Sudden infant death syndrome

Synonyms: cot death (especially amongst the general public)

Overview

What is sudden infant death syndrome?

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.

Sudden infant death syndrome 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. All other possible causes of death must be excluded for this diagnosis to be made.¹

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 sudden infant death syndrome. The remainder have a clear cause such as severe infection, inherited disorders of fatty acid oxidation or genetic cardiac channelopathies.

Whilst the pathogenesis of SIDS is not yet fully elucidated, there is evidence that an important subset of SIDS infants have serotonergic abnormalities resulting from a problem in the medullary reticular formation which is comprised of nuclei that contain serotonin neurons. This lesion could lead to a failure of protective brainstem responses to homeostatic challenges during sleep in a critical developmental period which cause sleep-related sudden death. This is known as the serotonin brainstem hypothesis.²³

• In the Western hemisphere sudden infant death syndrome is the most common cause of death of children between the ages of 1 month and 1 year.

• In England and Wales in 2023:

  • There were 164 unexplained deaths of infants, of which 52% were due to SIDS. This is similar to recent years.

  • Male and female infants were equally as likely to have an unexplained death, the first year for which this has been the case since 2017 - in all the intervening years there was a male predominance.

• Since 2004, the sudden infant death mortality rate has halved to 0.16 deaths per 1,000 live births in 2019, due to public information campaigns aimed at ending prone sleeping for infants.

Although sudden infant death syndrome 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.

• 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 and SIDS⁵⁶

• Maternal smoking is a risk factor for sudden infant death syndrome - SIDS is more frequently observed in infants of smoking mothers.

• The level of risk due to smoking is dose-dependent and 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^{1 4}

Historically some other maternal features have been shown to be associated with an increased risk of sudden infant death syndrome. These include:

• 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.

• No supportive relationship.

• Low birthweight.

• Age under 4 months.

• The mother having 2 or more previous children.

Preterm birth

Prematurity is associated with a four-fold increased risk of sudden infant death syndrome. 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.⁷ Placing babies on their backs to sleep is advice which should be reinforced by professionals. Parents should be reassured that the risk of aspiration is not increased by sleeping in this position and a number of studies have confirmed this.

Bed-sharing⁸⁹

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 when the parents smoke or have drunk alcohol that day. The evidence about co-sleeping when there are no other risk factors (such as cigarettes or alcohol) is more variable, with some reviews suggesting that the risk persists and others that it does not. Falling asleep on a chair or sofa with a baby is more dangerous than bed sharing.

The National Institute for Health and Care Excellence (NICE) guidance on postnatal care, updated in 2021,¹⁰ did not make a blanket recommendation against bed sharing - it included two recommendations in this area:

• Discuss with parents safer practices for bed sharing, including:

  • Making sure the baby sleeps on a firm, flat mattress, lying face up (rather than face down or on their side)

  • Not sleeping on a sofa or chair with the baby.

  • Not having pillows or duvets near the baby

  • Not having other children or pets in the bed when sharing a bed with a baby.

• Strongly advise parents not to share a bed with their baby if their baby was low birth weight or if either parent:

  • Has had 2 or more units of alcohol.

  • Smokes.

  • Has taken medicine that causes drowsiness.

  • Has used recreational drugs.

The 2022 NICE quality statement on postnatal care ¹¹ also advises that parents should be given advice about safer practices for bed sharing, rather than advising against the practice in all cases.

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.¹² They also have a resource for patients which contains advice about bed sharing. ¹³It covers many of the same points as the NICE guidance and also advises that bed sharing is less safe if the baby was premature.

Bedding

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

Therefore, advice to parents is: ¹²

• 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 sudden infant death syndrome: ¹

• Breastfeeding. Reduces risk; risk is further reduced if exclusively breastfeeding, compared to partial breastfeeding. ¹⁴

• Dummies. 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 breastfeeding time and therefore have other disadvantages. A Cochrane review failed to demonstrate that dummies have either a positive or a detrimental effect on risk of SIDS, but a US task force concluded that there is a protective effect. The studies on which they based this conclusion were largely done some years before the Cochrane review.¹⁵¹⁶

• 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.

The sudden death of a child is very traumatic for all concerned, including the attending doctor. Parents will be in a state of shock and any professional attending will need to be 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, and 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 to 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 include:

• 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 some cases of sudden unexpected deaths in infancy, a post-mortem will identify a cause of death:¹⁷¹⁸

• Disease

• Genetic disorder

• Accidental injury

• Safe-guarding issues

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 sudden infant death syndrome. 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. Siblings of SIDS infants have an increased risk of dying as a result of SIDS. Siblings are 5-6 times more likely than the general population to die from SIDS.¹ After investigation, not all sibling deaths can be attributed to SIDS. Sibling deaths have also been found to be attributable to inborn errors of metabolism, abuse, and malnourishment.

The Care of the Next Infant (CONI) programme is available throughout most of the UK. It provides specialist support to parents who have lost an infant to SIDS, throughout their next pregnancy and for the first six months after their next baby is born. ¹⁹

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 the infant's parental bedroom and avoidance of parental smoking are important.

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