Understanding the Risks of Sudden Infant Death Syndrome


Published: 26 February 2020

Sudden infant death syndrome (SIDS), also known as ‘cot death’ is the sudden, unexpected and unexplained death of an apparently healthy baby within the first year of life.

About 20% of sudden and unexpected infant deaths (SUID) have a clear cause, including severe and unequivocal infection.

The other 80% that remains unexplained after a thorough investigation of the circumstances of death and post-mortem results are classified as SIDS (Kinney and Thach 2009).

Although SIDS can occur whilst a baby is awake, most deaths occur whilst the baby is asleep, with a peak incidence between one and four months old (Psaila et al. 2017).

In the UK it’s thought that more than 200 babies die suddenly and unexpectedly each year (NHS 2018), whilst in Australia, approximately 100 deaths are reported annually (Horne 2019).

Although SIDS can occur whilst a baby is awake, most deaths occur whilst the baby is asleep.

Predisposing Factors

Despite the success of prevention campaigns, SIDS remains a leading cause of infant mortality and the search for preventable risk factors continues.

As Goldwater (2003) comments, it’s generally accepted that low birth weight and premature babies are at greater risk of SIDS, with slightly more cases noted in boys compared to girls.

The list of factors thought to be associated with SIDS is extensive, some of them can be avoided but many cannot. For example:

Prenatal and Pregnancy Risk Factors

  • Higher parity;
  • Low birth weight;
  • Short gestation;
  • Intrauterine growth retardation;
  • Inadequate prenatal care;
  • Maternal smoking;
  • Smoking within the household during pregnancy;
  • Maternal recreational drug use;
  • Urinary tract infection.

Demographic and Genetic Risk Factors

  • Lower socioeconomic status;
  • Age at death peaking at 2-4 months;
  • Male babies;
  • Cold weather.

Neonatal and Postnatal Risk Factors

  • Passive exposure to cigarette smoke;
  • Lack of breastfeeding;
  • Prone sleep position;
  • Bed-sharing or sofa sleeping;
  • Used mattress;
  • Lack of, or late immunisation.

(Goldwater 2003)

The Triple Risk Factor

Current evidence suggests that SIDS involves a convergence of stressors that can result in asphyxia in a vulnerable infant.

As Kinney and Thach (2009) explain, SIDS occurs when there is ‘a simultaneous juxtaposition of multiple events that, when taken individually, are far less powerful than the result of their chance combination’.

Current evidence suggests that SIDS involves a convergence of stressors that can result in asphyxia in a vulnerable infant.

Building on this idea of multiple factors interacting together to cause SIDS, Degnan (2013) suggests the triple-risk model, first described in 1994 can be used to identify the most vulnerable infants.

The three risk factors are:

  1. The infant must have an underlying vulnerability that predisposes them to SIDS.
  2. There also must be stress from an exogenous source. For example, asphyxia associated with a prone sleeping position and airway compression, or impaired cardio-respiratory regulation related to heat stress.
  3. These stressors must occur during a critical period of development i.e. the first 12 months of life.

Some of the strongest evidence about reducing the risks of SIDS relates to safe sleep guidance and the use of pacifiers.

Safer Sleep Guidance

Carpenter et al. (2013) point out that the risks associated with bed-sharing are greatly increased when combined with parental smoking, maternal alcohol consumption or drug use.

They also suggest that a substantial reduction in the number of SIDS cases could be achieved if parents avoided bed-sharing.

Risks can also be considerably reduced by making sure new parents have a good understanding of the following guidelines related to safe sleeping:


  • Place babies on their back to sleep, both day and night as this can reduce the risk of SIDS up to six times compared to laying them on their front.
  • Practice room sharing for the first six months as this can halve the risk of SIDS.
  • Maintain a smoke-free environment. Around 60% of sudden infant deaths could be avoided if babies weren’t exposed to smoke during pregnancy or around the home.
  • Place babies in the ‘feet to foot’ position, with their feet touching the end of the cot, Moses basket, or pram.
  • Keep the baby's head uncovered with their blanket tucked in no higher than their shoulders.


  • Don’t co-sleep with your baby if you or your partner have been drinking, or if either partner smokes or has been taking drugs or is extremely tired.
  • Don’t fall asleep on the sofa with your baby, it can increase the chance of SIDS by up to 50 times.

Bates (2014) makes the point that the incidence of SIDS has decreased by about 70% since the 1990s, largely due to the understanding that babies are much safer when placed on their back to sleep.

It’s a point worth noting as many grandparents or older relatives may unwittingly pass on unsafe advice about laying babies to sleep face down, or on their sides.

Do Pacifiers Reduce SIDS?

Psalia et al. (2017) ask the question: ‘Does the use of infant pacifiers reduce the risk of sudden infant death syndrome?’

They go on to suggest that whilst in their opinion there is no evidence pacifiers work, neither are there any well-designed trials, suggesting that more research is needed before a definitive answer is found.

Hauck (2005) on the other hand, conducted case-control studies demonstrating a significant reduction in the incidence of SIDS with pacifier use, particularly when used for both daytime and nighttime sleep.

For breastfed infants, pacifiers should be introduced after breastfeeding has been well established and continued for up to a year which includes the peak ages for SIDS risk and the period in which the infant's need for sucking is strongest.

Pacifiers should be introduced after breastfeeding has been well established and continued for up to a year.

Practice Points

Midwives, nursery nurses, health visitors and other maternity care staff are in an ideal position to educate and influence parenting practices.

As Bredemeyer (2004) says, there are many opportunities from antenatal care to postnatal check-ups for midwives to set an example and reinforce the message about the use of the supine position when laying a baby down to sleep.

Parental education should also include information about environmental factors that are known to increase the risk of SIDS, such as exposure to cigarette smoke and other potentially unsafe sleeping practices such as co-sleeping and bed-sharing.

Of course, when health visitors and midwives talk to new parents the last thing they want to think about is SIDS.

It’s a scary topic that can be difficult to talk about but as Bates (2014) states, after over 40 years of research, we now know how to significantly reduce the risk of it happening and how to keep babies safer.