Advances in neonatal science have made it possible to save some of the most delicate and prematurely born babies, but there is a potential downside. Preterm birth accounts for about a third of all cases of cerebral palsy, a developmental brain disorder that strikes 2 out of every 1,000 infants born in the United States. Some experts worry that as more and more preemies survive, rates of cerebral palsy will climb in lockstep.
"If we keep accelerating the rate at which we are able to save these very little babies, we are likely to see more cases of cerebral palsy, in which case we haven't saved them neurologically," says Dr. Deborah Hirtz, a pediatric neurologist at the National Institute of Neurological Disorders and Stroke.
But a new $25 million study, published Aug. 27 in the New England Journal of Medicine, suggests a familiar tool may help stem the tide. Researchers, including co-author Hirtz, found that when physicians gave an infusion of magnesium sulfate to women at imminent risk for preterm delivery between 24 and 31 weeks of gestation the odds of their infants later developing cerebral palsy dropped by almost half. The study, which took more than a decade to conduct, involved 2,241 women at an immediate risk of premature delivery, who were randomized to receive either intravenous magnesium sulfate or placebo in the hours before giving birth.
Nurses followed up with the mothers and babies for two years after birth. Moderate or severe cerebral palsy was later diagnosed in 41 children in the magnesium sulfate group (1.9%) compared with 74 children in the placebo group (3.5%). Because children with mild cerebral palsy can go on to enjoy near-normal lives, the study's primary outcome measure did not include those cases. The study's authors focused instead on moderate and severe cases most of these children will have disabilities serious enough to keep them from ever walking unassisted, says Dr. Dwight Rouse, director of the center for women's reproductive health at the University of Alabama at Birmingham and the study's lead author. "If we can prevent that outcome in only a few cases a year we will have done a tremendous thing," says Rouse.
The study authors hope the practice of giving magnesium sulfate infusions to women on the cusp of preterm delivery will catch on quickly because the drug is already a delivery room standby. "It's not a new medication or one that isn't already widely used," says Hirz. She compares it to aspirin in that it's "inexpensive, simple and not under patent." Magnesium sulfate essentially the stuff of Epsom salts is routinely used to delay labor and to prevent seizures in pregnant women with dangerously high blood pressure. "We probably give magnesium sulfate to 100 women to prevent one seizure," says Rouse. "With this, we just have to treat 64 women to prevent one case of moderate to severe cerebral palsy, which, unlike a seizure, is not going to go away."
Although the details regarding how exactly magnesium sulfate might prevent cerebral palsy are still uncertain, one theory is that the drug supports the baby's blood vessels. "Magnesium sulfate is known to stabilize vascular tone and, at some level, most brain injuries have to do with vascular instability," says Rouse. Cerebral palsy is caused by injury to the part of the brain that controls muscle movements. Though some children develop it after a head injury or brain infection, such as bacterial meningitis, the majority of cases occur just before birth, during delivery, or soon thereafter. "As an obstetrician, so often you feel like you have nothing to offer a woman facing this situation," says Dr. Catherine Spong, chief of the pregnancy and perinatology branch of the National Institute of Child Health and Human Development and one of the study's authors. "Now we can finally offer these mothers something that's potentially beneficial."