The next time your baby cries, listen closely -- it could tell you if your child is at risk of sudden infant death syndrome, a new study suggests.
Boston researchers found that in more than 21,000 healthy newborns, unique differences in the way some babies cried made them up to 32 times more likely to die of SIDS than the other infants.
The frequency of a baby's cry could be the most significant risk factor found for SIDS thus far, according to the study's authors.
In the study, Dr. Michael Corwin and colleagues at Boston City Hospital audiotaped the cries of the infants, then used high-tech computer software to break down the various acoustic components of the cries.
They found that babies whose wails exhibited a high first formant -- the first frequency of sound that is modified by the airway -- during the first week of life had 3 1/2 times the normal risk of dying from SIDS.
In a second round of taping, if a baby's cry had a high first formant again, the risk of dying from SIDS was nine times higher than average, the scientists reported in the July issue of the journal Pediatrics.
In babies whose cries had periodic frequency changes as well as high first formants, the risk rose to 32 times the normal risk, they found.
Twelve babies in the study, all of whom were considered to be at DTC low risk of SIDS, died from the disorder. All had cries that had a high first formant, the researchers said.
SIDS is the sudden, unexplained death of an infant under age 1. It is the leading cause of death in babies 1 week to 1 year old in the United States, where the current rate of SIDS is about one case per every 1,000 births.
The study results may explain reported instances in which parents whose babies had died of SIDS thought their infants' cries sounded different from those of healthy babies, Dr. Corwin said.
"It is much less accurate, but in some cases a parent might be able to detect a difference," said Dr. Bradley Thach, a professor of pediatrics at the Washington University School of Medicine in St. Louis.
Dr. Thach said these differences in SIDS babies' cries may signify abnormal control of the muscles around the throat, which could cause closure of the airway during sleep.
While cry analysis is not ready to be used as a general screening tool, it could be available in the near future, according to Marian Willinger of the pregnancy and neonatology branch at the National Institute of Child Health and Development.
"To date, this is the most powerful tool yet for identifying infants at high risk of SIDS," she said. "But to have a screen for every baby, we need another marker" that would identify SIDS risk, such as variations in heart rate.