In a typical scenario, parents check in on their sleeping infant to find him or her dead. SIDS leave parents with a guilt and sadness that follows them throughout their lives.
"As a professional researcher, I have known a lot of parents whose babies have died of SIDS," said McEntire. "I don't think there is anything more devastating. You always feel responsible."
The cause of SIDS is unknown, although there are several theories.
Many doctors and researchers now believe that SIDS is not a single condition that is always caused by the same medical problems, but infant death caused by several different factors.
These factors may include problems with sleep arousal or an inability to sense a build-up of carbon dioxide in the blood. Almost all SIDS deaths occur without any warning or symptoms when the infant is thought to be sleeping.
SIDS is most likely to occur between 2 and 4 months of age, and 90 percent occur by 6 months of age, according to the Mayo Clinic.
Babies who are at increased risk are those who sleep on their stomachs, are exposed to cigarette smoke, sleep in the same bed as their parents or have soft crib bedding. Multiple birth and premature babies of those with a brother or sister who died of SIDS are also more vulnerable.
SIDS also affects boys more frequently than girls and can be linked to poverty or lack of prenatal care.
Alcohol use is now implicated because "anything that decreases parents' arousal increases the risk of SIDS," said researcher McEntire. "Don't sleep with the baby and definitely not when using alcohol or other drugs as sedatives.
"We are beginning to piece the puzzle together," she said. "We think most babies who die suddenly and unexpectedly with no known causes had a defect at birth, and [we] even think it's in the neurological system, in the part of the system that affects arousal, temperature control and blood pressure."
She points to the "triple risk model" to explain why some babies are more prone to SIDS: a genetic predisposition, exposure to an external situation [co-sleeping, blanketing] and being at a developmentally vulnerable age, under 1 year.
When babies are placed on their stomachs or if their faces are covered by bedding or if they sleep alongside a parent, they may rebreathe air, increasing carbon dioxide levels.
"Their arousal is not working right and they need to wake up, but they don't," said McEntire. "In and of itself, it's not a cause of death, but since we don't know which babies can safely sleep and which can't, we have to err on the side of safety."
The most important way to reduce risk is to make sure the baby has a "safe place to sleep."
Other big precautions include raising the baby in a smoke-free environment during pregnancy and beyond and putting babies to sleep on their backs with no crib cover, bumper pads or toys -- "nothing but the baby," said McEntire.