SIDS – A Comprehensive Guide to Risk Factors

Sudden Infant Death Syndrome (SIDS) is every parent’s worst nightmare. SIDS is when you put your healthy baby to sleep only to find it lifeless, without any apparent cause of death. As the birth of my first baby was just around the corner, I wanted to do some research about the risk factors of SIDS.

SIDS is a subcategory of Sudden Unexpected Infant Death (SUID). That is a term which describes any unexpected and sudden death of an infant. It includes both explained and unexplained deaths.

Data by the US Center for Disease Control and Prevention (CDC) has shown that there were 3,700 SUID cases in the United States in 2015. The cases pertain to infants younger than one year, and whose deaths showed no obvious cause. Furthermore, cases of SUID branch out into several subcategories. These include SIDS, an unknown cause and accidental suffocation in bed.

According to the data by CDC and the National Center for Health Statistics (NCHS), SIDS accounted for 1,600 deaths in the US in 2015. For the sake of comparison, 1,200 deaths were a result of an unknown cause. At the same time, there were 900 cases of accidental suffocation. This means that around 43% of all SUID cases belonged to the category of SIDS. Data issued by the National Center for Health Statistics specify that SIDS, along with suffocation and other unintentional injuries take place 81 times in every 100,000 live births.

The most recent research published by NICHD (Eunice Kennedy Shriver National Institute of Child Health and Human Development) covered data up until 2013. It pinpoints SIDS as the predominant cause of death of babies aged between one month and one year. Furthermore, it states that SIDS affects boys slightly more than girls. The majority of cases included in this research have shown that death due to SIDS mostly occurs between the child’s age of 1 month and 4 months. A vast majority of cases (up to 90%) occurs before the age of 6 months.

SIDS can be defined as a sudden death of an infant under the age of 1, which comes unexpectedly given the child’s medical history. Also, each death due to SIDS remains unexplained following an autopsy and thorough investigation of all factors involved. A  2016 publication by the American Academy of Pediatrics covers this topic, among others. Its full title: SIDS and Other Sleep-Related Infant Deaths: Updated 2016 Recommendations for a Safe Infant Sleeping Environment.

Risk Factors

In most of the cases, Sudden Infant Death Syndrome occurs during sleep. At times, SIDS is referred to as “cot death” or “crib death” given the period when it mostly occurs. Cribs, as such, have no place in the conversation about the risk factors. However, the baby’s sleep surroundings can play a vital role.

With all the research undertaken in previous decades, there is now a somewhat clearer picture with regard to risk factors.

Of course, this topic has been much researched and debated. The diagnostic category of SIDS was only introduced as recently as 1969. Throughout the years, medical experts have pointed at several factors that can lead to sudden death of infants.

A Pediatrics Journal study from 2014 also showed that the age of a baby plays a role in determining the risk factors contributing to SIDS.

The study found that most of the children younger than 4 months who died in their sleep were co-sleeping (bed sharing). As for the children older than 4 months, a risk factor that was established was sleeping on their stomach or surrounded by pillows, blankets or stuffed toys.

The authors took into account the unexplained deaths of 8,207 babies in 24 US states in the 2004-2012 period.

First of all, it should be noted that cases of babies dying in their sleep are more frequent in younger infants. Namely, with babies older than 6 months, the risk decreases.

As for how it happens: in the majority of cases, it seems that death occurs when a baby, in its sleep, stops breathing. However, it then fails to awake and change its position.

Research has indicated the possibility that infants who sleep on their stomach fall into a deeper sleep. This means that in case of obstructed airways, for whichever reason, it could make it more difficult for them to wake up. Also, research has shown that SIDS is almost up to 20 times more likely to occur in babies who usually sleep on their backs and who somehow switch during the night and end up on their stomachs.

Another risk factor linked to a baby’s sleeping habit is co-sleeping. Namely, much of the infants stricken with SIDS have slept beside an adult.

However, those two forms of sleeping habits have not been singled out as the only factors contributing to SIDS. In addition, research has established that among babies who die of SIDS, there are cases of children who were vulnerable in a certain way. For instance, not being able to awaken quickly, maybe due to lacking brain receptors that would normally react to arousal chemicals.

One of the issues the 2014 research particularly highlighted is the changing of the risk factors with age. Namely, the 2014 Pediatrics Journal study found that 70% of the babies who died of SIDS were up to three months old. Out of that number, three in four babies did not sleep by themselves when they died.

As for babies older than 3 months, it was more likely for them to be found on their stomachs. Also, as mentioned before, it is common in such cases that a baby is found surrounded by a pillow, stuffed animal or blanket. Sleeping on soft surfaces, such as a couch, regular mattresses, or other spaces other than cribs can also raise the risk of SIDS. Finally, a considerable percentage of infants (18%) had changed their sleeping position before SIDS had occurred. Namely, they had switched from their side or back to their stomach.

This data indicates that the age and sleeping patterns are not the only issues contributing to the risk factors. The infant’s stage of development is to be taken into account, as well.

That in mind, it is important to put a baby on its back to sleep, as well as to avoid co-sleeping, if possible. Finally, the space in which the baby sleeps should be kept tidy. That means that the crib should be without objects such as the aforementioned ones. All of that lowers the risk of the baby ending up on its stomach.

A paper published back in 2011 highlighted the so-called triple-risk model for SIDS. It combines intrinsic risk factors, extrinsic risk factors and the baby’s age, i.e., critical development period. The first group includes factors such as male gender, prematurity and prenatal exposure to tobacco and/or alcohol. The second one refers to co-sleeping, sleeping on the side and sleeping on an overly soft surface. The triple-risk model originated back in 1994. It coincided with the American “Back-to-Sleep” public campaign which urged parents to place their children on their backs to sleep.

Also, research has highlighted some disparity in terms of SIDS rates when it comes to ethnic and racial groups. Statistics published by Georgetown University’s National Center for Education in Maternal and Child Health illustrate this. Even though they pertain to the period up until 2010, data indicates that the SIDS rate was much higher among, for instance, non-Hispanic Blacks and American Indian/Alaska Natives.

Other situations that generally increase the risk of SIDS are smoking during pregnancy or after birth. This pertains to smoking in the baby’s surroundings. Also, all situations in which the adult caretaker of the baby is under the influence of alcohol and/or tired.

Research, in general, has singled out regular breastfeeding as a positive measure to reduce the risk of SIDS.


International Statistics

As for international data on SIDS, there is a lack of data concerning the most recent period. However, statistics covering the timeframe up until 2005 confirm an overall sharp decline in SIDS rates compared with the 1990s.

British organization The Lullaby Trust which aims to prevent unexpected infant deaths recently published data pertaining to 2015. It comes via the Office of National Statistics, and specifies, for instance, that around 232 infants die of SIDS every year in the UK. It also echoes the findings according to which premature babies are more prone to SIDS. Interestingly, this research also states that the risk of SIDS is up to 3 times higher in babies whose parents are younger than 20.


Summary and Quick Facts*

  • It is possible for SIDS to set in anytime during the first year of the baby. However, it is most likely to happen between month 1 and 4 – up to 72% of cases.
  • In more than 90% of cases, SIDS will affect babies younger than 6 months.
  • The risk declines after the eighth month. Still, parents are advised to carry out preventive measures well until the twelfth month.

*Data source: Technical Report of the American Academy of Pediatrics,Task Force on Sudden Infant Death Syndrome, conveyed by the NICHD at this link.



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