Sudden Infant Death Syndrome

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

Sudden infant death syndrome (SIDS) describes the sudden and unexplained death of a child under the age of one year old.

It is a diagnosis of exclusion and can be made only after detailed history with examination of the site of death and post mortem examination. All other possible causes of death must be excluded for this diagnosis to be tenable.¹ It usually occurs in apparently healthy children during sleep with no warning.

In the affluent west, SIDS is the most common cause of death of children between the ages of 1 month and 1 year of age, with the majority of the deaths occurring between the ages of 4 and 6 months.

• In 1996 the incidence in England and Wales was 0.9 per 1,000 live births.
• By 1998 and 1999 this figure had fallen to 0.45 per 1,000.² Boys are more often affected than girls, representing about 60% of cases.
• The commonest season is the winter and the commonest time is early morning. This may be related to changing sleep patterns as the infant matures and biological clocks.³
• Over the last decade, due to a greater understanding of the risk factors associated with SIDS and particularly the risk of the infant sleeping in a prone position, the number of SIDS deaths has declined significantly.

Although sudden infant death syndrome cannot be prevented, there are several factors which are known to be associated with increased risk.

Maternal factors

• Smoking during and/or after pregnancy:
  • In an American study,⁴ of all SIDS cases, 21% were attributable to maternal smoking whilst among smokers, 61% of SIDS cases were attributable to maternal smoking.
  • Maternal smoking during pregnancy is associated with a significantly increased risk of SIDS.
  • There is even a relationship between maternal smoking and changes in the brainstem of the infant.⁵
• Late or no ante-natal care
• Low pregnancy weight gain
• Age less than 20 at first pregnancy
• Placental abnormalities
• Alcohol and substance abuse
• History of sexually transmitted disease

Infant factors

• Overheating during sleep:
  • There is an association with high tog factor bedding and clothes.⁶
  • Sleeping in the prone position (on the front).⁷ Infant BP is modified by sleep state and sleeping position.⁸ A tendency for BP to fall in the prone position appears to be prevented by elevating the heart rate at 2-4 weeks and 5-6 months, but not at 2-3 months, coincident with the age of greatest risk for SIDS. An uncompensated fall in BP in the prone position at this age could increase the possibility of circulatory failure and SIDS in vulnerable infants.
  • Both high tog bedding and sleeping in a position other than on the back may contribute to the high risk associated with bed sharing.⁶
• Exposure to cigarette smoke in utero or after birth.
• Family history of SIDS.
• Many other factors have been thought to influence the development of SIDS, including type of bedding and mattress, bottle feeding and the use of a "dummy". The evidence is not so strong although soft bedding may predispose to asphyxiation.

Sometimes SIDS will follow an immunisation. This is inevitable as infant vaccination schedules occur at the same time as the peak age for SIDS. However, there is no increased risk after vaccination⁹ and the figures may even suggest a slight but insignificant protection. Children regarded as high risk for SIDS should have their immunisation schedule as usual.

Some feel that the large yield of post-mortem bacteriological cultures positive for S. aureus and E. coli, in otherwise unexplained cases of SIDS, suggests that these bacteria could be associated with this condition.¹⁰

The sudden death of a child is likely to be very traumatic for all concerned, and that includes the attending doctor. Useful guidelines for GPs have been produced by the Foundation for the Study of Infant Deaths.¹¹ 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.

• When first looking at the infant, note the position in which the child is lying, 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 parents 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 procurator fiscal in Scotland, 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.
• Many parents, on finding their baby lifeless will have attempted some form of resuscitation, or will have removed the child from the site of death to attempt to get help and a detailed history of events will need to be taken using open questions such as " can you tell me what happened?" " had the baby been ill recently?". Further detailed questioning will be undertaken by the police officers, who will also perform a detailed examination of the site of death, and again it is important to reassure parents that this, together with a post mortem examination, is a routine process in order to ascertain the cause of death, and not due to any suspicion of foul play.
• The family of the child are 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.
• Sometimes, a lone mother in particular, will be fearful that the father will blame her for the death of the baby. This will be a special problem if there is a history of domestic violence.
• The family are likely to have a number of questions in the ensuing weeks and months including "Why did it happen?" "Is it likely to happen to any future children?" "Is there anything we could have done to prevent the death?" and should be given the opportunity to ask these questions and given information on local and national agencies who are able to provide information for grieving families.

In approximately 37% of cases, a post mortem will identify a cause of death:¹²

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

It is now widely believed that infants that are affected by SIDS are born with a predisposition which makes them more vulnerable to physiological stresses, and current research is focussing on identifying subtle abnormalities in the brain and brainstem, particularly in those areas responsible for the control of breathing and heart rate.¹³

Although this has been known for several years,¹⁴ more recent research¹⁵ has suggested that the role of serotonin and its deficiency in the possible pathogenesis of SIDS is more important than had previously been realised. This may also help to explain the vulnerability of boys. It may also explain some susceptibility of families.

Apparent life-threatening event syndrome used to be called near miss cot death:

• It affects predominantly children younger than one 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 problems are digestive (up to 50%), neurological (30%), respiratory (20%), cardiac (5%), and endocrine or metabolic (<5%).
• The cause remains unknown in around half.¹⁶
• These children do appear to be at greater risk of developing SIDS although most cases are benign.¹⁷

The value of apnoea monitors is controversial but at least they will assure the parents that "everything is being done".

There are a few cases, documented by covert video surveillance, in which parents have induced illness in their children.¹⁸ This can result in serious neurological damage and even death. The implications are discussed in Munchausen Syndrome by Proxy. In an English study of 150 cases,¹⁹ there were 18 incidents of parents deliberately suffocating the child and 7 of Munchausen syndrome by proxy.

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. The chance of winning the National Lottery is 1 in 14 million but at least one person does it most weeks. If the risk of SIDS is, say, 1 in 2,000, the risk of loosing both of 2 children is 1 in 4 million (2,000²) and the chance of loosing all of 3 is 1 in 8 billion (2,000³).
• This has made people wonder if perhaps the children had been intentionally killed.
• The third possibility is that there is a predisposition for SIDS than may run in some families and so it is not a random event.

An English study examined cases of recurrent unexpected infant death:²⁰

• They studied 57 deaths.
• There had been 2 deaths in 24 families and 3 deaths in 3 families.
• Post mortem examination explained 11 deaths (19%).
• They thought that 7 (12%) were accidental.
• They thought that 31 (55%) were most probably due to an action by one of the parents (filicide or murder).
• Only 5 (9%) were considered to be true or idiopathic sudden infant death syndrome.
• In 3 (5%) cases there was insufficient information to draw a conclusion. There was serious social deprivation in 5 (18%) of the families.
• A history of psychiatric illness was present in one or both parents in 18 (67%) of the families.

A more recent paper looked at the subject again, based on the CONI (care of the next infant) programme that is available throughout most of the UK:²¹

• There were 57 infant deaths, giving a rate of 8.9 per 1000 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.

There have been a number of high profile court cases in which mothers have been convicted of killing their babies but they have strenuously protested their innocence. In some, the basis of conviction was expert testimony to the effect that recurrent cases of SIDS are so rare that there must be an alternative explanation. This expert evidence has since been discredited.

In one appeal the mother of the convicted woman was brought over from Bangladesh to testify how she had lost 7 of her 10 children to unexplained infant death.

There had obviously been a serious miscarriage of justice in several cases and some people try to use this to discredit all the work of Professor Roy Meadow, including his covert surveillance to prove Munchausen syndrome by proxy.

Doctors must be meticulous and open-minded when working as expert witnesses, especially in such crucial matters but it is important not to let those with a grudge dismiss a great deal of important and conscientious work. Parents do harm their children. Sometimes they kill them but most of the time they are very caring and conscientious. If there is one thing worse than loosing a baby, it is then to be convicted of killing that baby.

The concept that a mother may kill her baby has long been accepted in law, especially if she is of unsound mind after childbirth. Thus a lower offence of infanticide may be found if the baby is less than 1 year and 1 day old. No one other than the baby's mother can claim that defence.

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, placing the baby to sleep on the back and avoidance of smoking are important.