TUESDAY, Dec. 13 (HealthDay News) -- Babies who are born prematurely are known to be at higher risk for Sudden Infant Death Syndrome (SIDS), and new research now suggests that's because their underdeveloped nervous systems can't control drops in blood pressure as needed during sleep.

SIDS is the sudden, unexpected death of an apparently healthy baby. The national Back-to-Sleep campaign, which encourages parents to place infants on their backs to sleep, has dramatically reduced the prevalence of SIDS. Still, more than 2,300 babies aged 1 month to 1 year die from SIDS in the United States each year, according to First Candle, a nonprofit group that raises awareness about SIDS.

In this latest study, Australian researchers conducted sleep testing on 25 preemies who were born at 28 to 32 weeks and 31 infants who were born full-term (between 38 and 42 weeks). They found that the baroreflex -- the system that regulates blood pressure -- does not mature as quickly in babies who are born too early. As a result, the baroreflex may not be able to compensate as quickly when there is a drop in blood pressure.

"Infants die during sleep because they fail to respond appropriately to a life-threatening situation such as a fall in blood pressure," explained study author Dr. Rosemary Horne, deputy director at the Ritchie Centre at the Monash Institute of Medical Research in Victoria, Australia.

Normally, "if there is a fall in blood pressure, heart rate will increase and the blood vessels will constrict to raise blood pressure," she said. "Conversely, if there is a surge in blood pressure, heart rate will fall and the blood vessels dilate to reduce blood pressure again."

But, this mechanism may not kick in as quickly in preemies, she said. There is no way to speed the maturity of this mechanism, but there are other things parents can do to help lower a premature infant's risk of SIDS, she said. These include placing the baby to sleep exclusively on his or her back, breast-feeding if possible and avoiding exposure to cigarette smoke. "It is particularly important that young babies are not sleeping with parents in the parental bed or on a sofa, as evidence now shows these practices to be significant risks for SIDS."

The study appears online Dec. 12 and in the January 2012 print issue of Pediatrics.

Dr. Rachel Y. Moon, director of academic development for the Goldberg Center for Community Pediatric Health at Children's National Medical Center in Washington, D.C., said that "preemies up to six months of age may be at higher risk for SIDS because their baroreflex is not as good and not as stable."

Do your best to eliminate any SIDS risks that are within your control, said Moon, who is a national expert on SIDS. "It is critical to try to give these babies every advantage they can get," she suggested, which includes placing them on their backs to sleep on a firm surface without blankets or anything that will cover their face. "Don't use pillows or bumper pads," she said. "Sometimes parents think they are doing the right thing, but they are unintentionally placing their infant in a more dangerous situation by surrounding him or her with pillows to keep them safe."

More information

First Candle has more on SIDS.