Your Health A-Z

Sudden Infant Death Syndrome (SIDS)

In the developed world SIDS is the commonest cause of death in infants between one week and one year of age.


  • Sudden infant death syndrome is also known as cot death
  • It occurs in all countries and socio-economic groups
  • A careful autopsy will fail to demonstrate an adequate cause of death in the majority of infants.
  • Infants between the ages of two and four months are most at risk
  • Smoking during pregnancy increases the risk
  • Risk factors have been identified. However, the cause is still unknown

What is sudden infant death syndrome (cot death)?

The sudden and unexpected death of a previously well infant is a tragedy known since biblical times. Commonly referred to as ‘cot or crib death’ or in the scientific literature as the sudden infant death syndrome (SIDS), Beckwith defined it in 1969 as ‘the death of an infant or young child, which is unexpected by history and in whom a thorough necroscopy examination fails to reveal an adequate cause of death’.

The classical belief was that these deaths were due to overlaying or suffocation – in fact the official title for the condition in the USA until the early 1950s was ‘accidental mechanical suffocation’.

We now know that this view is incorrect. In the developed world SIDS is the commonest cause of death in infants between one week and one year of age. It occurs in all countries and socio-economic groups, but rates vary widely, from well below one, to over six per thousand live births.

A careful autopsy will fail to demonstrate an adequate cause of death in the majority of infants. Many infants who die suddenly and unexpectedly, however, show changes indicative of a mild, ‘non-lethal’ respiratory or bowel infection. In a minority frank pathology will be found, such as pneumonia or meningitis, intracranial trauma or significant cardiac anomaly. In these cases death may indeed have been totally sudden and unexpected, but more often there have been prior symptoms which have not been recognised by the mother or caretaker.

What factors place an infant at greater risk?

Cot deaths are commonest between the ages of two and four months, but may occur in younger and much older infants. They are more common in poorer families, in crowded environments and in the winter months. Male infants are more often affected than females. Infants of low birth weight are at greater risk, as are multiple births. The ‘typical’ mother is young (below 25 years) and already has other young children. Later babies are more at risk than first-borns, and this risk increases with birth order.

Smoking during pregnancy increases the risk of cot death by a factor of two or three, and abuse of illegal drugs is associated with even higher rates. Studies of recurrence of SIDS in families in the USA, Norway and Sweden do not suggest that genetic factors play an important role.

What about the baby’s sleeping position?

There is clear evidence that the infant’s position during sleep is of importance. Studies from New Zealand, Australia, the UK, Holland, and Norway show an increased risk of SIDS in infants who sleep in the face down (prone) position. Since the supine or lateral sleeping position has been recommended, there have been significant decreases in incidence of cot deaths in many countries to less than one case per two thousand live births.

What about clothing and bedding?

Studies in New Zealand have provided evidence that over-heating may be a factor in some cases. When thick clothing and bedding are used, the infant’s head becomes the main route for heat loss. This could be compromised in the face down position, or when the baby’s head is covered by a sheet or blanket.

What is the cause of cot deaths?

Although the risk factors just discussed have been clearly identified, much remains to be learned about why these infants die. There have been hundreds of theories, and new ones are still appearing.

The most popular hypothesis is that they succumb during a period of extreme vulnerability when breathing control is in transition between the ‘foetal’ and the “adult”. Studies on infants who have been resuscitated from ‘near-miss’ episodes suggest that many such infants have poorly developed control of respiration similar to that seen in premature infants. Breathing during sleep is shallow and instead of regular breathing, a periodic pattern is seen with a tendency to prolonged pauses, called apnoea. It is believed that the most common mechanism of death in the SIDS victim is prolonged expiratory apnoea, the infant developing profound slowing of the heart, progressive lack of oxygen, a lowered blood pressure, and sinking irreversibly without a struggle.

In those with lesser degrees of impairment an added noxious stimulus may be required to precipitate apnoea. This could be a ‘mild’ viral infection, especially one causing upper or middle airway obstruction. It should be emphasised, however, that the great majority of babies dying of ‘cot death’ do so without any previously recognised apnoeic episodes, or abnormal breathing patterns.

There is, nevertheless, good evidence that a small minority of SIDS cases are due to a mixed bag of rare disorders. Great attention has recently been given to cardiac conduction disorders (prolonged QT interval). Other examples are infantile botulism, inborn errors of metabolism, certain disorders of respiratory control and filicide (non-accidental injury).

Some controversies

In many African and Asian cultures, it is normal practice for the infant to sleep close to the mother in the same bed (co-sleeping). Whether this is a risk factor for SIDS or actually protective remains an important, but as yet unanswered question.

While unintentional suffocation or overlaying of the infant by the mother or another person does occasionally occur, this is generally on an unsuitable sleeping environment such as a sofa. Often the adult is obese, or alcohol or drugs are involved. Infants may also occasionally be strangulated by the bars of a cot or by cords in clothing or bedding. However, suffocation of the infant has been repeatedly rejected as a major cause of SIDS.

SIDS rates are actually lowest in Asian communities where co-sleeping is the norm. Parental sleep contact provides constant stimulation to the infant through vocalisations, body movements, radiant heat, and respiratory sounds. In fact infants who share the parents’ bed exhibit synchronous arousal and co-ordination of sleep stages with the parent. Some researchers therefore consider that parent-infant contact throughout the night may help some vulnerable infants to override the deficits that result in SIDS.

Toxic gases
Most controversial is the hypothesis that gases emitted by plastics could accumulate and rise to levels toxic to the infant. Richardson (1994) published experimental evidence that fungi present in or on old mattresses could generate the poisonous gases stibine, arsine or phosphine, from the elements antimony, arsenic and phosphate, often present in plastic materials. Sprott pointed out that many of the risk factors associated with SIDS could be explained on this environmental basis.

He mounted a campaign in New Zealand to promote the use of impermeable polythene mattress covers to prevent egress of toxic cases, and claims that no infant sleeping on such a mattress had died of SIDS (Sprott 1996). The experimental evidence on which this hypothesis is based has been disputed (Limerick Final Report 1998).

Non-accidental injury
Before recognition of sudden infant death as an entity, many parents were wrongly accused of killing their infants either deliberately or accidentally. Recently the role of wilful suffocation has again come to the fore as a factor in some cases. It must be realized that it is difficult to distinguish post-mortem between sudden death and smothering by a soft pillow and undoubtedly instances of infanticide do occur in this fashion. Nevertheless, awareness of this possibility must not be allowed to interfere with the sympathetic approach to shocked and grief-stricken parents, the overwhelming majority of whom are totally innocent.

Is immunisation linked with SIDS?
A number of studies have shown that immunisation does not increase the risk of SIDS, and in fact may be protective.

The commonly held belief that breastfeeding is protective against SIDS has been negated in several studies, but the many advantages of breastfeeding need no emphasis. It is the mothers who are socially at risk of SIDS who would be least likely to breastfeed in first world settings.

How common are cot deaths?

Since recommendations about sleeping position have been widely propagated, SIDS rates have fallen in Europe and Australasia to a level of 0,5 per thousand live births, or less. Regional comparisons of SIDS incidence rates have limitations, because autopsies by expert pathologists are seldom available, particularly in Third World countries. Some insist that a death scene examination or review must be included to exclude accidents, infant neglect or abuse before a death can be certified as SIDS. It is not surprising then that in southern Africa, and in developing countries generally, the incidence of SIDS is difficult to establish.

In a Cape Town study of deaths below the age of four years reported in 1989, the respective incidences of SIDS were 1,06 per 1000 live births for whites, rising to 3,41 for coloured infants. At that time black infants could not be included in the study due to difficulties with home visiting. A more recent prospective study from Zimbabwe reported an incidence of only 0,2 per thousand in a black township community, and South African statistical data also show a relative risk for black infants which is only one third that of white.

How can cot deaths be prevented?

  • ‘Put your baby on the back to sleep’. The prone (face down) sleeping position should be avoided; from birth infants should be put to sleep on their sides or back, unless there are specific indications against this. Sleeping on their backs appears to be preferable to side sleeping, because of the greater likelihood of the infant rolling face down when on the side.
  • ‘Make sure your baby’s head remains uncovered during sleep and avoid overheating and tight wrapping’.
  • ‘Keep your baby smoke free – before birth and after’. Mothers should be warned of the dangers of smoking and drug taking.
  • ‘Cover the mattress with polythene sheeting’. Many new mattresses are fitted with such covering; used mattresses should be wrapped in a sheet of thick polythene (125 microns) which is folded and taped underneath. The evidence for toxic gases is still incomplete, but the practice has been shown to be safe, and is recommended in the UK and New Zealand. The best underblanket to use on a wrapped mattress is fleecy cotton.
  • You should sleep in the same room as your baby. To lessen the risk of cot death it may be safer for the infant to sleep in the parent’s room. ‘For babies to endure increasingly long periods of solitude after birth is biologically unreasonable’.
  • It would also seem entirely reasonable biologically for the young infant to sleep in close proximity to its mother, and perhaps this is actually protective. The evidence suggests that there may be potential benefits to bed sharing which cannot be overlooked. This aspect requires further study in communities where co-sleeping is common.

‘Near miss’ episodes

Brief spells of stopping breathing or a few seconds of ineffectual breathing due to airway closure are commonly seen in normal infants during sleep. More prolonged attacks, and especially those associated with pallor, blueness or a long recovery period are more important.

With increased public awareness, such ‘acute life-threatening events’ – ALTE’s – have become a common problem for paediatricians, but the great majority of such reported episodes are benign and simply represent normal sleep pauses or brief choking spells. It should be stressed that in the majority of cot deaths there is NO antecedent history of such events. Nevertheless any such episode MUST be fully investigated by an expert; in particular an electrocardiograph must be performed to rule out a conduction disorder of the heart, such as the ‘long QT’ syndrome.

What to do in the event of a sudden infant death

There is a special poignancy in the tragedy of a cot death. The parents are generally young and may have had no prior contact with death. The mother is in a particularly vulnerable period emotionally following pregnancy and puerperium. Great happiness and elation over the normally healthy baby is transmuted overnight into shock, bewilderment and guilt. Often lack of understanding of the nature of cot deaths and confusion with child abuse lead to stigmatisation of the parents. Death-shy society tends to shun them just when the greatest support is needed.

Mothers vary in the extent of their reaction to such a tragedy. Some seem to be well adjusted initially and may suffer much longer with the internal suppression of their grief. There may be psychosomatic symptoms such as aching in the arms or hallucinations of hearing the baby crying. Such manifestations often decrease with time, but there may be occurrences of feelings of isolation and remorse for months and years afterwards, engendered by anniversaries or recollections of the dead child, often long after sympathetic support has been withdrawn by those about her.

Psychological reactions are not confined to the mother. The father may also suffer severe disturbance and be badly affected by the loss. There have been many instances of serious family disruption and divorce as a result of cot deaths. Siblings too may show behavioural expressions of loss and insecurity, such as reversion to infantile behaviour, bed wetting at night and nightmares.

It has been found that an unhurried visit by a doctor or health visitor a week or so after the infant’s death will allow parents to unburden themselves. They need to ventilate all their imagined errors of omission or commission which they feel may have contributed to the child’s death, and thus mitigate feelings of guilt.

Contact with those who have suffered similar tragedies can be a major source of support. Parents should be put in touch with a Cot Death Society, if available, or other appropriate resources.

(Written by Prof M Kibel, Emeritus Professor of Child Health)

The information provided in this article was correct at the time of publishing. At Mediclinic we endeavour to provide our patients and readers with accurate and reliable information, which is why we continually review and update our content. However, due to the dynamic nature of clinical information and medicine, some information may from time to time become outdated prior to revision.

In the interest of our patients, in accordance with SA law and our commitment to expertise, Mediclinic cannot subscribe to the practice of online diagnosis. Please consult a medical professional for specific medical advice. If you have any major concerns, please see your doctor for an assessment. If you have any cause for concern, your GP will be able to direct you to the appropriate specialists.