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, may not survive or they may have later physical health and developmental problems if they do survive. Women whose preterm labor is stopped with tocolytic therapy 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 sulfate, and oxytocin receptor antagonists. Subsequent tocolytic maintenance medication has been advocated. Oral magnesium has been used to prevent further early contractions. We identified four randomised controlled trials involving a total of 422 women for 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, and none of them looked at the infants' later development.