Article: Sudden infant death syndrome

Sudden infant death syndrome (SIDS) is any sudden and unexplained death of an apparently healthy infant aged one month to one year. The term cot death is sometimes used in the United Kingdom, and crib death in North America.

Diagnosis

SIDS is a definition of exclusion and should only apply to an infant whose death is sudden and unexpected, and remains unexplained after the performance of an adequate postmortem investigation including (1) an autopsy, (2) investigation of the scene and circumstances of the death and (3) exploration of the medical history of the infant and family. Generally, but not always, the infant is found dead after having been put to sleep and exhibits no signs of having suffered.

The inexplicability of SIDS often leaves the parents with a deep sense of guilt in addition to their grief.

Statistics

SIDS is responsible for roughly 50 deaths per 100,000 births in the US. It is responsible for far fewer deaths than congenital disorders and disorders related to short gestation; though it becomes the leading cause of death in otherwise healthy babies after one month of age.

The frequency of SIDS appears to be a strong function of infant gender (61% male) and the age, race, education, and socio-economic status of the parents.

Risk factors

Very little is known for sure about the possible causes of SIDS; there is no proven method for absolute prevention. Listed below are several factors associated with increased probability of the syndrome.

Prenatal risks

• inadequate prenatal care
• inadequate prenatal nutrition
• tobacco smoking
• use of heroin
• teenage pregnancy
• less than a one year interval between subsequent births

Post-natal risks

• low birth weight (especially less than 1.5 kg (~3.3 lbs)
• exposure to tobacco smoke
• laying an infant to sleep on his or her stomach (see positional plagiocephaly)
• failure to breastfeed
• excess clothing and overheating
• excess bedding, soft sleep surface and stuffed animals
• gender (61% of SIDS occur in males)
• age (incidence rises from zero at birth, is highest between 2-4 months and goes towards zero at one year)

Research on co-sleeping indicates an excess risk with an adjusted Odds-Ratio of 2.71 (Vennemann et al., Acta Paediatr. 2005 Jun;94(6):655-60.) There is a good deal of debate and discussion in the medical literature about this (see below). For example, though findings are still preliminary and unpublished, the proximity of a parent's respiration is thought by some to stimulate proper respiratory development in the infant. It is interesting to note that the first epidemiologic investigation of sudden unexpected infant deaths by Templeman in Dundee in 1892 were shown to be probably from suffocation by overlaying (Williams et al., Sudden unexpected infant deaths in Dundee, 1882-1891: overlying or SIDS? Scott Med J. 2001 Apr;46(2):43-7).

(The use of baby monitors, particularly those with motion sensors, can allow the parents to remotely keep track of their child.)

SIDS and child abuse

The neutrality of this article is disputed. Please see the discussion on the talk page.

British paediatrician Roy Meadow believes that many cases diagnosed as SIDS are really the result of child abuse on the part of a parent displaying Munchausen Syndrome by Proxy (a condition which he was first to describe, in 1977). During the 1990s and early 2000s, a great many mothers of multiple apparent SIDS victims were convicted of murder (English law) on the basis of Meadow's opinion. However, in 2003 a number of high-profile acquittals brought Sir Roy's theories into disrepute, and many now doubt their credibility. Several hundred murder convictions were reviewed, almost all attracting no new action. BBC TV presenter Anne Diamond has been responsible for raising awareness of causing cot death in the UK.

On the other hand, in a 6 March 2004 incident, a father is being accused of the murders of four of his children, one of which had been ruled a case of SIDS[1], and the National Clearinghouse on Child Abuse and Neglect Information indicates more than half of fatal child abuse cases may be unreported or described as SIDS.

A mathematical discussion of the errors in Roy Meadow's analysis is presented here by Professor Ray Streater of King's College London. This also includes this link to an "unprecedented intervention" by the Royal Statistical Society.

Possible nitrogen dioxide link

A recent study by researchers at the University of California, San Diego suggests a link between nitrogen dioxide (NO₂) levels and SIDS (Klonoff-Cohen et al., Outdoor carbon monoxide, nitrogen dioxide, and sudden infant death syndrome. Arch Dis Child. 2005 Jul;90(7):750-3). However, this is only one of many possible risk factors and cannot be causal.

Conditions that may mimic SIDS

Medium Chain Acyl Dehydrogenase (MCAD) deficiency, infant botulism and long-QT syndrome.

Prevention

Though SIDS cannot be prevented absolutely, parents of infants are encouraged by pediatricians and popular parenting books to take several precautions in order to reduce the likelihood of SIDS.

Sleep position

Place the infant on its back to sleep. Among the theories supporting this habit is the idea that the small infants with little or no control of their heads may, while face down, inhale their exhaled breath or smother themselves on their bedding. Another theory states that babies sleep more soundly when placed on their stomachs, and are unable to rouse themselves when they have an incidence of sleep apnea (e.g., breath-holding, which is thought to be common in infants).

Only use a firm mattress with well fitted (tight) sheets in a crib or bassinet. No pillows, stuffed animals, or fluffy bedding should be used or placed in a crib. In cold weather dress the infant warmly in well fitted clothing. Wearable blankets are preferable over loose blankets. These directions also stem from the belief that small babies with little or no control of their bodies may inadvertently smother themselves in their sleep.

Sleep sacks

In colder environments where bedding is required to maintain a baby's body temperature the use of a sleep sack is becoming more popular. A study published in the European Journal of Pediatrics in August 1998 [2] has shown the protective effects of a sleep sack as reducing the incidence of turning from back to front during sleep, reinforcing putting a baby to sleep on their back for placement into the sleep sack and preventing bedding from coming up over the face which leads to increased temperature and carbon dioxide rebreathing. They conclude in their study "The use of a sleeping-sack should be particularly promoted for infants with a low birth weight."

Breastfeeding

A study published in the May 2003 issue of Pediatrics [3] revealed that breastfeeding infants have 1/5 the rate of SIDS as formula-fed infants. Two other studies supported breastfeeding for reducing SIDS rates:

• Hoffman, H.J., "Risk Factors for SIDS: Results of the National Institute of Child Health and Human Development SIDS Cooperative Epidemiologic Study". Ann NY ACAD Sci, 1988.
• Mitchell, A. "Results from the First Year of The New Zealand Count Death Study". N.Z. Med A, 1991; 104:71-76

Co-sleeping

A controversial approach to lowering SIDS rates is co-sleeping. Although a 2005 policy statement by the American Academy of Pediatrics on sleep environment and the risk of SIDS condemned all co-sleeping and bedsharing as unsafe, empirical data[4] has suggested that almost all SIDS deaths in adult beds occur when other prevention methods, such as placing the infant on his back, are not used. Infant deaths in adult beds are also reduced when parents are non-smoking, not impaired by drugs or alcohol, not obese, and are not using fluffy comforters and pillows. A firm sleeping surface is also required, which rules out waterbeds or soft mattresses. With these factors accounted for, SIDS rates for co-sleeping infants are actually lower than for crib-sleeping infants. Parents also have newer room and bedsharing options including bed side and bedtop sleeping devices to make co-sleeping safer and more convenient.

A 2005 study states that "sleeping with an attentive, unimpaired mother is not only safe but biologically sound" (McKenna JJ, McDade T. Why babies should never sleep alone: a review of the co-sleeping controversy in relation to SIDS, bedsharing and breast feeding. Paediatr Respir Rev 2005;6:134-52. PMID 15911459). The practice of solitary sleep for infants leads, among other things, to an absence of exogenous stimuli that influence breathing, cardiovascular function, and sleep architecture in the sleeping infant. Sleep and waking states and state transitions are apparently produced by suites of state regulatory mechanisms that function as a dynamical system. Modeling of dynamical systems has demonstrated that they are organized, or “tweaked” by episodic, irregular inputs. Some investigators (Mosko et al., 1993; McKenna, 1996) have argued that cosleeping provides infants with stimuli that organize their immature systems and thereby buffer them from risk for regulatory failures in sleep over a developmentally vulnerable postnatal period. [5]

Sleeping near the baby

Parents are also encouraged to sleep near their babies. 'Near' is generally understood to mean in the same room, but not in the same bed. Adult bedding often does not follow the 'no pillows, no fluffy blankets and firm mattresses only' instuctions mentioned before. Keeping the baby in the same room as the parent is thought to allow the parent to be wakened by a baby in distress even if the child is unable to cry.

Pacifiers

A 2005 study indicated that use of a pacifier is associated with a 90% reduction in the risk of SIDS (Li et al). PMID 16339767

Speculated associations

Vitamin C

Australian medical doctor Archie Kalokerinos claims to have done scientific and clinical research purporting to show that if vitamin C levels are adequate, it will prevent cot-death[6]. This has not been accepted by medical authorities[7].

Toxic gases

In 1989, a controversial piece of research by UK Scientist Barry Richardson claimed that all cot death was the result of toxic nerve gases being produced through the action of fungus in mattresses on compounds of phosphorus, arsenic and antimony. These chemicals are frequently used to make mattresses fire-retardant.

A major plank in this explanation is the widely-observed phenomenon that the risk of cot death rises from one sibling to the next. No satisfactory biological explanation for this has ever been put forward. Richardson claims that the cause is that parents are more likely to buy new bedding for their first child, and to re-use that bedding for later children. The more frequently used the bedding is, the more chance there will be that fungus has become resident in the material and thus the higher chance of cot death.

In 1994, the New Zealand government, under the advice of Dr. Jim Sprott who supports this theory, issued advice recommending new parents to either buy bedding free of the toxic compounds or to wrap the mattresses in a barrier film to prevent the escape of the gases. This has lead to a 70% drop in cot death rates in New Zealand. Dr. Sprott claims that no case of cot death has ever been traced back to a properly manufactured or wrapped mattress [8].

However, a Final Report of The Expert Group to Investigate Cot Death Theories: Toxic Gas Hypothesis, published in May 1998 concluded that "there was no evidence to substantiate the toxic gas hypothesis that antimony- and phosphorus-containing compounds used as fire retardants in PVC and other cot mattress materials are a cause of SIDS. Neither was there any evidence to believe that these chemicals could pose any other health risk to infants." (See FSID Press release)

Continual-activation Theory of SIDS

The continual-activation theory of sudden infant death syndrome proposed by Jie Zhang hypothesizes that SIDS occurs when one of two brain mechanisms that are evolved to provide a safeguard for life to go on during sleep time, failed to activate while asleep. Zhang believes that the human brain can be divided into two subsidiary systems: the conscious brain and the non-conscious brain. In order to maintain proper brain functioning, both subsidiary systems have to be continually activated through their life times. To carry out this task, Zhang suggests that there is a continual-activation mechanism in each subsidiary system of human brain. When the level of activation in a subsidiary system descends to a given threshold, the corresponding continual-activation mechanism will be triggered to generate a pulse-like activation signal. Zhang believes that both continual-activation mechanisms have to be alternately activated during sleep. According to this theory, failure of activating either continual-activation mechanism during sleep is the root cause of SIDS. (Zhang, 2005a & 2005b).

An X-linkage

There is a consistent 50% male excess in SIDS per 1000 live births of each gender. Any supposed cause of SIDS that is independent of gender (same risk for males and females) can be rejected a priori on that basis. Given a 5% male excess birth rate (105 male to 100 female live births) there appear to be 3.15 male SIDS per 2 female SIDS for a male fraction of 0.61. See http://wonder.cdc.gov and http://www3.who.int/whosis/menu.cfm?path=whosis,inds,mort&language=english for data on SIDS by gender in the U.S. and throughout the world. Mage and Donner (The fifty percent male excess of infant respiratory mortality. Acta Paediatr. 2004 Sep;93(9):1210-5; The X-linkage hypotheses for SIDS and the male excess in infant mortality. Med Hypotheses. 2004;62(4):564-7.) have shown that the 50% male excess could be caused by a dominant X-linked allele that occurs with a frequency of 1/3 that is protective of transient cerebral anoxia. An unprotected XY male would occur with a frequency of 2/3 and an unprotected XX female would occur with a frequency of 4/9. The ratio of 2/3 to 4/9 is 1.5 to 1 which matches the observed male 50% excess rate of SIDS. Although many authors have found autosomal and mitochondrial genetic risk factors for SIDS they cannot explain the male excess because such gene loci have the same frequencies for males and females. Supporting evidence is found by examination of other causes of infant respiratory death, such as inhalation of food and other foreign objects. Although food is prepared identically for male and female infants, there is a 50% male excess of death from such causes indicating that males are more susceptible to the cerebral anoxia created by such incidents in exactly the same proportion as found in SIDS. See the data found at http://wonder.cdc.gov for 9ICD 911 and 912 death rates by gender.

Reference

• Li DK, Willinger M, Petitti DB, Odouli R, Liu L, Hoffman HJ. Use of a dummy (pacifier) during sleep and risk of sudden infant death syndrome (SIDS): population based case-control study. BMJ 2005. PMID 16339767.