In the 1990s, there were several studies that suggested the benefits of magnesium sulfate in reducing neurological disorders associated with preterm births. But recent studies conducted by Australian scientists have found no association between exposure to magnesium sulfate in pregnant women and any neurological, behavioral, growth, or functional benefits in their children at school age. This study appears in JAMA, according to a press release.

Preterm babies are those who are born before 37 weeks of pregnancy. While there are different levels of risk associated with different stages of prematurity, babies born before 26 weeks are considered at most risk. The main factors that cause preterm labor are infection, gestational diabetes, multiple pregnancies, smoking, or family history.

Whatever the reason, doctors try their best to delay labor as much as possible, since preterm babies are a lot more at risk of hypothermia, low blood sugar, infection, and neurological disorders, such as cerebral palsy, than full term babies.

When doctors know that a woman is at risk of preterm delivery, she is given tocolytic therapy. This therapy delays labor at least for a few days, during which time doctors may administer other agents to improve the lung capacity of the infant. The most preferred tocolytic agent is magnesium sulfate, which was often used for its supposed neuroprotective effects for neonates born preterm. Previous research has shown that magnesium sulfate given to women who were expected to deliver preterm reduced the risk of cerebral palsy in surviving infants.

But these studies did not report about the mental and physical activity of preterm infants when they reached school. To identify later effects, Lex W. Doyle, of the University of Melbourne, Australia, and his team randomly assigned magnesium sulfate or a placebo to pregnant women (n = 535 magnesium; n = 527 placebo) for whom imminent birth was planned or expected before 30 weeks' gestation. Magnesium sulfate was given intravenously to these women. The trial was conducted in 16 centers in Australia and New Zealand.

At the time of randomization, 1,255 fetuses were alive. Of the 867 survivors available for follow-up tests, 669 were evaluated at school age, that is when they were 6 to 11 years old. The researchers found that receipt of antenatal (before birth)magnesium sulfate was not associated with any long-term benefits or harms compared with placebo on measures of neurological, cognitive, behavioral, growth, and functional outcomes.

Also, the total infant death rate did not differ significantly in the magnesium sulfate group. The authors are quick to point out that the absence of benefit does not negate the proven value of magnesium sulfate in reducing cerebral palsy, based on the collective evidence from all of the randomized clinical trials.

Although very premature babies constitute only a small percentage of all births, this number is growing and more infant death occurs from preterm-related problems than any other. With more than 500,000 babies being born preterm each year, more studies need to be conducted on the long-term effects of tocolytic agents like magnesium sulfate, say the researchers.

Source: Doyle LW, Anderson PJ, Haslam R, Lee KJ, Crowther C. School-age Outcomes of Very Preterm Infants After Antenatal Treatment With Magnesium Sulfate vs Placebo. JAMA. 2014.