sudden infant death syndrome

Sudden infant death syndrome (SIDS) is marked by the sudden death of an infant that is not predicted by medical history and remains unexplained after a thorough forensic autopsy and detailed death scene investigation. As infants are at the highest risk for SIDS during sleep, it is sometimes referred to as cot death or crib death. The cause of SIDS is unknown, but some characteristics associated with the syndrome have been identified. The unique signature characteristic of SIDS is its log-normal age distribution that spares infants shortly after birth — the time of maximal risk for almost all other causes of non-trauma infant death. Other notable characteristics are its disproportionate affliction of male infants and the fact that caregivers are unaware in the preceding 24 hours that the infant is at risk of imminent sudden death. Many risk factors and medical causal relationships are proposed for SIDS. Infants sleeping prone or exposed to tobacco smoke are at greater risk than infants sleeping supine or unexposed to tobacco smoke, respectively. Genetics also play a role, as SIDS is more prevalent in males.^[1][2] SIDS prevention strategies include a well-ventilated sleeping room and putting infants on their back to sleep.^[3] Pacifiers and tummy time can help reduce known risk factors.^[4] Despite the gradual expansion of medical knowledge on SIDS causes and risk factors, definitive diagnosis remains difficult; infanticide and child abuse cases may be misdiagnosed as SIDS due to lack of evidence, and caretakers of SIDS victims are sometimes falsely accused of foul play.^[5][6] Accidental suffocations are also sometimes misdiagnosed as SIDS.^{[citation needed]}

Definition

Typically the infant is found dead after having been put to bed, and exhibits no signs of having suffered.^[7]

SIDS is a diagnosis of exclusion. It should only be applied to an infant whose death is sudden and unexpected, and which remains unexplained after the performance of an adequate postmortem investigation, including:

1. an autopsy (by an experienced pediatric pathologist, if possible);
2. investigation of the death scene and circumstances of the death;
3. exploration of the medical history of the infant and family.

Australia and New Zealand are shifting to the term "sudden unexplained death in infancy" (SUDI) for professional, scientific and coronial clarity.

The term SUDI is now often used instead of sudden infant death syndrome (SIDS) because some coroners prefer to use the term 'undetermined' for a death previously considered to be SIDS. This change is causing diagnostic shift in the mortality data.^[8]

In addition, the U.S. Centers for Disease Control and Prevention (CDC) has recently proposed that such deaths be called "sudden unexpected infant deaths" (SUID) and that SIDS is a subset of SUID.^[9]

Risk factors

The cause of SIDS is unknown. Although studies have identified risk factors for SIDS, such as putting infants to bed on their stomachs, there has been little understanding of the syndrome's biological process or its potential causes. The frequency of SIDS does appear to be influenced by the infant's sex, age and ethnicity, and the education and socioeconomic status of the infant's parents.

Listed below are several risk factors associated with increased probability of the syndrome.

Prenatal

• Maternal age — SIDS rates decrease with increasing maternal age, with teenage mothers at greatest risk.^[10]
• Delayed or inadequate prenatal care ^[10]
• Exposure to nicotine from maternal smoking — SIDS rates are higher for infants of mothers who smoke during pregnancy.^[10][11]

Postnatal

• Mold — can cause bleeding in the lungs and a variety of other uncommon conditions that may be fatal; the presence of mold correlates positively with increased incidence of SIDS. Mold-related illness is often misdiagnosed as a virus, influenza, and/or an asthma-like condition.^[12]
• Low birth weight — in the United States from 1995–98, the SIDS death rate for infants weighing 1000–1499 g was 2.89/1000; for a birth weight of 3500–3999 g, it was only 0.51/1000).^[13][14]
• Exposure to tobacco smoke^[15]
• Prone sleeping position (lying on the stomach)^[16][17]
• No breastfeeding^[18]
• Elevated or reduced room temperature^[19]
• Excesses of bedding, clothing, soft sleep surfaces, or stuffed animals^[20]
• Co-sleeping with parents or other siblings may increase risk for SIDS, but the mechanism remains unclear.^[21]
• Age of infant — SIDS incidence rises from zero at birth, is highest from two to four months of age, and declines toward zero after the infant's first year.^[22]
• Male sex — male children have a ~50% higher risk of SIDS than female children.^[23]
• Premature birth — increases risk of SIDS death roughly fourfold.^[10][13] From 1995–1998 the U.S. SIDS rate for births at 37–39 weeks of gestation was 0.73/1000; the SIDS rate for births at 28–31 weeks of gestation was 2.39/1000)^[13]
• Anemia^[24] (note, however, that per item 6 in the list of epidemiologic characteristics below, extent of anemia cannot be evaluated at autopsy because "total hemoglobin can only be measured in living infants."^[25])

Hypotheses

Bacterial infections

In a British study released May 29, 2008, researchers discovered that the common bacterial infections Staphylococcus aureus and Escherichia coli appear to be risk factors in some cases of SIDS. Both bacteria were present in greater-than-usual concentrations in infants who died from SIDS.^[26] SIDS cases peak between eight and ten weeks after birth, a time when antibodies passed from mother to child are starting to disappear, but have not yet been replenished by the infant's own antibodies.

Bed sharing

A 2005 policy statement by the American Academy of Pediatrics (AAP) on sleep environment and the risk of SIDS deemed bed sharing unsafe, recommending that infants sleep in a separate crib, bassinet, or cradle in the same room as a parent.^[27] In 2011, the AAP issued an expansion of their recommendations for a safe infant sleeping environment, in which they again recommended "room-sharing without bed-sharing", stating that such an arrangement can decrease the risk of SIDS by up to 50%. Furthermore, they recommended against devices marketed to make bed-sharing "safe", such as in-bed co-sleepers.^[28]

One trial compared 20 infants who shared their parents' bed one night and slept separately the next. The children's heart rate and oxygen saturation were monitored and analyzed together with eight hours of infrared video recording of their sleep. Although the bed-sharing infants spent some parts of the night with their airways (both mouth and nose) covered, "no consistent effect on either oxygen saturation levels or heart rate was revealed, even during prolonged bouts of airway covering." The authors concluded that "although numerous authors have suggested that bed-sharing infants face risks because of airway covering by bed-clothes or parental bodies, the present trial does not lend support to this hypothesis".^[29]

Brain disorders

According to a 2006 study in the Journal of the American Medical Association (JAMA), some babies who die of SIDS have abnormalities in the brain stem (medulla oblongata) of underdeveloped serotonin receptors (which help control functions like breathing, blood pressure and arousal) and abnormalities in serotonin signaling. According to the National Institutes of Health, this finding was the strongest evidence at that time that structural differences in a specific part of the brain may contribute to the risk of SIDS.^[30] This abnormality can continue postpartum until the end of the baby's first year, possibly accounting for the increased SIDS risk in premature infants and declining risk in children over 12 months of age. The authors noted that males have fewer serotonin receptors than females, perhaps contributing to the greater frequency of SIDS in males, but their follow-up 2010 paper failed to reconfirm that gender difference.^[31]

Another 2006 study showed that a possible cause of SIDS parents leaving their infants in an angled (feet up, head down) position known as the Trendelenburg position.^[32] This position can cause the brain stem to fall; in severe cases, the brain becomes "crushed". Recommended positions for resting infants include Fowler's position and Sims' position.^{[citation needed]}

A 2010 study suggests Interleukin-2, a neuromodulator, as the potential mechanism of SIDS. Intense neuronal IL-2 immunoreactivity in brainstems of SIDS victims was found, which could be responsible for decreased cardiorespiratory and arousal responses.^[33]

Central respiratory pattern deficiency

Ongoing research in the pediatric/neonatal community has begun to associate apnea-like breathing cessations in animal models with unusual neural architecture or signal transduction in central pattern generator circuits, including the pre-Bötzinger complex.^[34]

Cervical spinal injury from birth trauma

During birth, if the infant's head is traumatically turned side to side, upper cervical spinal injury can result. Difficulty breathing is a classic sign of upper spinal cord and brainstem injury.^[35] When infants with undiagnosed upper cervical spinal cord injury are continually placed on their stomachs for sleep, they are forced to turn their heads to the side to breathe.

Child abuse

Several instances of infanticide have been uncovered where the diagnosis was originally SIDS.^[5][6] This has led some researchers to estimate that 5% to 20% of SIDS deaths are actually infanticides.^{[36][37][38][39]} In 1997 The New York Times, covering the book The Death of Innocents: A True Story of Murder, Medicine and High-Stakes Science, wrote:

The misdiagnosis of infanticide as SIDS "happens all over," Ms. Talan, a medical reporter at Newsday, said. "A lot of doctors and police don't know how to handle it. They don't take it as seriously as they should." As a result of the book's revelations, people are starting to scrutinize possible cases of this "perfect crime," which involves no physical evidence and no witnesses.^[40]

A United Kingdom pediatrician, Roy Meadow believes that many cases diagnosed as SIDS are really the result of child abuse on the part of a parent. During the 1990s and early 2000s, a number of mothers of multiple apparent SIDS victims were convicted of homicide to various extents, on the basis of Meadow's opinion. In 2003 a number of high-profile acquittals brought Meadow's theories into disrepute. Several hundred murder convictions were reviewed, leading to several high-profile cases being reopened and convictions overturned. Meadow's medical license was revoked in 2005,^[41] after which he appealed to the High Court, which ruled in his favour in February 2006. The General Medical Council appealed to the Court of Appeal and in October 2006 by a majority decision, with the Master of the Rolls, Sir Anthony Clarke, dissenting, the Court of Appeal upheld the decision of the High Court in part, ruling that Meadow's misconduct was not sufficiently serious to merit the punishment which he had received.

The Royal Statistical Society issued a media release refuting the expert testimony in one UK case in which the conviction was subsequently overturned.^[42]

Genetics

There is a consistent 50% male excess in SIDS per 1000 live births of each sex. Given a 5% male excess birth rate (105 male to 100 female live births) there appear to be 3.15 male SIDS cases per 2 female, for a male fraction of 0.61.^[1][2] This value of 61% in the US is an average of 57% black male SIDS, 62.2% white male SIDS and 59.4% for all other races combined. Note that when multiracial parentage is involved, infant "race" is arbitrarily assigned to one category or the other; most often it is chosen by the mother. The X-linkage hypothesis for SIDS and the male excess in infant mortality have shown that the 50% male excess could be related to a dominant X-linked allele, occurring 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 researchers 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 for an X-linkage is found by examining other causes of infant respiratory death, such as suffocation by inhalation of food or other foreign objects. Although food is prepared identically for male and female infants, there is a similar 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.^{[43][original research?]}

The 2006 JAMA study which indicated a relationship between fewer serotonin binding sites and SIDS noted that the boys "had significantly fewer serotonin binding sites than girls",^[30] but the authors could not reproduce that result in their 2010 paper.^[31] This neurological imbalance decreases with age, but the increased male SIDS risk of approximately 61% persists throughout each month in the first year of life.^[44] Furthermore, this cannot explain the identical male overrepresentation in other respiratory mortality causes, such as respiratory distress syndrome or suffocation from inhalation of food or foreign objects cited above, that also exists for ages of 1–14 years in the U.S. from 1979 to 2005.^{[13][original research?]}

Inner ear damage

Records of hearing tests (oto-acoustic emissions/OAEs) administered to certain infants show that those who later died of SIDS had differences in the pattern of these tests compared with normal babies. The OAE signal-to-noise ratio was reduced in the right ears of SIDS babies (Rubens DD et al. Early Human Development 84, 225-9 (2008)).^[45] It should be noted this was a small study (n=31 cases and 31 controls) with serious limitations (several significant factors were not controlled), and has been criticised from various perspectives.^[46] The authors' suggestion for the cause of SIDS is that the deaths are caused by disturbances in respiratory control other than suffocation. The vestibular apparatus of the inner ear has been shown to play an important role in respiratory control during sleep; this inner ear damage could be linked to SIDS. The authors speculate that the damage occurs during delivery, particularly when prolonged contractions create greater blood pressure in the placenta. The right ear is directly in the "line of fire" for blood entering the fetus from the placenta, and thus could be more susceptible to damage. If the findings are relevant, it may be possible to take corrective measures. Researchers are beginning animal studies to explore the connection.^[47]

Nitrogen dioxide

A 2005 study by researchers at the University of California, San Diego found that "SIDS may be related to high levels of acute outdoor NO₂ exposure during the last day of life."^[48] While nitrogen dioxide (NO₂) exposure may be one of many possible risk factors, it is not considered causal, and the report cautioned that further studies were needed to replicate the result.

Toxic gases

In 1989, a controversial piece of research by UK scientist Barry Richardson claimed that all cot deaths were 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.^{[citation needed]}

Support for this hypothesis was based on the observation that the risk of cot death rises from one sibling to the next.^{[citation needed]} Richardson claimed that parents are more likely to buy new bedding for their first child, and to reuse that bedding for later children. The more frequently used the bedding, the more chance that fungus has become resident in the material; thus, a higher chance of cot death. A paper by Peter Fleming and Peter Blair^[49] references evidence from other studies that both supports and refutes the increasing occurrence of SIDS with mattress sharing, suggesting that this is still inconclusive.

Dr. Jim Sprott recommends new parents either buy bedding free of the toxic compounds or wrap the mattresses in a barrier film to prevent escape of the gases. Sprott claims that no case of cot death has ever been traced to a properly manufactured or wrapped mattress.^[50]

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."^[51] The report also states that "in normal cot-like conditions it is not possible to generate toxic gas from antimony in mattresses" and that "babies have also been found to die on wrapped mattresses."

According to Dr. Sprott, as of 2006, the New Zealand government has not reported any SIDS deaths when babies have slept on mattresses wrapped according to his method. While the Limerick report claims that babies have been found to die on wrapped mattresses, Dr. Sprott argues that a chemical analysis of the bedding should be performed. He additionally claims that this part of the report was flawed:

In February 2000 Dr. Peter Fleming (a co-author of the Limerick Report and principal author of the UK CESDI Report) conceded that the claim that three babies in the United Kingdom had died of cot death on polythene-covered mattresses could not be substantiated.^[52]

Vaccination

Vaccination does not increase the risk of SIDS, and may reduce the risk slightly.^[53][54]

According to the US Centers for Disease Control and Prevention:

From 2 to 4 months old, babies begin their primary course of routine vaccinations. This is also the peak age for sudden infant death syndrome (SIDS). The timing of these two events has led some people to believe they might be related. However, studies have concluded that vaccines are not a risk factor for SIDS.^[54]

Vitamin C

In the 1970s, high doses of vitamin C were touted as a preventive measure for SIDS,^[55] although the claim was controversial even then.^[56][57] Subsequent studies failed to support a preventive role for vitamin C in SIDS.^[58] To the contrary, a 2009 study found that high levels of vitamin C were strongly associated with SIDS, possibly through a pro-oxidant interaction with iron.^[59]

Differential diagnosis

Some conditions that are often undiagnosed and could confused with or comorbid with SIDS include:

• medium-chain acyl-coenzyme A dehydrogenase deficiency (MCAD deficiency)^[60]
• infant botulism^[61]
• long QT syndrome (accounting for less than 2% of cases)^[62]
• Helicobacter pylori bacterial infections^[63]
• shaken baby syndrome and other forms of child abuse^[64][65]
• overlying^[66]

For example, an infant with MCAD deficiency could have died by "classical SIDS" if found swaddled and prone with head covered in an overheated room where parents were smoking. Genes indicating susceptibility to MCAD and Long QT syndrome do not protect an infant from dying of classical SIDS. Therefore, presence of a susceptibility gene, such as for MCAD, means the infant may have died either from SIDS or from MCAD deficiency. It is currently impossible for the pathologist to distinguish between them.

A 2010 study looked at 554 autopsies of infants in North Carolina that listed SIDS as the cause of death, and suggested that many of these deaths may have been due to accidental suffocation. The study found that 69% of autopsies listed other possible risk factors that could have led to death, such us unsafe bedding or sleeping with adults.^[67]

Prevention

Air circulation with fan use

According to a study of nearly 500 babies published in the October 2008 Archives of Pediatrics & Adolescent Medicine, using a fan to circulate air correlates with a lower risk of sudden infant death syndrome. This is plausible because a prone sleeping baby with nose to the sleeping surface could rebreathe some of its exhaled breath which is enriched in CO2 and depleted in oxygen. A fan could increase the mixing of the exhalation into the room air and lessen the risk of SIDS related to infant hypoxia. Researchers took into account other risk factors and found that fan use was associated with a 72% lower risk of SIDS. Only 3% of the babies who died had a fan on in the room during their last sleep, the mothers reported. That compared to 12% of the babies who lived. Using a fan reduced risk most for babies in poor sleeping environments.^[3] Author De-Kun li said that "the baby's sleeping environment really matters" and that "this seems to suggest that by improving room ventilation we can further reduce risk."^[68]

However, Dr. John Olssen at East Carolina University has pointed out that this study had a number of methodological flaws, such as selection and recall bias, low enrollment numbers, and dissimilar study groups. Olssen argues that although fan use is probably not harmful, it should not be recommended as a means to reduce the risk of SIDS.^[69]

Bedding

Product safety experts advise against using pillows, sleep positioners, bumper pads, stuffed animals, or fluffy bedding in the crib and recommend instead dressing the child warmly and keeping the crib "naked."^[70][71]

Blankets should not be placed over an infant's head.^[72] It has been recommended that infants should be covered only up to their chest with their arms exposed. This reduces the chance of the infant shifting the blanket over his or her head.

Breastfeeding

A 2003 study published in Pediatrics, which investigated racial disparities in infant mortality in Chicago, found that previously or currently breastfeeding infants in the study had 1/5 the rate of SIDS compared with non-breastfed infants, but that "it became nonsignificant in the multivariate model that included the other environmental factors". These results are consistent with most published reports and suggest that other factors associated with breastfeeding, rather than breastfeeding itself, are protective."^[73] A single more recent study claims to show a significantly reduced incidence of SIDS in breastfed infants.^[74]

Bumper pads

Bumper pads may be a contributing factor, claims Health Canada, the Canadian government's health department. They issued an advisory^[75] recommending against the use of bumper pads, stating:

The presence of bumper pads in a crib may also be a contributing factor for Sudden Infant Death Syndrome (SIDS). These products may reduce the flow of oxygen rich air to the infant in the crib. Furthermore, proposed theories indicate that the re-breathing of carbon dioxide plays a role in the occurrence of SIDS.

Concerns regarding recommendations

Dr. Rafael Pelayo from Stanford University and a number of other pediatric sleep researchers in the US have stated that they believe that the American Academy of Pediatrics' recommendations regarding cosleeping and pacifier use may have unintended consequences. They have stated that the SIDS prevention strategy of the American Academy of Pediatrics which keeps infants at a low arousal threshold and reduces the time in quiet sleep may be unhealthy for children. They state that slow wave sleep is the most restorative form of sleep and limiting this sleep in the first 12 months of life may have unintended consequences to both the sleep and the infant.^[76]

According to a 1998 study by British researchers that compared back sleeping infants to stomach sleeping infants there were developmental differences at 6 months of age between the two groups. At 6 months of age the stomach sleeping infants had higher gross motor scores, social skills scores, and total development skills scores than the back sleeping infants. The differences were apparent at the 5% statistical significant level. But, at 18 months the differences were no longer apparent. The researchers deemed the lower development scores of back sleeping infants at 6 months of age to be transient and stated that they do not believe the back sleeping recommendations should be changed.^[77] Other scientists have stated that the conclusion that the negative effects of back sleep at 18 months of age is transient is based upon very little evidence and that no long-term randomized trials have been completed.^[78]

Other side effects of the back sleeping position include increased rates of shoulder retraction, positional plagiocephaly, and positional torticollis.^[79] Some scientists dispute that plagiocephaly is a negative side effect. Dr. Peter Fleming, who is co-author of the study that deemed delays at 6 months of age to be transient, has stated that he does not think plagiocephaly is a negative side effect of back sleep. In an interview with the Guardian Dr. Fleming stated "I do not think it is a medical problem—it is more of a cosmetic one. Mothers may feel it is a syndrome and a problem when it really is nonsense."^[80] A research study on children with plagiocephaly plus a confounding condition such as premature birth or failure to thrive, found that 26% had mild to severe psychomotor delay. This study also showed that 10% of infants with plagiocephaly had mild to severe mental development delay.^[81]

Because of the delays caused by back sleep some medical professionals have suggested that the "normal" ages at which children had previously attained developmental milestones should be pushed back. This would enable medical professionals to consider "normal" children who previously were considered developmentally delayed.^[82]

Additional studies have reported that the following negative conditions are associated with the back sleep position: increase in sleep apnea, decrease in sleep duration, strabismus, social skills delays, deformational plagiocephaly, and temporomandibular jaw difficulties.^[79] In addition, the following are symptoms that are associated with sleep apnea: growth abnormalities, failure to thrive syndrome in infants, neurocognitive abnormalities, daytime sleepiness, emotional problems, decrease in memory, decrease in learning, and a delay in nonverbal skills. The conditions associated with deformational plagiocephaly include visual impairments, cerebral dysfunction, delays in psychomotor development and decreases in mental functioning. The conditions associated with gross motor milestone delays include speech and language disorders. In addition, it has been hypothesized that delays in motor skills can have a negative impact on the development of social skills.^[83][84] In addition, other studies have reported that the prone position prevents subluxation of the hips, increases psychomotor development, prevents scoliosis, lessens the risk of gastroesophageal reflux, decreases infant screaming periods, causes less fatigue in infants, and increases the relief of infant colic.^[85] In addition, prior to the "Back to Sleep" campaign many babies self-treated their own torticollis by turning their heads from one side to the other while sleeping in the prone position.^[86] Supine sleeping infants cannot self-treat their own torticollis.

Pacifiers

According to a 2005 meta-analysis, most studies favor pacifier use.^[4] According to the American Academy of Pediatrics, pacifier use seems to reduce the risk of SIDS, although the mechanism by which this happens is unclear.^[87] SIDS experts and policy makers haven't recommended the use of pacifiers to reduce the risk of SIDS because of several problems associated with pacifier use, like increased risk of otitis, gastrointestinal infections and oral colonization with Candida species.^[87] A 2005 study indicated that use of a pacifier is associated with up to a 90% reduction in the risk of SIDS depending on the ambient factors, and it reduced the effect of other risk factors.^[88] It has been speculated that the raised surface of the pacifier holds the infant's face away from the mattress, reducing the risk of suffocation. If a postmortem investigation does not occur or is insufficient, a suffocated baby may be misdiagnosed with SIDS.

A 2010 study at Monash University suggests pacifiers can prevent SIDS by changing sleep patterns. They believe a pacifier ensures the baby remains in a light sleep and is more easily aroused if they feel uncomfortable.^[89] The most recent 2011 study confirms that pacifier usage also reduces SIDS risks from other known SIDS risk factors^[90]

Secondhand smoke reduction

According to the US Surgeon General's Report, secondhand smoke is connected to SIDS.^[91] Infants who die from SIDS tend to have higher concentrations of nicotine and cotinine (a biological marker for secondhand smoke exposure) in their body fluids than those who die from other causes.^[92] Parents who smoke can significantly reduce their children's risk of SIDS by either quitting or smoking only outside and leaving their house completely smoke-free.

The maternal pregnancy smoking rate decreased by 38% between 1990 and 2002.^[93]

Sleep positioning

A plot of SIDS rate from 1988 to 2006

Sleeping on the back has been recommended by (among others) the American Academy of Pediatrics (starting in 1992) to avoid SIDS, with the catchphrases "Back To Bed" and "Back to Sleep". The incidence of SIDS has fallen sharply in a number of countries in which the back to bed recommendation has been widely adopted, such as the US and New Zealand.^[94]

Among the theories supporting the Back to Sleep recommendation is the idea that small infants with little or no control of their heads may, while face down, inhale their exhaled breath (high in carbon dioxide) or smother themselves on their bedding—the brain-stem anomaly research (above) suggests that babies with that particular genetic makeup do not react "normally" by moving away from the pooled CO₂, and thus smother. Another theory^[95] is that babies sleep more soundly when placed on their stomachs, and are unable to rouse themselves when they have an incidence of sleep apnea, which is thought to be common in infants.

Hospital neonatal-intensive-care-unit (NICU) staff commonly place preterm newborns on their stomach, although they advise parents to place their infants on their backs after going home from the hospital.^[96]

Sleep sacks

In colder environments where bedding is required to maintain a baby's body temperature, the use of a "baby sleep bag" or "sleep sack" is becoming more popular. This is a soft bag with holes for the baby's arms and head. A zipper allows the bag to be closed around the baby. A study published in the European Journal of Pediatrics in August 1998^[97] 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 its 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." The American Academy of Pediatrics also recommends them as a type of bedding that warms the baby without covering its head.^[98]

Epidemiology

SIDS was responsible for 0.543 deaths per 1,000 live births in the US in 2005.^[13] It is responsible for far fewer deaths than congenital disorders and disorders related to short gestation, though it is the leading cause of death in healthy infants after one month of age.

SIDS deaths in the US decreased from 4,895 in 1992 to 2,247 in 2004.^[99] But, during a similar time period, 1989 to 2004, SIDS being listed as the cause of death for sudden infant death (SID) decreased from 80% to 55%.^[99] According to Dr. John Kattwinkel, chairman of the Centers for Disease Control and Prevention (CDC) Special Task Force on SIDS "A lot of us are concerned that the rate (of SIDS) isn't decreasing significantly, but that a lot of it is just code shifting".^[99]

A set of 14 epidemiologic characteristics associated with SIDS have been identified:^[100][101]

1. A characteristic 4-parameter lognormal age distribution;
2. Increased risk associated with prone sleep position;
3. Prone and supine SIDS have same age and gender distributions;
4. Male and female SIDS have same age distribution;
5. Total sudden respiratory deaths at home have same age and gender distributions;^[102]
6. No evidence of cause of death at forensic autopsy and death scene investigation;
7. SIDS spares infants at birth[?];
8. Seasonality: winter maximum, summer minimum;
9. Increasing SIDS rate with Live Birth Order;
10. Consistent male excess of approximately 50%;
11. Low increased risk of SIDS in subsequent siblings of SIDS;
12. Parental smoking is a risk factor for SIDS;
13. Apparent Life Threatening Events (ALTE) are not a risk factor for subsequent SIDS;
14. SIDS risk is greatest during sleep.

References

Further reading

• Ottaviani, G. (2007). Crib death. Sudden unexplained death of infants: the pathologist's viewpoint. Berlin Heidelberg, Germany: Springer. ISBN 978-3-540-49370-9. 
• Joan Hodgman; Toke Hoppenbrouwers (2004). SIDS. Calabasas, Calif: Monte Nido Press. ISBN 0-9742663-0-2. 
• Lewak N. "Book Review: SIDS". Arch Pediatr Adolesc Med 158 (4): 405. http://archpedi.highwire.org/cgi/content/full/158/4/405. 

See also

• Women and smoking: Unique gender differences and health effects for Females

External links

• SIDS at the Open Directory Project