Sudden Infant Death Syndrome

Authored by , Reviewed by Prof Cathy Jackson | Last edited | Meets Patient’s editorial guidelines

This article is for Medical Professionals

Professional Reference articles are designed for health professionals to use. They are written by UK doctors and based on research evidence, UK and European Guidelines. You may find the Sudden Infant Death (Cot Death) article more useful, or one of our other health articles.

Treatment of almost all medical conditions has been affected by the COVID-19 pandemic. NICE has issued rapid update guidelines in relation to many of these. This guidance is changing frequently. Please visit to see if there is temporary guidance issued by NICE in relation to the management of this condition, which may vary from the information given below.

Synonyms: cot death (especially amongst the general public), SIDS

Sudden infant death syndrome (SIDS) describes the sudden and unexplained death of a child under the age of 1 year. It is a tragic event which comes as a devastating shock to families involved.

SIDS is defined as the sudden and unexpected death of an infant under 1 year of age, apparently occurring during sleep, which remains unexplained after a thorough investigation including a complete autopsy and review of the circumstances of death.[1]All other possible causes of death must be excluded for this diagnosis to be made.

The terms 'sudden and unexpected infant death' (SUID) or 'sudden unexpected death in infancy' (SUDI) are sometimes used to describe all deaths, regardless of cause. Cases of SUID that remain unexplained after post-mortem examination and review of the history and circumstances surrounding the death are classified as SIDS. Around 80% of SUID cases are due to SIDS.[2]The remainder have a clear cause such as severe infection, inherited disorders of fatty acid oxidation or genetic cardiac channelopathies.

  • In the affluent West, SIDS is the most common cause of death of children between the ages of 1 month and 1 year. Almost 50% of deaths between these ages are due to SIDS.
  • In England and Wales in 2012, there were 221 deaths from SIDS. This is the equivalent of 0.3 deaths per 1,000 live births. In the UK as a whole there are around 270 deaths per year due to SIDS.
  • 8 out of 10 unexplained infant deaths occur between 28 days and 1 year (called the post-neonatal period.) The peak incidence is between 2 and 4 months of age.
  • Unexplained death is more common in male infants (64% of cases of SIDS were male infants in the UK in 2012).
  • In the UK, annual rates of deaths from SIDS are falling. The number of cases of SIDS in the UK almost halved between 1989 and 1992 when the 'Back to sleep' and 'Reduce the risks' campaigns were launched.

Although SIDS cannot be prevented, there are several factors which are known to be associated with increased risk. A 'Triple Risk Model' was proposed in 1994, emphasising the role and interaction of a number of factors in the pathogenesis of SIDS. In this model, SIDS occurs when three factors are present simultaneously. These factors are: an underlying vulnerability in the infant (eg, low birth weight or prematurity), a critical developmental period (usually 1-3 months of age) and an 'exogenous stressor' (eg, sleeping prone). It is thought that a combination of immature cardiorespiratory control systems and a failure to be roused from sleep lead to death.

Maternal smoking

A large number of studies have demonstrated consistently that maternal smoking during pregnancy increases the risk of SIDS by as much as five times. In one American study, 21% of all SIDS cases were attributable to maternal smoking.[5]

Passive exposure to smoke during infancy has also been shown to increase the risk. If both parents smoke, the risk is further increased.

Other maternal risk factors

Historically some other maternal features have been shown to be associated with an increased risk of SIDS. These include:[6]

  • Alcohol and substance abuse. This becomes a further issue when there is bed sharing with the infant (discussed below).
  • Age less than 20 at first pregnancy.
  • Poverty or lower socio-economic status.
  • Being single.

Preterm birth

Prematurity is associated with a four-fold increased risk of SIDS. This may be partly related to the fact that preterm babies are often placed prone whilst in special care baby units in order to improve respiratory function. It is important that they get used to sleeping on their back before discharge.

Other obstetric risk factors

  • Late or no antenatal care.
  • Low pregnancy weight gain.
  • Placental abnormalities. Such abnormalities may account for low birth weight, which is a risk factor for SIDS.

Sleep position

Prone sleeping is a major, modifiable risk factor and following campaigns to raise awareness of this, the numbers of cot deaths fell significantly. Placing babies on their backs to sleep is advice which should be reinforced by professionals. Reassure parents that the risk of aspiration is not increased by sleeping in this position and a number of studies have confirmed this.

Bed sharing

The issue of advising parents about sharing a bed with their baby is a potentially sensitive one and has received much prominence in the literature of late. Although it is a very common practice worldwide, there is emerging evidence that co-sleeping does increase the risk of SIDS.[7]Advice varies internationally. In the UK in 2014, the National Institute for Health and Care Excellence (NICE) updated its guidance to advise parents that sharing a bed with their baby is associated with an increased risk of SIDS.[8, 9] This risk is further increased for low birth-weight babies, when the adult sleeping with the baby has had alcohol or drugs and if either parent smokes.

Falling asleep with a baby in a sofa or armchair carries an even higher risk.

Department of Health and the Lullaby Trust (formerly the Foundation for the Study of Infant Deaths) advice is that the safest place for babies to sleep in the first six months of life is in a separate moses basket or cot, in the parental bedroom.[10] Room sharing is protective but bed sharing increases the risk.


Evidence shows that bedding has covered the infant's head in a significant number of deaths from SIDS. Soft bedding increases the risk of SIDS by five times and by much more if the baby is prone.

Therefore, advice to parents is:[10]

  • Duvets, quilts and pillows should not be used.
  • The baby's head should not be covered.
  • An infant sleeping bag is theoretically safer than blankets. However, where blankets are used, they should be thin and the infant should be placed with their feet at the foot of the cot. The blankets should be tucked in on three sides in such a way that they do not reach above the infant's armpits.
  • Mattresses should be firm.
  • Room temperature should be around 16-20°C and babies checked to make sure they feel a suitable temperature.

The following are associated with a reduced risk of SIDS:

  • Breast-feeding. Reduces risk and risk is further reduced if exclusively breast-feeding.[11]
  • Dummies.[12] There is consistent evidence that babies who die from SIDS are less likely to have used a dummy in their final sleep. However, advice varies, as dummies are thought to possibly reduce the length of breast-feeding time and therefore have other disadvantages. A Cochrane review failed to demonstrate that dummies do have a detrimental effect on breast-feeding, however.[13]
  • Room-sharing. A baby sleeping in the parental bedroom has a reduced risk of SIDS by possibly as much as 50%. Advice from the Lullaby Trust is therefore that babies should sleep in the parental bedroom (but not in the parental bed) for the first six months of life.[10]

The sudden death of a child is likely to be very traumatic for all concerned and that includes the attending doctor. Parents are likely to be in a state of shock and any professional attending in such a situation will need to be very sensitive and considerate in their handling of the family.

GPs are rarely likely to be involved in attending a sudden infant death but in the event of doing so, the following may be helpful:

  • When first looking at the infant, note the position in which the child is lying, the clothes the child is wearing, any secretions, etc on the child's face and make an accurate recording of these observations as soon as possible, so as to have contemporaneous notes.
  • Once it has been established that death has indeed taken place, the initial concern must be for the parent/s and other members of the family in attendance. After allowing a little time for them to accept the fact of the death, it must be gently explained to them that all cases of sudden death from any cause must be reported to the coroner or, in Scotland, the procurator fiscal, that police officers will call and that this is a routine process and not because of any suspicious circumstances.
  • Ask if there is anyone that you can call to come and stay with them, or look after siblings, particularly in the case of single parents.
  • The family of the child is likely to need support through the period of investigation and mourning and the death should be reported to their usual doctor and health visitor at the earliest opportunity.

Suggestions for GPs have been produced by the Lullaby Trust:

  • Don't avoid contact. Even a short phone call is appreciated.
  • Express your sympathy and sorrow and your availability for ongoing support. Ask if you can do anything immediately.
  • Use the baby's name.
  • Ensure the parent/s have the contact details of the Lullaby Trust for support and advice.
  • Avoid asking the parent/s to tell you about the event, unless they are keen to do so.
  • Avoid clichés and comparisons to other cases.

In approximately 37% of cases of sudden unexpected deaths in infancy, a post-mortem will identify a cause of death:[14]

  • Disease
  • Genetic disorder
  • Accidental injury
  • Non-accidental injury

Apparent life-threatening event syndrome used to be called near miss cot death. The term was dropped as there is NO evidence of association with or an increased risk of SIDS and the condition has different epidemiology. It is a presenting symptom, not a diagnosis.

  • It affects predominantly children younger than 1 year.
  • There are frightening symptoms with some combination of apnoea, change in colour, change in muscle tone, coughing or gagging.
  • Approximately 50% of these children are diagnosed with an underlying condition that explains the event.
  • The most common causes are gastro-oesophageal reflux, lower respiratory tract infections and seizures.
  • The cause remains unknown in around half.

The value of apnoea monitors is controversial, as they have not been proven to prevent SIDS. However, parents often feel reassured that they are 'doing everything they can', whilst using one.

There are a few cases, documented by covert video surveillance, in which parents have induced illness in their children. This can result in serious neurological damage and even death. The implications are discussed in the separate Fabricated or Induced Illness by Carers (FII) article.

There are occasions when more than one infant death occurs within a family and explanations are sought. There are three possibilities that immediately arise.

  • If SIDS is truly a random event then having more than one in a family is extremely bad luck. This does not mean that it cannot happen.
  • This has made people wonder if perhaps the children had been intentionally killed.
  • The third possibility is that there is a predisposition for SIDS that may run in some families and so it is not a random event.

The Care of the Next Infant (CONI) programme is available throughout most of the UK. All second infant deaths until 1990 were studied for one paper which reported:[17]

  • 57 infant deaths, giving a rate of 8.9 per 1,000 that is rather higher than would have been expected with no past history.
  • Of the deaths, 9 were inevitable, and 48 were unexpected.
  • Of the 48 unexpected deaths there were 2 in each of 2 families and a single one in the other 44.
  • Of the 46 first CONI deaths, 40 were natural but the other 6 were probable homicides.
  • There were 5 committed by one or both parents and 2 resulted in criminal conviction.

The conclusion is that repeat deaths occur and are usually natural but murder by parents does occur. However, some doubts were subsequently cast upon the method of classification of deaths as natural or unnatural in this report.[18]

SIDS cannot be prevented completely but experience shows that it can be reduced. This requires attention to the various risk factors outlined above. In particular, advice about placing the baby to sleep in the supine position in his/her parental bedroom and avoidance of parental smoking are important.

Supine sleeping position has, however, increased the incidence of flattening of the occiput (deformational plagiocephaly).[19]To try to prevent this, infants should have supervised 'tummy time' when awake - spending as much time as possible in the prone position.[20]The use of helmet therapy remains controversial.[21]

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Further reading and references

  1. Horne RS, Hauck FR, Moon RY; Sudden infant death syndrome and advice for safe sleeping. BMJ. 2015 Apr 28350:h1989. doi: 10.1136/bmj.h1989.

  2. Kinney HC, Thach BT; The sudden infant death syndrome. N Engl J Med. 2009 Aug 20361(8):795-805.

  3. Unexplained deaths in infancy. England and Wales, 2012; Office for National Statistics

  4. Shah T, Sullivan K, Carter J; Sudden infant death syndrome and reported maternal smoking during pregnancy. Am J Public Health. 2006 Oct96(10):1757-9.

  5. Highet AR, Goldwater PN; Maternal and perinatal risk factors for SIDS: a novel analysis utilizing pregnancy outcome data. Eur J Pediatr. 2013 Mar172(3):369-72. doi: 10.1007/s00431-012-1896-0. Epub 2012 Dec 4.

  6. Carpenter R, McGarvey C, Mitchell EA, et al; Bed sharing when parents do not smoke: is there a risk of SIDS? An individual level analysis of five major case-control studies. BMJ Open. 2013 May 283(5). pii: e002299. doi: 10.1136/bmjopen-2012-002299.

  7. Empowering families to make informed choices on co-sleeping with babies; NICE Press Release, 3 December 2014

  8. Postnatal care up to 8 weeks after birth; NICE Clinical Guideline (December 2014, updated February 2015)

  9. Sudden Infant Death Syndrome - A guide for professionals; The Lullaby Trust

  10. Hauck FR, Thompson JM, Tanabe KO, et al; Breastfeeding and reduced risk of sudden infant death syndrome: a meta-analysis. Pediatrics. 2011 Jul128(1):103-10. doi: 10.1542/peds.2010-3000. Epub 2011 Jun 13.

  11. Horne RS, Hauck FR, Moon RY, et al; Dummy (pacifier) use and sudden infant death syndrome: potential advantages and disadvantages. J Paediatr Child Health. 2014 Mar50(3):170-4. doi: 10.1111/jpc.12402.

  12. Jaafar SH, Jahanfar S, Angolkar M, et al; Effect of restricted pacifier use in breastfeeding term infants for increasing duration of breastfeeding. Cochrane Database Syst Rev. 2012 Jul 117:CD007202. doi: 10.1002/14651858.CD007202.pub3.

  13. Weber MA, Ashworth MT, Risdon RA, et al; The role of post-mortem investigations in determining the cause of sudden unexpected death in infancy. Arch Dis Child. 2008 Dec93(12):1048-53. Epub 2008 Jun 30.

  14. Hall KL, Zalman B; Evaluation and management of apparent life-threatening events in children. Am Fam Physician. 2005 Jun 1571(12):2301-8.

  15. Fu LY, Moon RY; Apparent life-threatening events: an update. Pediatr Rev. 2012 Aug33(8):361-8

  16. Carpenter RG, Waite A, Coombs RC, et al; Repeat sudden unexpected and unexplained infant deaths: natural or unnatural? Lancet. 2005 Jan 1-7365(9453):29-35.

  17. Bacon CJ, Braithwaite WY, Hey EN; Uncertainty in classification of repeat sudden unexpected infant deaths in Care of the Next Infant programme. BMJ. 2007 Jul 21335(7611):129-31.

  18. Orra S, Tadisina KK, Gharb BB, et al; The danger of posterior plagiocephaly. Eplasty. 2015 May 1215:ic26. eCollection 2015.

  19. Adams SM, Good MW, Defranco GM; Sudden infant death syndrome. Am Fam Physician. 2009 May 1579(10):870-4.

  20. Goh JL, Bauer DF, Durham SR, et al; Orthotic (helmet) therapy in the treatment of plagiocephaly. Neurosurg Focus. 2013 Oct35(4):E2. doi: 10.3171/2013.7.FOCUS13260.