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Premature babies routinely get powerful steroids both before and after they are born. The drugs help the babies' tiny lungs mature and boost blood pressure, among other benefits. Previous research in animals found the drugs can affect brain development. Now, a new study confirms similar effects in human babies.

Caring for premature babies requires a careful balancing act. On the one hand,preemies are at risk for a variety of medical problems. But their tiny, developing bodies are ultra sensitive to side effects from important medicines they may need.

Researcher Emily Tam, MD, of the University of California-San Francisco explains that animal studies found that the steroids called glucocorticoids affect a certain part of the brain.

"The cerebellum is particularly targeted, resulting in cell death and decreased cell growth," Tam says. "And so, the question then is, is this same thing happening in humans?"

The cerebellum is involved in motor control and some cognitive functions, among other things, so it plays a critical role in an infant's first years.

In a study, 172 premature babies born in the United States and Canada got MRI scans to measure their cerebellums. Tam says researchers found no adverse affects from steroids given to the pregnant mothers before birth.

"On the other hand," Tam says, "we did find that when hydrocortisone and dexamethasone were given after the child was born, this was associated with decreased growth of cerebellum. So by term age, the cerebellum was 10 percent smaller that it should have been."

The findings present doctors with a real quandary. The steroids are given because they help preemies’ breathing and blood circulation, which are obviously important. But the reduced cerebellum size was seen even in babies given very small doses of the glucocorticoids.

"Low doses of these drugs are not without risks. And when considering the different drug options, they should look at other options first."

Tam says her team plans to continue the study of these premature babies to see if those with smaller cerebellums are more likely to have any developmental issues as they grow up.

Emily Tam and her collegues published their research in the journal Science Translational Medicine.

steroid: 類固醇；激素類

preemie: 早產嬰兒

glucocorticoid: 糖皮質激素

cerebellum: 小腦

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（來源：VOA 編輯：Rosy）