SIDS, or Sudden Infant Death Syndrome, is a tragic cause of death in which an infant less than 1 year of age dies unexpectedly and without a medical explanation for their death. It's a terrifying syndrome, to say the least. So, how many babies die of SIDS now compared to the past in the United States? SIDS rates have declined throughout the years.

According to the National Institutes of Health, SIDS rates significantly declined in the 1990s, with the largest decline shown between 1992 to 1999. From 1994 to 1999, SIDS reportedly declined by 50 percent, and rates of back sleeping more than doubled, NIH stated.

But apparently, the exact rates and statistics of SIDS may be affected by different classifications for cause of death throughout the years. The NIH study found that Accidental Suffocation or Strangulation in Bed (ASSB) have alternatively shown increases throughout the years, which could be skewing the reported decreasing numbers of SIDS because it's classified differently:

While SIDS rates were declining and then stabilizing, rates of other sleep-related causes of infant death—such as 'accidental suffocation or strangulation in bed (ASSB)'—were increasing. Several recent studies suggest that much of the decrease in SIDS rates since 1999 might be explained by changes in classification9 of cause of death. Some deaths that were once classified as SIDS were now being classified as other causes of death, such as accidental suffocation or other ill-defined and unspecified causes.

According to the Centers for Disease Control and Prevention, about 3,500 infants in the United States die suddenly and unexpectedly each year. The CDC classifies SUID, or Sudden Unexpected Infant Death, as the all encompassing term for infants who die unexpectedly and suddenly, with SIDS, ASSB, and "Unknown Cause" as specific classifications. In 2014, the CDC reported that 1,500 babies died from SIDS specifically.

Here are a few examples of cause of death factors for how the CDC distinguishes ASSB from SIDS:

"Mechanisms that lead to accidental suffocation include":

Suffocation by soft bedding—for example, when a pillow or waterbed mattress covers an infant's nose and mouth.
Overlay—for example, when another person rolls on top of or against the infant while sleeping.
Wedging or entrapment—for example, when an infant is wedged between two objects such as a mattress and wall, bed frame, or furniture.
Strangulation—for example, when an infant’s head and neck become caught between crib railings.

The CDC provides charts and graphs that show reported death rates of SIDS from 1990 to 2014. During that time frame, SIDS rates declined from 130.3 deaths per 100,000 live births in 1990, to 38.7 deaths per 100,000 live births in 2014.

Parents and caregivers can access information on SIDS and prevention guidelines on the CDC's website.