sudden infant death syndrome

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sudden infant death syndrome

sudden infant death syndrome (SIDS) or crib death, sudden, unexpected, and unexplained death of an apparently healthy infant under one year of age (usually between two weeks and eight months old). SIDS accounts for 10% of infant deaths and is the second highest cause of death (after accidents) in infancy. The risk is higher in males, in low-birth-weight infants, in lower socioeconomic levels, during cold months, and for babies who sleep face down.

Causal theories suggest that the infant may have immature or hypersensitive lungs, may have a defect in brain-stem control of breathing, or may be rebreathing carbon dioxide. Recent studies have shown persistent high levels of an infant form of hemoglobin in babies with known risk factors for the condition.

SIDS victims are thought to have brief episodes of apnea (breathing stoppage) before the fatal one. An alarm system that detects breathing abnormalities is sometimes used with infants suspected of being prone to SIDS. The American Academy of Pediatrics has recommended that babies be laid to sleep on their backs or sides.

The Columbia Electronic Encyclopedia Copyright © 2004.
Licensed from Columbia University Press

sudden infant death syndrome (SIDS)

or crib death

Unexpected death of an apparently well infant. It occurs almost always during sleep at night and usually at 2–4 months of age. Sleeping facedown and exposure to cigarette smoke have been implicated. It is more common in cases of premature birth, low birth weight, and poor prenatal care. Many cases that would once have been labeled SIDS prove to be due to suffocation in bedding or overheating. Some babies who die of SIDS have been found to have brain stem abnormalities that interfere with their response to high levels of carbon dioxide in the blood.

Learn more about sudden infant death syndrome (SIDS) with a free trial on Britannica.com.

Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.

Sudden infant death syndrome

Sudden infant death syndrome (SIDS) is a syndrome marked by the symptoms of sudden and unexplained death of an apparently healthy infant aged one month to one year. The term cot death is often used in the United Kingdom, Australia and New Zealand, while crib death is sometimes used in North America.

Overview

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

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

an autopsy;
investigation of the scene and circumstances of the death;
exploration of the medical history of the infant and family.

SIDS is responsible for roughly 1 death per 2,000 births in the U.S. 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 babies after one month of age.

SIDS deaths in the U.S. decreased from 4,895 in 1992 to 2,247 in 2004 . 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% . According to Dr. John Kattwinkel, chairman of the Center for Disease Control (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” .

SIDS Back To Sleep Campaign: History and Theory

In 1992, based upon epidemiological evidence and studies of sleep physiology, the American Academy of Pediatrics began advising parents to place their newborn infants to sleep on their backs (supine position) instead of their stomachs (prone position). This advice is based on the physiological evidence which shows that infants who sleep on their back have lower arousal thresholds and less Slow-Wave Sleep (SWS) compared to infants that sleep on their stomachs. . In human infants sleep develops rapidly during early development. This development includes an increase in non-rapid eye movement sleep (NREM sleep) which is also called Quiet Sleep (QS) during the first 12 months of life in association with a decrease in rapid eye movement sleep (REM sleep) which is also known as Active Sleep (AS) . In addition, slow wave sleep (SWS) which consists of Stage 3 and Stage 4 NREM sleep appears at 2 months of age . and it is theorized that some infants have a brain-stem defect which increases their risk of being unable to arouse from SWS (also called Deep Sleep) and therefore have an increased risk of SIDS due to their increased inability to arouse from SWS . In a currently utilized model that explains the process in which slow wave sleep is involved in memory consolidation the hippocampus acts as a temporary storage facility for new memories which are then transferred to the neocortex during slow wave sleep (SWS) .

A significant way of decreasing slow wave sleep in infants is by changing their sleeping position from their stomach to their back. It has been shown in studies of preterm infants full-term infants , and older infants . , that they have greater time periods of quiet sleep and also decreased time awake when they are positioned to sleep on their stomachs. In both human infants and rats, arousal thresholds have been shown to be at higher levels in the Electroencephalography (EEG) during Slow-wave sleep .

In 1992 , a SIDS risk reduction strategy based upon lowering arousal thresholds during SWS was implemented by the American Academy of Pediatrics (AAP) which began recommending that healthy infants be positioned to sleep on their back (supine position) or side (lateral position), instead of their stomach (prone position), when being placed down for sleep. The AAP’s 1992 recommendations were announced five years after the Netherlands had started it’s infant supine sleep position campaign in 1987 . The Netherlands recommendations were followed by infant supine sleep position campaigns in the United Kingdom, New Zealand, and Australia in 1991, the U.S. and Sweden in 1992, and Canada in 1993 . In 1994 , a number of organizations in the United States combined to further communicate these non-prone sleep position recommendations and this became formally known as the “Back To Sleep” campaign. In 1996 , the AAP further refined its sleep position recommendation by stating that infants should only be placed to sleep in the supine position and not in the prone or lateral positions.

In 1992, the first National Infant Sleep Position (NISP) Household Survey was conducted to determine the usual position in which U.S. mothers placed their babies to sleep: (1) Lateral (side); (2) Prone (stomach); (3) Supine (back); (4) Other; (5) No Usual Position. According to the 1992 NISP survey, 13.0% of U.S. infants were positioned in the supine position for sleep . According to the 2006 NISP survey 75.7% of infants were positioned in the supine position to sleep .

Since 1998 there have been several studies published which report that infants placed to sleep in the supine position lag in motor skills, social skills, and cognitive ability development when compared to infants who sleep in the prone position. In the 1998 article entitled “Effects of Sleep Position on Infant Motor Development.” [14] by Davis, Moon, Sachs, and Ottolini, the authors state “We found that sleep position significantly impacts early motor development.” The prone (stomach) sleeping infants in this study slept an average of 225.2 hours (8.3%) more in their first 6 months of life than the supine (back) sleeping infants.

In the 1998 article entitled “Does the Supine Sleeping Position Have Any Adverse Effects on the Child? II. Development in the First 18 Months” by Dewey, Fleming, Golding, and the ALSPAC Study Team the objective of the study was “To assess whether the recommendations that infants sleep supine could have adverse consequences on their motor and mental development.” They utilized the Denver Developmental Screening Test (DDST) and studied infants at 6 and 18 months. According to the study, at 6 months of age, the infants who were placed to sleep in the prone position had statistically significant higher social skills scores, gross motor scores, and total development scores than those infants who were put to sleep in the supine position. In addition, the total development scores of prone sleeping infants were still higher than supine sleeping infants at 18 months of age but were no longer statistically significant. In the 2005 article entitled “Influence of supine sleep positioning on early motor milestone acquisition” by Majnemer and Barr they utilized the Alberta Infant Motor Scale Scores (AIMS Scores) to analyze the impact of infant sleep position. They reported that “Typically developing infants who were sleep-positioned in supine had delayed motor development by age 6 months, and this was significantly associated with limited exposure to awake prone positioning.” But, the authors also note that awake prone (stomach) positioning is associated with prone (stomach) sleeping. No studies have been conducted which compare supine sleeping infants who have regular awake prone positioning (tummy time) to prone sleeping infants who have regular awake prone positioning (tummy time).

Placing infants on their stomachs while they are awake (tummy time) has been recommended to offset the motor skills delays associated with the back sleep position but positioning the infant on their stomach while awake will not impact the amount of slow wave sleep [39-43] since tummy time only occurs when an infant is awake.

Undiagnosed conditions

Some conditions that may be undiagnosed and thus result in a diagnosis of SIDS include

medium-chain acyl-coenzyme A dehydrogenase deficiency (MCAD deficiency);
infant botulism;
long QT syndrome;
infections with the bacterium Helicobacter pylori;
shaken baby syndrome and other forms of child abuse.

Risk factors

Very little is certain about the possible causes of SIDS, and there is no proven method for prevention. 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 cause or causes. The frequency of SIDS appears to be a strong function of infant sex and the age, ethnicity, and the education and socio-economic status of the parents.

According to a study published in October 2007 in the Journal of the American Medical Association, babies who die of SIDS have abnormalities in the part of the brain called the medulla oblongata which helps control functions like breathing, blood pressure and arousal. Researchers examined the brains of 31 babies who had died of SIDS and 10 who had died from other causes. It was discovered that the medulla oblongata had neurons that released a chemical called serotonin. The number of these neurons was greater than normal in 55% of the brains of the babies who had died of SIDS. They also found that babies had fewer receptors for serotonin and that abnormalities in the brain stem appear to affect the ability to use and recycle serotonin, which is responsible for regulating mood as well as vital body functions. According to the National Institutes of Health, which funded the study, the new finding is the strongest evidence to date suggesting that innate differences in a specific part of the brain may place some at increased risk of dying from SIDS.

In a British study released May 29 2008 researchers discovered that the common bacterial infections Staphylococcus aureus (staph) and Escherichia coli (E. coli) appear to be the cause of some cases of Sudden Infant Death Syndrome. Both the "staph" and E. coli bacteria had a greater presence in the unexplained deaths of infants. SIDS cases peak between eight and ten weeks after birth, which is also the time frame in which the antibodies that were passed along from mother to child are starting to disappear and babies have not yet made their own antibodies.

Listed below are several factors associated with increased probability of the syndrome based on information available prior to this recent study.

Prenatal risks

maternal nicotine use (tobacco or nicotine patch)
inadequate prenatal care
inadequate prenatal nutrition
use of heroin
subsequent births less than one year apart
alcohol use
being overweight
Teen pregnancy (the more babies a teen mother has, the greater the risk)
infant's sex (61% of SIDS cases occur in males)

Post-natal risks

low birth weight (especially less than 1.5 kg (~3.3 lb))
exposure to tobacco smoke
prone sleep position (lying on the stomach, see sleep positioning below)
not breastfeeding
elevated room temperature
excess bedding, clothing, soft sleep surface and stuffed animals
infant's age (incidence rises from zero at birth, is highest from two to four months, and declines towards zero at one year)
premature birth (increases risk of SIDS death by 50 times)

Risk reduction for SIDS

Though SIDS cannot be prevented, parents of infants are encouraged to take several precautions in order to reduce the likelihood of SIDS.

Environment

Sleep positioning

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. However, the absolute incidence of SIDS prior to the Back to Sleep Campaign was already low in the US.

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 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.

Arguments against infant back-sleeping include concerns that an infant could choke on fluids it brings up. Hospital staff commonly place newborns on their side, although they advise parents to place their infants on their backs after going home from the hospital.

Other concerns raised about the Back to Sleep Campaign have included the possible increase the risk of positional facial and head deformities (see positional plagiocephaly), possible interference with development of good sleep habits (which in turn may have other bad effects), and possible interference with motor skills development (as infants delay attempts to lift their heads, crawl, etc.).

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 as 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.

Co-sleeping

A controversial approach to lowering SIDS rates is limiting co-sleeping. 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.

However, some data has suggested that almost all SIDS deaths in adult beds occur when other prevention methods, such as placing infants on their backs, are not used. Co-sleeping studied in the West has been present mostly in poorer families where other risk factors are present,. while co-sleeping in other cultures such as in China is more prevalent and is done in combination with practices such as sleeping children on their back, correlating with a significantly lower rate of SIDS than the West.. There are also evolutionary theories as to why co-sleeping would be healthier for infants than sleeping alone. Further studies have suggested that factors associated with safe co-sleeping such as enhanced infant arousals are responsible for a positive contribution to SIDS prevention.

Secondhand smoke reduction

According to the U.S. Surgeon General’s Report, secondhand smoke is connected to SIDS. Infants who die from SIDS tend to have higher concentrations of nicotine and cotinine (a biological marker for secondhand smoke exposure) in their lungs than those who die from other causes. Infants exposed to secondhand smoke after birth are also at a greater risk of SIDS. 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 1990-2002 .

Sleeping area

Bedding

To prevent SIDS, many families use firm mattresses with tight-fitting sheets in cribs or bassinets. The families do not allow pillows, stuffed animals, or fluffy bedding in the cribs. In cold weather, the families dress the infants warmly in well-fitted clothing..''

Infants' blankets should also not be placed over their heads. It has been recommended that the infants are only covered up to their chest with their arms exposed. This will help eliminate the chances of the infant moving the blanket over their head.

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 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."

Pacifiers

A 2005 study indicated that use of a pacifier is associated with a 90% reduction in the risk of SIDS. 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. Although suffocation is an actual cause, while SIDS refers to an unexplained infant death, in the absence of sufficient postmortem investigation, a SIDS diagnosis may result.

Air circulation with fan use

According to a study of nearly 500 babies published the October 2008 Archives of Pediatrics & Adolescent Medicine, using a fan to circulate air correlates with a lower risk of sudden infant death syndrome. Researchers took into account other risk factors and found that fan use was associated with a 72 percent lower risk of SIDS. Only 3 percent of the babies who died had a fan on in the room during their last sleep, the mothers reported. That compared to 12 percent of the babies who lived. Using a fan reduced risk most for babies in poor sleeping environments.

Bumper pads

Bumper pads may be a contributing factor in SIDS deaths and should be removed. Health Canada, the Canadian government's health department, issued an advisory 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 rebreathing of carbon dioxide plays a role in the occurrence of SIDS.

Speculated associations

A number of theoretical causes have been proposed as a trigger for SIDS, but many of them are unproven or have not been thoroughly studied and peer-reviewed.

Mattress bugs

A 2002 study hypothesized that bugs feeding on baby vomit and dust could be fatal for small children, creating 'supertoxins' which spur the baby's body into overreacting, leading to anaphylactic shock.

Brain disorder

A recently published research article in the Journal of the American Medical Association showed evidence that cells in the brainstem fail to develop receptors for Serotonin in the womb. This abnormality continues until after birth, supposedly until the end of their first year. This would account for there being few to no SIDS deaths after the first year of infancy and the reason the risk is more for premature infants. The SIDS Alliance/First Candle has posted a message about this along with a link to the abstract on their website (www.firstcandle.com), which can be accessed from the front page

Vitamin C

According to a 1993 article in Journal of Orthomolecular Medicine, Australian medical doctor Archie Kalokerinos performed research showing that high doses of vitamin C eliminates SIDS. As SIDS was shown to be caused solely by vitamin deficiency, the article stated that it was no longer a syndrome, and that the proper disease name is now SID. As of January 2007, the Journal of Orthomolecular Medicine was not included among journals selected by the U.S. National Library of Medicine for inclusion in their Medline database.

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.

A major plank in this explanation is the widely-observed phenomenon that the risk of cot death rises from one sibling to the next. 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; thus, a higher chance of cot death. A paper by Peter Fleming and Peter Blair references evidence from other studies that both supports and refutes the increasing occurrence of SIDS with mattress sharing and suggests that this is still inconclusive.

In 1994, the New Zealand government, under the advice of Dr. Jim Sprott, 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. Dr. Sprott claims that no case of cot death has ever been traced back to a properly manufactured or wrapped mattress

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. The report also states that "in normal cot-like conditions it is not possible to generate toxic gas from antimony in mattresses" and "babies have also been found to die on wrapped mattresses." Dr. Sprott's website, however, claims that the study does not actually refute his theory:

Contrary to media publicity, the 1998 UK Limerick Report did not disprove the toxic gas theory—as a highly qualified environmental scientist has stated in the New Zealand Medical Journal. In fact, the Limerick Committee's experiments proved the fungal generation of toxic gases (forms of stibine and arsine) from cot mattress materials.

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.

Central Respiratory Pattern Deficiency

There is ongoing research in the pediatric/neonatal community that 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. It is possible that irregularities in neurotransmitter release (such as GABA, adenosine, and NMDA) or deficiencies in their associated receptors (including both GABA_A, GABA_B subtypes and NMDA-glutamate receptors) are linked to incomplete prenatal development as is evident in pre-term infants.

Genetic factors are also being studied with several rat and mouse knockouts.

Upper cervical spinal cord injury as a result of 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 brain-stem injury. When infants with undiagnosed upper cervical spinal cord injury are continually placed on their stomach for sleep, they are forced to turn their head to the side to breathe. This is hypothesised to aggravate and prolong the spinal cord injury sustained during birth, preventing proper healing and ultimately leading to fatal breathing difficulty.

Gender

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 per 2 female SIDS for a male fraction of 0.61. The X-linkage hypotheses for SIDS and the male excess in infant mortality have shown that the 50% male excess could be caused by a dominant X-linked allele that occurs with a frequency of ⅓ that is protective of transient cerebral anoxia. An unprotected XY male would occur with a frequency of ⅔ and an unprotected XX female would occur with a frequency of . The ratio of ⅔ to 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 sex.

The study which indicated that there was a relationship between fewer serotonin binding sites and SIDS noted that the boys "had significantly fewer serotonin binding sites than girls".

Child abuse

Several instances of infanticide have been uncovered where the diagnosis was originally SIDS. This has led some researchers to estimate that 5% to 20% of SIDS deaths are infanticides. In 1997 The New York Times, covering a book called 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.

British former pediatrician 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 number of mothers of multiple apparent SIDS victims were convicted of murder, to varying degrees 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 re-opened and convictions overturned.

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

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. 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.

Vaccination

According to the CDC's page on SIDS and vaccines:

Inner ear damage

Records of hearing tests administered to certain infants show that those who later died of SIDS had a unique pattern of partial hearing loss, according to the journal Early Human Development. One suggestion for the cause of SIDS is that the deaths are caused by disturbances in respiratory control (from other than suffocation). The vestibular apparatus of the inner ear has been shown to play an important role in respiratory control during sleep. It is speculated that this inner ear damage could be linked to SIDS. It is speculated 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 most 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.

Side effects of SIDS risk reduction recommendations

Dr. Rafael Pelayo from Stanford University and a number of other pediatric sleep researchers in the U.S. 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.

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. 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.

Other side effects of the back sleeping position include increased rates of shoulder retraction, positional plagiocephaly, and positional torticollis. 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. A research study on children with plagiocephaly 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.

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.

Additional studies have found the following negative conditions that the back sleep position has been reported to be associated with are: Increase in Sleep Apnea, Decrease in Sleep Duration, Strabismus, Social Skills Delays, deformational plagiocephaly, and Temporomandibular Jaw Difficulties. 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. 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. 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. Supine sleeping infants cannot self-treat their own torticollis.

Notes

1989 "Sleep and Arousal Synchrony of Co-Sleeping Human Mother-Infant Pairs: Implications for the Study of SIDS." Fourth World Congress of Infant Psychiatry and Allied Disciplines (poster session). Lugano, Switzerland. Presented also at 58th Annual Meeting, American Association of Physical Anthropologists.
1989 "Why Anthropologists Should Study SIDS." Annual Meeting of the Southwest Anthropological Society. Riverside, California, April.
1988 "Sleep and Breathing Patterns of Co-Sleeping Mothers and Infants." Eighty-seventh Meeting of the American Anthropological Association. Chicago, Illinois, November 19-23.
1986 "Can Parents Drive the Breathing of Their Infants? Evolutionary and Developmental Hypotheses on Contributing Environmental Factors in Sudden Infant Death." Third World Congress on Infant Psychiatry and Allied Disciplines. Stockholm, Sweden, August 3-7.