesium sulphate for preventing preterm birth in threatened preterm labour

BACKGROUND: Magnesium sulphate is used to inhibit uterine activity in women in preterm labour to prevent preterm birth. OBJECTIVES: To assess the effectiveness and safety of magnesium sulphate therapy given to women in threatened preterm labour with the aim of preventing preterm birth and its sequelae. SEARCH STRATEGY: We searched the Cochrane Pregnancy and Childbirth Group trials register (May 2002) and the Cochrane Controlled Trials Register (The Cochrane Library, Issue 2, 2002). SELECTION CRITERIA: Types of participants: Women thought to be in preterm labour. Types of interventions: Magnesium sulphate as the only tocolytic, administered intravenously or orally, compared with either placebo, no treatment or alternative tocolytic therapy. Types of outcome measures: Measures of effectiveness, complications, women's satisfaction with their care and health service use. DATA COLLECTION AND ANALYSIS: Assessments of trial eligibility, quality and data extractions were done by at least two of the reviewers. MAIN RESULTS: Over 2000 women were recruited into the 23 included trials. Only nine trials were rated of high quality for the concealment of allocation. In the magnesium sulphate versus control (all studies) no difference was seen for the risk of birth within 48 hours of treatment for women given magnesium sulphate compared with controls when using a random effects model (relative risk (RR) 0.85, 95% confidence interval (CI) 0.58-1.25, 11 trials, 881 women). No benefit was seen for magnesium sulphate on the risk of giving birth preterm (<37 weeks) or very preterm (<34 weeks). The risk of death (fetal and paediatric) was higher for infants exposed to magnesium sulphate (RR 2.82, 95% CI 1.20-6.62, 7 trials, 727 infants). There were only two fetal deaths, both in the magnesium sulphate group in one study. The six other trials reported there were no fetal deaths. No differences for total paediatric mortality were shown in the six trials with data. No beneficial effect was seen from using magnesium sulphate on the risk of other neonatal morbidity. A non-significant reduction in the risk of cerebral palsy was reported at follow up at 18 months corrected age (RR 0.14, 95% CI 0.01-2.60, 1 trial, 99 children). AUTHORS' CONCLUSIONS: Magnesium sulphate is ineffective at delaying birth or preventing preterm birth, and its use is associated with an increased mortality for the infant. Any further trials should be of high quality, large enough to assess serious morbidity and mortality, compare different dose regimens, and provide neurodevelopmental status of the child.