THURSDAY, Dec. 18 (HealthDay News) -- Pregnant women at risk of preterm delivery who are given multiple doses of steroids to help their fetus tend to give birth to low birth-weight babies with smaller head circumference, a new study found.

A single dose of corticosteroids had been the standard of care for many years to reduce the chances of infant mortality, respiratory distress syndrome, and bleeding in the brain. And, it was thought that women who remained at risk of preterm birth after an initial dose would benefit from repeated doses.

"A single course of steroids is given to all women at risk of preterm birth, and that still holds," said study lead author Dr. Kellie E. Murphy, who's with Mount Sinai Hospital's Department of Obstetrics and Gynaecology, in Toronto, Canada.

"The results of this trial will change clinical practice worldwide," she said. "It will conclusively stop practitioners from giving multiple courses of antenatal corticosteroids."

The report was published in the Dec. 20/27 issue of The Lancet.

Dr. William F. Walsh, chief of nurseries and a specialist in the care of high-risk newborn babies at Vanderbilt University Medical Center in Nashville, said clinical practice has already changed, and most doctors only give a single dose of steroids.

"Every research has shown an overwhelming benefit from one course of steroids for premature babies," he said, adding that multiple doses are no better than one.

"It's an important question to answer, but I thought it had already been answered," Walsh said.

For the new research, Murphy and her colleagues studied 1,858 women at 25 to 32 weeks of gestation who had not delivered their babies within 14 to 21 days after receiving one dose of corticosteroids.

The women were randomly assigned to corticosteroids every 14 days until 33 weeks of gestation or until they delivered, or a placebo. The researchers looked for cases of death before or after delivery and other conditions, such as severe respiratory distress syndrome and bleeding in the brain.

Murphy's team found that women given multiple doses of corticosteroids had babies that weighed less, were shorter and had smaller head circumference than babies of mothers given a placebo.

Also, there was no difference in other results, such as death, respiratory problems and bleeding in the brain between the babies of women given more than one dose of steroids and women given a placebo, the researchers reported.

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