WEDNESDAY, Aug. 27 (HealthDay News) -- Magnesium sulfate, given to mothers at risk of preterm delivery, cut the rate of cerebral palsy in their babies by nearly half, a new study found.

"If deemed to be at high or immediate risk of delivery prior to 32 weeks, women and their doctors should consider using magnesium sulfate to prevent their child from having cerebral palsy," said study lead author Dr. Dwight J. Rouse, a professor of obstetrics and gynecology at the University of Alabama at Birmingham.

The findings are published in the Aug. 28 issue of the New England Journal of Medicine.

But in an editorial accompanying the study, other experts called for caution and more study before routinely recommending the treatment to prevent cerebral palsy.

In the study, the largest of its kind, Rouse and his colleagues randomly assigned 2,241 women at risk of delivering early -- between 24 and 31 weeks -- to receive either magnesium sulfate or a placebo. (Babies born after 37 to 42 weeks of pregnancy are considered full term, according to the March of Dimes.) The magnesium sulfate was given intravenously as the women entered labor as a 6-gram dose followed by a constant infusion of 2 grams per hour until either 12 hours had passed, labor had subsided, or they had given birth.

The researchers then compared infants born to each group of mothers to see if there were differences in the rates of death or the occurrence of cerebral palsy.

Cerebral palsy, marked by abnormal movement control and postures that cause limited activity, is caused by damage or dysfunction to the developing fetal or infant brain. Preterm birth is itself a risk factor for the condition. About one third of cerebral palsy cases are associated with preterm birth.

In past studies, magnesium sulfate hasn't borne out as an effective treatment for delay of early labor. But it has proven effective for treatment of maternal high blood pressure associated with pregnancy, Rouse said.

And some previous research had found magnesium sulfate effective for reducing the risk of cerebral palsy, but other studies had been inconclusive. So, Rouse and his colleagues embarked on this large, more comprehensive study.

They found no significant differences in the proportion of deaths between the magnesium sulfate group and the placebo group. But they did find that moderate or severe cerebral palsy was diagnosed in just 1.9 percent of the group treated with magnesium sulfate, compared to 3.5 percent in the placebo group.

Rouse said it's not known for certain how the compound may work. But, he said, it may "stabilize the vessels in the vulnerable preterm brain," protect against damage from lack of oxygen, and guard against injury caused by swelling and inflammation.

"Our findings are applicable only to early preterm birth," he added. "We define high risk as threatening delivery prior to 32 weeks."

Dr. William Zinser is a pediatric neurologist at Children's Medical Center, Dallas, and an associate professor of pediatric neurology at the University of Texas Southwestern Medical Center. He said, "It's too early to know if magnesium sulfate has an overall effect on the incidence rate of cerebral palsy."

Zinser reviewed the study but was not involved with it. "More research needs to be done, certainly," he said.

Rouse said women at risk for preterm birth should discuss the potential use of magnesium sulfate with their doctors.

More information

To learn more about preterm birth, visit the March of Dimes.