Understanding the Risks of Sudden Unexpected Death in Infancy


Published: 23 February 2023

Sudden unexpected death in infancy (SUDI) is the sudden and unexpected death of an apparently healthy baby within the first year of life (raisingchildren.net.au 2022).

SUDI can be categorised as either:

  • Fatal sleep accidents, which occur due to the infant being suffocated, trapped or strangled in their sleeping environment
  • Sudden infant death syndrome (SIDS) - unexplained deaths with no determined cause.

(raisingchildren.net.au 2022; Healthdirect 2020)

Although SUDI can occur whilst a baby is awake, most deaths occur whilst the baby is asleep, with a peak incidence between two and four months of age (Better Health Channel 2021).

In Australia, SUDI accounts for approximately 3 deaths out of every 10,000 births (raisingchildren.net.au 2022).

Predisposing Factors to Sudden Unexpected Death in Infancy

The exact cause of SUDI is unknown, and there are no consistent warning signs that it will occur (Better Health Channel 2021).

All infants are at general risk of SUDI; however, specific risk factors include:

  • Exposure to tobacco smoke or drugs in utero or after birth
  • Young age (two to four months)
  • Unsafe sleep environment
  • Premature birth
  • Being small at birth.

(Better Health Channel 2021; raisingchildren.net.au 2022)

The Triple Risk Model

The Triple Risk Model is based on the theory that SUDI is caused not by a ‘single characteristic that ordains an infant for death, but on an interaction of risk factors with variable probabilities’ (Bergman, as cited in Red Nose Australia 2021).

The Triple Risk Model suggests that in order for SUDI to occur, all three of the following conditions must be present at the same time:

  1. The infant must have an underlying vulnerability that predisposes them to SUDI. It’s unknown what exactly this vulnerability could be, but it’s theorised to involve defects in the parts of the brain that control respiration and heart rate, genetic factors, or a dysfunctional arousal mechanism.
  2. There also must be an external stressor. 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 the critical period of development, i.e. within the first year of life, particularly during the first six months.

(Red Nose Australia 2021)

It’s now generally accepted that SUDI is multifactorial in nature and that one risk factor alone is enough to cause death (Red Nose Australia 2021).

Safer Sleep Guidance

sudi infant lying in supine position
From birth, infants should always be placed on their backs to sleep, during both day and night.

Although SUDI is not always preventable, particularly in the case of underlying medical problems, providing a safe sleeping environment for the infant is the best way to reduce the risk of death (Healthdirect 2020).

This is because safe sleeping strategies aim to remove as many risk factors for SUDI as possible (Red Nose Australia 2021).

Ever since national awareness was brought SIDS risk factors in 1991, the rate of SIDS in Australia has decreased dramatically (AIHW 2022).

In fact, between 1980-1990, there was an average of 195.6 SIDS-related deaths per 100,000 births (d’Espaignet et al. 2007). As of 2017, this figure has dropped to 6 SIDS-related deaths per 100,000 births (AIHW 2022).

This is why following the safe sleep recommendations for infants is crucial.


  • From birth, always place the baby on their back to sleep, during both day and night. This reduces the risk of aspiration and helps to keep their airways clear
  • The baby should sleep next to their caregivers (in a separate bed) for the first 6 to 12 months of their life - this reduces the risk of SUDI by half
  • Ensure the baby’s cot meets Australian standards
  • Ensure the baby’s mattress is firm, flat and clean
  • Make sure the mattress properly fits the cot (so that the baby cannot become wedged between the mattress and the cot)
  • Maintain a smoke-free environment
  • Place the baby in the ‘feet to foot’ position, with their feet touching the end of the cot
  • Keep the baby's head uncovered with their blanket tucked in on three sides, no higher than chest level
  • If using a sleeping bag, ensure that it:
    • Is well-fitted across the neck and chest to prevent the baby from slipping inside the bag
    • Has sleeves or arm holes so that the baby can move their arms freely
    • Does not have a hood or head covering.

(Better Health Channel 2021; raisingchildren.net.au 2022; Healthdirect 2020)


  • Don’t sleep the baby on their stomach or side
  • Don’t sleep the baby with their face or head covered
  • Don’t dress the baby in excessive clothes, hats or beanies to sleep, as this can cause overheating
  • Don’t sleep the baby on a soft surface or couch
  • Don’t co-sleep (sleep on the same surface as the baby e.g. in the same bed)
  • Don’t sleep the baby where they could get wedged between the mattress and cot, or bed and wall
  • Don’t sleep the baby with loose or fluffy bedding
  • Don’t put any objects in the cot (e.g. pillows, soft toys, cot bumpers) as these can be hazards
  • Don’t fall asleep with the baby on a couch or chair
  • Don’t sleep with any other children or pets while the baby is sleeping in the same room.

(Better Health Channel 2021; raisingchildren.net.au 2022; Healthdirect 2020)

Do Pacifiers Reduce SIDS?

pacifier sudi
In Australia, the use of pacifiers is not actively encouraged nor discouraged.

There is evidence to suggest that the use of pacifiers is associated with a reduced risk of SUDI. However, the reason for this is not completely understood, and this has not been confirmed through a randomised control trial (Red Nose Australia 2018; RCHM 2020).

There are a variety of potential theories as to why pacifiers might reduce the risk of SUDI. These include:

  • Sucking on a pacifier keeps the tongue forward, which helps to maintain upper airway patency
  • Non-nutrient sucking reduces gastro-oesophageal reflux
  • Sucking on a pacifier decreases the arousal threshold
  • Infants are calmer when sucking on a pacifier and are, therefore, less likely to move around in their sleep
  • Pacifier handles are bulky and may prevent accidental hypoxia from the infant’s head being buried in soft bedding
  • Sucking on a pacifier might contribute to the development of neural pathways that control upper airway patency.

(Red Nose Australia 2018)

In Australia, the use of pacifiers is not actively encouraged nor discouraged. It’s up to caregivers to make an informed decision themselves after considering both the potential advantages and disadvantages of pacifier use (Red Nose Australia 2018; RCHM 2020).

If a pacifier is used, however, it’s recommended that for breastfed infants, pacifiers should only be introduced after breastfeeding has been established and phased out after one year (Red Nose Australia 2018; RCHM 2020).

The Psychological Impacts of Sudden Unexpected Death in Infancy

Losing a child suddenly and unexpectedly is a devastating experience that can have a severe psychological impact on the bereaved family. Feelings of guilt, anger, fear, blame and despair are common. Support from family, friends, healthcare professionals, counsellors and/or social workers will be extremely valuable. Some bereaved families may find it helpful to talk to other families who have lost an infant to SUDI (Better Health Channel 2021; raisingchildren.net.au 2022).

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 SUDI, such as exposure to cigarette smoke and potentially unsafe sleeping practices such as co-sleeping and bed-sharing.

Of course, when healthcare professionals 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.

Additional Resources



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Anne Watkins View profile
Anne is a freelance lecturer and medical writer at Mind Body Ink. She is a former midwife and nurse teacher with over 25 years’ experience working in the fields of healthcare, stress management and medical hypnosis. Her background includes working as a hospital midwife, Critical Care nurse, lecturer in Neonatal Intensive Care, and as a Clinical Nurse Specialist for a company making life support equipment. Anne has also studied many forms of complementary medicine and has extensive experience in the field of clinical hypnosis. She has a special interest in integrating complementary medicine into conventional healthcare settings and is currently an Associate Tutor, lecturing in Health Coaching and Medical Hypnosis at Exeter University in the UK. As a former Midwife, Anne has a natural passion for writing about fertility, pregnancy, birthing and baby care. Her recent publications include The Health Factor, Coach Yourself To Better Health and Positive Thinking For Kids. You can read more about her work at www.MindBodyInk.com.