Sleeping position and sudden infant death syndrome in Norway 1967-91

Trends in infant mortality: an evaluation of forensic autopsied infants in Eastern Denmark over 39 years

BACKGROUND

SIDS is a diagnosis of exclusion applied to the death of an infant < 1 year of age after an extensive post-mortem investigation. From 1980 to 2018, a total of 870 infants have been autopsied at the Section of Forensic Pathology, Department of Forensic Medicine, UCPH, covering East Denmark. In the same period, Danish national guidelines for infant care have been revised to avoid infants dying of SIDS.

OBJECTIVE

This study aimed to describe trends in infant autopsies regarding cause and manner of death, gender, age, month of death, sleeping position, and bed-sharing. The trends were compared to the change in national SIDS guidelines during the period of this study.

DESIGN

Information from autopsy reports from 1980 to 2018 were collected into 55 categories designed specifically for this study. Data from 7 of these categories were chosen and processed in Excel for basic epidemiological comparison.

RESULTS

The trends show that most infants in the study die of natural manner and most predominant causes of death are SIDS, infection, and congenital malformations. A change in national guidelines in 1991 recommending supine- or side sleeping position coincided with a reduction in the overall infant mortality and cases of SIDS. The peak age in the cohort is 90 days, but stratification in decades shows the infants dying younger each decade. Through the study period, the number of infants found dead sleeping in the prone position has declined. Relatively more infants in this cohort have been found dead while bed-sharing, even though the prevalence of these cases has remained largely the same for four decades.

[Gastroesophageal reflux and sleep position of infants. A survey conducted in France by 493 pediatricians]

BACKGROUND AND AIMS

The supine sleeping position with the head higher than the legs has no impact on regurgitations in infants. Inclined ventral decubitus decreases regurgitations but is associated with an increased risk of sudden infant death syndrome (SIDS). The LUNE study aimed to evaluate the impact of regurgitations on the choice of sleeping position by pediatricians and parents.

METHODS

Cross-sectional case-control study (ratio 1:1) conducted in France in 2013. A representative sample of pediatricians recruited 3-week to 4-month-old breast- or formula-fed infants. Cases and controls were defined by the presence or absence of regurgitations. Collected data included Vandenplas codification for regurgitations (VD, range 0-6), associated symptoms, and variations in sleeping position since maternity hospital discharge.

RESULTS

A total of 1347 cases and 1346 controls were recruited by 493 pediatricians. Regurgitations were evaluated at VD1 (minor, 22 % of cases), VD2 (mild, 47 % of cases), or VD≥3 (moderate to severe, 31 % of cases). At the maternity hospital, the supine position was recommended to 96 % of parents for SIDS prevention. Since discharge, parents asked questions about the relationship between sleeping position and regurgitations (79 % of infants with GER versus 45 % of controls). The sleeping position was modified at least once since maternity discharge (42 % of infants with GER versus 35 % of controls). At inclusion, 86 % of infants with GER and 86 % of controls were sleeping on their back. Fifty-one percent of infants with GER and 28 % of controls slept in an inclined position. Pediatricians repeated the prescription of dorsal decubitus for 91 % of infants with GER and recommended an inclined position in 70 %.

CONCLUSIONS

Regurgitations had no impact on supine sleeping position. The inclined supine sleeping position was more frequent in infants with regurgitations with pediatricians' assent, which is not in agreement with evidence-based medicine.

Hypothesis on supine sleep, sudden infant death syndrome reduction and association with increasing autism incidence

AIM: To identify a hypothesis on: Supine sleep, sudden infant death syndrome (SIDS) reduction and association with increasing autism incidence.

METHODS: Literature was searched for autism spectrum disorder incidence time trends, with correlation of change-points matching supine sleep campaigns. A mechanistic model expanding the hypothesis was constructed based on further review of epidemiological and other literature on autism.

RESULTS: In five countries (Denmark, United Kingdom, Australia, Israel, United States) with published time trends of autism, change-points coinciding with supine sleep campaigns were identified. The model proposes that supine sleep does not directly cause autism, but increases the likelihood of expression of a subset of autistic criteria in individuals with genetic susceptibility, thereby specifically increasing the incidence of autism without intellectual disability.

CONCLUSION: Supine sleep is likely a physiological stressor, that does reduce SIDS, but at the cost of impact on emotional and social development in the population, a portion of which will be susceptible to, and consequently express autism. A re-evaluation of all benefits and harms of supine sleep is warranted. If the SIDS mechanism proposed and autism model presented can be verified, the research agenda may be better directed, in order to further decrease SIDS, and reduce autism incidence.

Salivary cortisol and administration of concentrated oral glucose in newborn infants: improved detection limit and smaller sample volumes without glucose interference

Newborn infants are subject to repetitive painful and stressful events during neonatal intensive care. When the baby attempts to cope with a stressful situation the hypothalamus-pituitary-adrenal axis is activated, releasing cortisol. The free cortisol response is optimally measured in saliva and saliva samples can be taken easily and without pain. However, saliva is very scarce in infants and saliva stimulants can interfere with analytical methods. Nowadays, sweet solutions are frequently administered to neonates prior to a disturbing procedure in order to reduce pain. The possible interference of sweet solutions with the measurement of salivary cortisol has not yet been documented. The aims of the present study were to further improve the detection limit of the radioimmunoassay used for cortisol analysis and to determine the degree of interference of high concentrations of glucose with the analytical method. By decreasing incubation temperature and prolonging the incubation time it was possible to improve the detection limit of the radio immunoassay (RIA) to 0.5 nmol/L at the same time as the sample volume was decreased to 10 microL saliva. Saliva was collected from full-term and preterm babies and was sufficient for analysis in 113 out of 116 (97%) samples. Glucose in the concentrations and amounts commonly used for pain relief did not interfere with the RIA method. In conclusion, it is feasible to collect microlitre volumes of saliva and analyse even very low concentrations of cortisol in newborns. It is also possible to offer the baby oral glucose prior to a painful procedure and still reliably measure salivary cortisol.

Mortality patterns in geographical areas with a high vs. low Sami population density in Arctic Norway

AIMS

The aim of this study was to study mortality patterns in the population in different geographical locations in northern Norway on the basis of Sami population density.

METHODS

Mortality statistics by sex and age from 1991 to 2006 were obtained from Statistics Norway. Mortality rates, including infant mortality rates, were compared across geographical locations. The data material was divided into within and outside the the geographical areas of the Sami Development Fund (SUF) and into coastal and inland residence. Differences in mortality rates were tested by chi-quadrate tests.

RESULTS

Overall, no pronounced difference in mortality rate was found in the population between geographical areas. For men, mortality rates differed only between geographical residence in the time intervals 1991-95 and 1996-2000 for the age groups 45-59 years and 60-74 years, respectively, with outside SUF area, inland having the lowest rate. For women, there were no differences between geographical areas except for the age group 60-74 years in the time period 1991-95, where SUF coast had the highest mortality rate. For the SUF area, men had the lowest probabilities for surviving the age of 74 years and women had among the highest. No geographical difference was found in infant mortality. During the time period 1991-2006, the outside SUF area, inland had an average infant mortality rate of 1.8/1000 per year, and for SUF coast it was 6.2/1000 per year. This difference was, however, not significant (p = 0.08).

CONCLUSIONS

Overall, mortality rates were similar across geographical areas with low and with high Sami population density. However, indications of geographical differences in infant mortality should be investigated further.

Post-neonatal mortality in Norway 1969-95: a cause-specific analysis

BACKGROUND

We recently reported increased social inequality for post-neonatal death. The aim of the present study was to investigate the association between socioeconomic status and cause-specific post-neonatal death.

METHODS

All 1,483,857 live births recorded in the Medical Birth Registry of Norway from 1969-95 with information on parents' education were included. During the post-neonatal period (from 28 to 364 days of life) 4,464 infants died. Differences between education groups were estimated as risk differences, relative risks, population attributable fractions, and relative index of inequality.

RESULTS

The major causes of death were congenital conditions, sudden infant death syndrome (SIDS), and infections. Post-neonatal mortality declined from 3.2/1,000 in the 1970s to 1.9/1,000 in the 1990s, mainly due to reduced mortality from congenital conditions. The absolute risk for SIDS increased by 0.51/1,000 in the same period among infants whose mothers had low education, while it decreased by 0.56/1,000 for those whose mothers had high education. The relative risk for SIDS among infants whose mothers had low education increased from 1.02 in the 1970s to 2.39 in the 1980s and 5.63 in the 1990s. Among infants whose fathers were not recorded in the Birth Registry, the absolute risk of SIDS increased by 0.79/1,000 from the 1970s to the 1990s.

CONCLUSIONS

Increased social inequality for post-neonatal death was primarily due to increases in the absolute and relative risks of SIDS among infants whose mothers have low education. Social inequality widened during the study period for SIDS and deaths caused by infections.

Infant sleeping position and the sudden infant death syndrome: systematic review of observational studies and historical review of recommendations from 1940 to 2002

BACKGROUND

Before the early 1990s, parents were advised to place infants to sleep on their front contrary to evidence from clinical research.

METHODS

We systematically reviewed associations between infant sleeping positions and sudden infant death syndrome (SIDS), explored sources of heterogeneity, and compared findings with published recommendations.

RESULTS

By 1970, there was a statistically significantly increased risk of SIDS for front sleeping compared with back (pooled odds ratio (OR) 2.93; 95% confidence interval (CI) 1.15, 7.47), and by 1986, for front compared with other positions (five studies, pooled OR 3.00; 1.69-5.31). The OR for front vs the back position was reduced as the prevalence of the front position in controls increased. The pooled OR for studies conducted before advice changed to avoid front sleeping was 2.95 (95% CI 1.69-5.15), and after was 6.91 (4.63-10.32). Sleeping on the front was recommended in books between 1943 and 1988 based on extrapolation from untested theory.

CONCLUSIONS

Advice to put infants to sleep on the front for nearly a half century was contrary to evidence available from 1970 that this was likely to be harmful. Systematic review of preventable risk factors for SIDS from 1970 would have led to earlier recognition of the risks of sleeping on the front and might have prevented over 10 000 infant deaths in the UK and at least 50 000 in Europe, the USA, and Australasia. Attenuation of the observed harm with increased adoption of the front position probably reflects a "healthy adopter" phenomenon in that families at low risk of SIDS were more likely to adhere to prevailing health advice. This phenomenon is likely to be a general problem in the use of observational studies for assessing the safety of health promotion.

Effect of religious observance on infants' sleep position in the Jewish population

OBJECTIVES

To describe the effect of the level of religiousness on infants' sleep position in the Jewish population.

METHODS

A longitudinal telephone survey of randomly selected 608 2-month-old Jewish infants repeated at 4 and 6 months. Results were analyzed versus the four levels of Jewish religion observance.

RESULTS

A significant correlation was found between the level of religious practice and sleep position (P < or = 0.002). 56.8% (50/88) of ultra-orthodox parents put their babies to sleep in the non-prone position, compared with 79% (411/520) in the other three groups (P < 0.001). Non-prone sleeping decreased when infants grew. Higher parity correlated with the level of religiousness and with prone sleeping in religious families (OR = 1.15, 95% CI 1.00-1.33, P < 0.001).

CONCLUSIONS

Jews and especially the ultra-orthodox families comply significantly less with recommendations to avoid prone sleeping. Specific measures may be required in this population that rely more on personal experience and belief than on health care provider advice.

Maternal and obstetric risk factors for sudden infant death syndrome in the United States

OBJECTIVE

The objectives of this study were to 1). study the incidence of sudden infant death syndrome (SIDS) among singleton births in the United States and 2). identify maternal and obstetric risk factors for SIDS.

METHODS

A cohort of all live births in the United States from 1995 to 1998, formed the source population (n = 15627404). The data were obtained from the National Centers for Health Statistics Linked Births and Infant Deaths File. A nested case-control study was used to examine risk factors for SIDS. From this birth cohort, all SIDS deaths (n = 12404) were first identified (case group). From the remaining non-SIDS births, a 4-fold larger sample (n = 49616) was randomly selected as a control group.

RESULTS

The overall incidence of SIDS was 81.7 per 100000 live births. More mothers in the case group than in the control group were reported to have placenta previa (odds ratio [OR]: 1.70; 95% confidence interval [CI] 1.24, 2.33), abruptio placentae (OR 1.57; 95% CI 1.24, 1.98), premature rupture of membranes (OR 1.48; 95% CI 1.33, 1.66), or small for gestational age (OR 1.40; 95% CI 1.30, 1.50 for the 10th percentile). SIDS cases were also more likely to be male. Mothers of cases were more likely to be younger, less educated, and nonwhite, and more of them smoked during pregnancy and did not attend prenatal care.

CONCLUSION

This analysis confirms the importance of several well known demographic and lifestyle risk factors for SIDS. In addition, placental abnormalities were risk factors for SIDS.

LEVEL OF EVIDENCE

II-2

Secular changes in sleep position during infancy: 1995-1998

OBJECTIVE

Prone sleeping among infants has been associated with an increased risk of sudden infant death syndrome. The objective of this study was to compare factors associated with sleep position in 1995-1996 and 1997-1998 and to assess secular trends in use of prone infant sleep position from 1995 through 1998 among families stratified by race and education.

METHODS

A prospective cohort study was conducted in eastern Massachusetts and northwest Ohio of 12 029 mothers of infants who weighed > or =2500 g at birth. Descriptive statistics and multivariate odds ratios were used to relate maternal and infant characteristics to prone and supine sleeping.

RESULTS

A total of 14 206 mothers (25% of those eligible) were enrolled. A total of 12 029 mothers (85% of enrolled) responded to the 1-month and 11 552 mothers (81% of enrolled) responded to the 3-month follow-up questionnaire. A decline in use of the prone sleep position and increase in use of the supine position was observed during the 4 years of the study. Factors associated with prone and supine sleep position were similar in 1995-1996 and 1997-1998. In 1997-1998, use of prone sleeping at 1 month of age reached the goal of < or =10% only among infants of white and Asian women, married women, women who were older than 25 years, women who were college graduates, and women with incomes >$55 000 per year. At 3 months of age, however, prone sleeping increased to 12% to 17% in these groups. These same groups were most likely to use the supine position; 38% to 45% were supine at 1 month, increasing to 56% to 64% by 3 months of age. However, as of the end of 1998, approximately 27% of infants of non-college-educated black and Hispanic mothers were placed to sleep in the prone position and only 20% to 30% were being placed to sleep in the supine position at 3 months of age.

CONCLUSIONS

Recommendations to avoid prone sleep position and especially the recommendation that supine sleep position is preferred have not been effectively delivered to black and Hispanic families and to families of low-income and less than a college education.

Determinants of infant sleep position in an urban population

The incidence of SIDS has decreased by 40% since the Back to Sleep campaign was initiated. However, the rate of SIDS in the District of Columbia continues to be approximately double the national rate. The purpose of this study was to determine the prevalence and determinants of prone sleeping among infants in the District of Columbia and to ascertain what information is being provided to parents by health care professionals by a cross-sectional survey of parents of infants 0-6 months of age presenting for well child care at Children's Health Center, Children's National Medical Center, in Washington, DC. We recruited a consecutive sample of 126 parent-infant pairs, of which 92.9% were African-American. The average infant was 73 days old, was 3,003 grams at birth, and was full term. When asked how the infants were placed for sleep the night before the interview, 34.1 % of parents had placed the infant supine, 50.8% side, and 15.1% prone. Nearly half (48%) of infants slept in an adult bed with the mother. More than one third of the infants had been placed prone for sleep at least once since hospital discharge. Most common reasons for sleeping supine included SIDS risk reduction or health care professional advice. Side sleepers did so primarily because of concern about vomiting, health care provider advice, or SIDS. Infants were placed prone primarily because the infant slept better. When asked about information received from a health care provider, 70.6% of parents stated that they had received information about sleep position and 64.3% about the hazards of passive smoking. Eight parents observed nursery personnel placing their infants prone. Only 16.7% of the total study population had received a Back to Sleep brochure, read it, and recalled that it recommended back sleeping. Infants were more likely to sleep prone if there was a grandparent in the home (OR 2.9, p<0.05) or if they were the firstborn (OR 2.17, p<0.05). Infants were more likely to sleep supine if parents had heard a back recommendation from a health care professional (OR 5.7, p<0.001). Infants were least likely to sleep supine if the parents had heard a side or a side/back recommendation (OR 0.26, p=0.001). Infant sleep position was not ter, reading the Back to Sleep brochure. In conclusion, more than one third (35.7%) of infants in this predominantly African-American population have been placed prone for sleep at least once; 15% slept prone the night before the interview. Almost one third of parents received no information about sleep position, but parents receiving a verbal supine recommendation were most likely to place their infant supine. Receiving written information did not affect sleep position. Improved educational efforts for parents of African-American newborns should continue to focus on encouraging supine positioning, smoke cessation, and other safe sleep practices.

Population trends in sudden infant death syndrome

This review documents and assesses recent trends in sudden infant death syndrome. We review medical literature, Internet resources, and national governmental data. A striking reduction in SIDS incidence of more than 50% has been observed in various countries after interventions, particularly during the early 1990s, to reduce the prevalence of prone infant sleeping. A reduction in postneonatal mortality has accompanied these lower rates. Evaluation studies from several countries indicate that the SIDS rate drop is largely attributable to a decline in the proportion of babies sleeping prone. Within countries, the SIDS rate decline has not occurred to the same extent for different ethnic and socio-economic groups. Future public health activities must aim to address this issue. In the post-intervention era, the relative importance of the risk factors of side compared to supine sleeping and soft bedding near the infant's airway have become more evident. Recent death scene data indicate that a substantial proportion of the remaining SIDS deaths could be avoided by supine sleeping and by providing a safe sleeping environment for all infants.

Physician beliefs and practices regarding SIDS and SIDS risk reduction

The AAP has alerted pediatricians to the importance of safe sleep environment for infants. The elements of a safe sleep environment include supine sleep position, safe crib, and avoidance of smoke exposure, soft bedding, and overheating. With the Back to Sleep campaign, prone sleeping among all U.S. infants has decreased to less than 20%, and the incidence of SIDS has decreased 40%. However, the decline in SIDS and prone sleeping has leveled off in recent years. Further declines may be possible with decreasing other modifiable risk factors, such as prenatal and postnatal exposure to cigarette smoking. Prior studies have demonstrated that health care professional advice is influential in determining infant care practices. It is important that physicians caring for infants be aware of the importance of a safe sleep environment and understand other modifiable risk factors for SIDS. We surveyed a random sample of 3,717 physicians in North Carolina and the metropolitan Washington, DC, area to determine knowledge, beliefs, and practices regarding SIDS and SIDS risk reduction among physicians caring for pregnant women and infants. Twenty-three percent (835) responded. Most physicians are aware of prone sleeping and cigarette smoke exposure as risk factors for SIDS. Almost all physicians agree that there are measures that can be taken to reduce the risk of SIDS, and they consider it important to discuss SIDS and SIDS risk reduction strategies with parents of young infants. In spite of this belief, only 56% of family/general practitioners, 18% of obstetrician-gynecologists, and 79% of pediatricians discuss SIDS routinely. Only 35% of pediatricians, 15% of family/general practitioners, and 16% of obstetrician-gynecologists provide written information. In addition, only 38% of physicians recommend supine, while 50% recommend side or back, 6% side, and 7% prone. Only two thirds of pediatricians and one third of family/general practitioners are aware that the AAP recommends supine as the preferred sleep position for infants. Pediatricians are more likely to be aware of the AAP recommendation (p<0.0001) and to discuss SIDS risk reduction strategies with parents (p=0.03). We conclude that many physicians who care for infants are unaware of the AAP's most current recommendation for sleep position and are incorrectly recommending the side position. Physicians may also be unaware of other sleep environment hazards. Further educational efforts must continue for physicians who provide care to pregnant women and children to ensure a continued decline in the incidence of SIDS.

Evaluation of diagnostic tools applied in the examination of sudden unexpected deaths in infancy and early childhood

During the period between 1984 and 1999, 309 cases of sudden unexpected death in infancy and early childhood (0-3 years) were investigated at the Institute of Forensic Medicine in Oslo. In 73 cases, an explainable cause of death was found. In this non-sudden infant death syndrome (SIDS) group, 42 cases were due to disease, 14 to accidents, 7 to neglect/abuse and 10 cases were due to homicide. In 43 cases, there were pathological findings at the autopsy or suspect features in the history and/or circumstances, which were, however, insufficient to explain death ("borderline" SIDS). In the remaining 193 cases, nothing of significance was detected ("pure" SIDS). The purpose of the present study was to evaluate the importance of the different diagnostic tools used in diagnosing non-SIDS and borderline SIDS cases. The definition of SIDS requires a negative history as well as a negative autopsy result. Thus, the following variables were analysed: circumstances, medical history and autopsy, which included a gross pathological investigation, histology, neuropathology, microbiology, radiology and toxicology. In diagnosing deaths due to disease, histology, neuropathology and microbiology were the most important diagnostic tools. In contrast, information about the circumstances of death and the gross pathological findings at autopsy most often revealed the cause of death in accidents and cases of neglect/abuse and homicide. Following the drop in SIDS rate in Norway after 1989, the share of pure SIDS in proportion to the total population of sudden unexpected deaths in infancy and early childhood has decreased. The increasing proportion of non-SIDS and borderline SIDS cases presents a challenge to improve the quality of the investigation in cases of sudden death in infancy and early childhood.

Parallel incidences of sudden infant death syndrome and infantile hypertrophic pyloric stenosis: a common cause?

OBJECTIVE

To determine whether there was a correlation between the incidence of infantile hypertrophic pyloric stenosis (IHPS) and the incidence of sudden infant death syndrome (SIDS) during the period 1970 to 1997 and to discuss different causative factors that could be influencing the changing trend in incidence.

METHODS

We compared the incidence of IHPS in the Stockholm Health Care Region with the incidence of SIDS in Sweden each year between 1970 and 1997. First, the relation was assessed by calculation of a correlation coefficient; second, the relative linear decrease was estimated for the time period 1990 to 1997.

RESULTS

The incidence of IHPS increased steadily during the 1970s, from 0.5 per 1000 live births in 1970 to 2.7 in 1979. During the 1980s, the average incidence was 2.8. During the 1990s, there was a significant decrease in the number of IHPS cases in Stockholm. The incidence rate of IHPS parallels the incidence of SIDS during the study period (r = 0.58). The incidence of SIDS dropped after the risk-reduction campaign in the beginning of the 1990s, which recommended that infants sleep on their back. We could not identify any other changes of behavioral risk factors in early exposures that could explain the temporal trends.

CONCLUSIONS

The statistical findings suggest that IHPS and SIDS have causative factors in common. We suggest that prone sleeping is one of those factors.

Changes in the epidemiological pattern of sudden infant death syndrome in southeast Norway, 1984-1998: implications for future prevention and research

AIM

To look for changes in risk factors for sudden infant death syndrome (SIDS) after decrease and stabilisation of the SIDS rate.

METHODS

Questionnaires were distributed to parents of 174 SIDS infants, dying between 1984 and 1998, and 375 age and sex matched controls in southeast Norway.

RESULTS

The proportion of infants sleeping prone has decreased, along with the decrease in SIDS rate for the region during the periods studied, but over half of the SIDS victims are still found in the prone position. As the number of SIDS cases has decreased, additional risk factors have become more significant. Thus, after 1993, a significantly increased risk of SIDS is seen when the mother smokes during pregnancy. After 1993, young maternal age carries an increased risk. Maternal smoking and young maternal age are associated with each other. For SIDS victims, an increase in the number of infants found dead while co-sleeping is seen, and the age peak between 2 and 4 months and the winter peak have become less pronounced.

CONCLUSION

Changes in risk factor profile following the decrease in SIDS rate in the early 1990s, as well as consistency of other factors, provides further clues to SIDS prevention and to the direction of further studies of death mechanisms.

Assessment of dry heat exchanges in newborns: influence of body position and clothing in SIDS

A dramatic decrease of sudden infant death syndrome (SIDS) has been noted following the issuance of recommendations to adopt the supine sleeping position for infants. It has been suggested that the increased risk could be related to heat stress associated with body position. In the present study, the dry heat losses of small-for-gestational-age newborns nude or clothed were assessed and compared to see whether there is a difference in the ability to lose heat between the prone and supine positions. An anthropomorphic thermal mannequin was exposed to six environmental temperatures, ranging between 25 and 37 degrees C, in a single-walled, air-heated incubator. The magnitudes of heat losses did not significantly differ between the two body positions for the nude (supine 103.46 +/- 29.67 vs. prone 85.78 +/- 34.91 W/m(2)) and clothed mannequin (supine 59.35 +/- 21.51 vs. prone 63.17 +/- 23.06 W/m(2)). With regard to dry heat exchanges recorded under steady-state conditions, the results show that there is no association between body position and body overheating.

Review of risk factors for sudden infant death syndrome

Sudden infant death syndrome (SIDS) accounts for the largest number of deaths during the first year of life in developed countries. The possible causes of SIDS are numerous and, to date, there is no adequate unifying pathological explanation for SIDS. Epidemiological studies have played a key role in identifying risk factors, knowledge of which has underpinned successful preventive programmes. This review critically assesses information on the main risk factors and causal hypotheses put forward for SIDS, focusing on research published since 1994. The overall picture that emerges from this review is that affected infants are not completely normal in development, but possess some inherent weakness, which may only become obvious when the infant is subjected to stress. Initially there may be some minor impairment or delay in development of respiratory, cardiovascular or neuromuscular function. None of these is likely to be sufficient, in isolation, to cause death and, provided the infant survives the first year of life, may no longer be of any significance. However, when a compromised infant is confronted with one or more stressful situations, several of which are now clearly identified as risk factors, and from which the majority of infants would normally escape, the combination may prove fatal.

Changes in the epidemiology of sudden infant death syndrome in Sweden 1973-1996

BACKGROUND

From the early 1970s to the early 1990s, there was a significant rise in the incidence of sudden infant death syndrome (SIDS) in Scandinavia. Following the risk reducing campaign, the incidence has fallen to about the same level as in 1973.

AIMS

To identify the changes that have occurred in the epidemiology of SIDS.

METHODS

We compared the Swedish part of the Nordic Epidemiological SIDS Study (NESS), covering the years 1992-1995, with two earlier, descriptive studies during this period. To assess the changing effects of risk factors, we analysed data from the Medical Birth Registry of Sweden, covering the years 1973-1996.

RESULTS

There was a predominance of deaths during weekends in the 1970s and 1990s. The seasonal variation was most notable in the 1980s. The proportion of young mothers decreased from 14% to 5%. Cohabitation (living with the biological father) was as frequent in the 1990s as in the 1970s. The prevalence of high parity, admissions to neonatal wards, low birth weight, prematurity, and multiple pregnancies were all increased in the 1990s compared to the 1970s. No significant change in the prevalence of previous apparent life threatening events was found. Deaths occurring in cars diminished from 10% to below 2%. In the data from the Medical Birth Registry of Sweden, there were significantly increased odds ratios after the risk reducing campaign of the risk factors smoking during early pregnancy and preterm birth. We could find no increased effects of maternal age, parity, or being small for gestational age over time. The rate of deaths at weekends remained increased; the median age at death fell from 90 to 60 days. Seasonal variation was less notable in the periods of low incidence.

The healthy human infant tends to sleep in the prone rather than the supine position

There are few reports about developmental behavior relating to roll over among healthy infants. We assessed the relationship between the placed position on sleeping and altered sleeping position the next morning by roll over among healthy infants. A health check-up clinic distributed a total of 1626 questionnaires to parents whose infant's ages are 1.5 years (or 18 months) old. The age at the first roll over and the change in sleeping position the next morning after they started to roll over, were investigated. The mean age of roll over from the supine to the prone among infants who were placed mainly in the prone sleeping position, at least in the first week of life, was 4.0 months (S.D., 1.1). The mean age of roll over from the supine to the prone among infants who were placed mainly in the supine sleeping position during early neonatal life and thereafter was 4.4 months (S.D., 1.2). The age of the first roll over from supine to prone was significantly younger in infants who were placed mainly in the prone sleeping position during early neonatal life. Among 651 infants who had been placed supine, 34.7% were found prone by roll over the next morning. Among 211 infants who had been placed prone, 14.2% were found supine by roll over the next morning. The number of infants who rolled over from supine to prone position was statistically greater than those from prone to supine. It is likely that the healthy human infant tends to sleep in the prone rather than the supine position. The finding is especially important for the correct assessment of the position in which SIDS cases were found dead.

Changing concepts of sudden infant death syndrome: implications for infant sleeping environment and sleep position. American Academy of Pediatrics. Task Force on Infant Sleep Position and Sudden Infant Death Syndrome

The American Academy of Pediatrics has recommended since 1992 that infants be placed to sleep on their backs to reduce the risk of sudden infant death syndrome (SIDS). Since that time, the frequency of prone sleeping has decreased from >70% to approximately 20% of US infants, and the SIDS rate has decreased by >40%. However, SIDS remains the highest cause of infant death beyond the neonatal period, and there are still several potentially modifiable risk factors. Although some of these factors have been known for many years (eg, maternal smoking), the importance of other hazards, such as soft bedding and covered airways, has been demonstrated only recently. The present statement is intended to review the evidence about prone sleeping and other risk factors and to make recommendations about strategies that may be effective for further reducing the risk of SIDS. This statement is intended to consolidate and supplant previous statements made by this Task Force.

Sudden infant death syndrome--are parents getting the message?

BACKGROUND

Factors that place an infant at increased risk of sudden infant death include the prone sleep position, overheating and parental smoking, while practices such as bottle-feeding, co-sleeping and the use of pacifiers remain controversial. Major publicity campaigns have been undertaken, which have included the distribution of printed material and extensive media coverage.

AIMS

To examine if Irish parents follow the currently recommended childcare guidelines to reduce the risk of sudden infant death and to examine factors that may have impact on their acceptance.

METHODS

A random selection of 197 infants from the Birth Register of the Eastern Health Board. Parents were interviewed and a semi-structured survey questionnaire was completed.

RESULTS

Forty one per cent of infants are still placed on their side to sleep, an inherently unstable position. First time parents are more likely to place their infants on their backs. Over 60% of infants are exposed to one or more adults smoking in the home despite parental knowledge of its association with sudden infant death syndrome (SIDS). Sixty eight per cent of infants are overwrapped at night and parental understanding of what constitutes overwrapping is poor. Thirteen per cent of infants regularly co-sleep with their parents and 20% of these parents smoke. Pacifier use is common.

CONCLUSION

Future programmes should target first time parents, should provide clear information regarding appropriate infant thermal environment, and should ensure regular updating of medical personnel so that they can instruct families on best current practice. Smoking remains a significant health issue with an impact on sudden infant death.

Infant care practices in a metropolitan aboriginal population Bibbulung Gnarneep Team

OBJECTIVE

To describe sleeping position, room and bed-sharing, tobacco smoke exposure and infant feeding for a sample of Australian Aboriginal infants from a metropolitan area.

METHODS

Interviews with Aboriginal mothers who resided in the Perth metropolitan area and had given birth during a continuous 15-month study period. The interviews took place when the infants were approximately 6-12 weeks old and efforts were made to contact all eligible mothers. Results are presented as proportions with 95% confidence intervals.

RESULTS

Of all the eligible mothers (n = 515), 87% were contacted and 53% (n = 273) completed the interview. Of all the infants, 11% slept prone, 96% shared a room and 68% shared a bed; 65% of mothers smoked during pregnancy and 65% were smokers at the time of interview; 66% of the partners were smokers and 80% of the infants were regularly exposed to tobacco smoke; 89% of mothers initiated breast-feeding and 70% were breast-feeding at time of interview.

CONCLUSION

Prevalences of non-prone sleeping and breast-feeding are similar to the overall Western Australian population, whilst tobacco smoke exposure of the infants is markedly higher. Programs of community and family education and support are required urgently to decrease this exposure.

Sudden infant death syndrome: what questions should we ask?

A limited historical perspective can affect the questions we pose about the sudden infant death syndrome (SIDS) issue. Evidence is presented from the literature that the SIDS rate in Western countries was low prior to World War II and peaked in the 1980s. An analogy is drawn with the trends in the prevalence of some infectious diseases, and questions are posed from the perspective of a bacterial toxin hypothesis of SIDS causation.

Inflammatory responses in sudden infant death syndrome -- past and present views

Sudden infant death syndrome (SIDS) is sudden unexpected death in infancy for which there is no explanation based on commonly accepted diagnostic criteria; however, half of the victims have had slight signs of infection prior to death. Such slight infection with fever is an important risk factor in combination with a prone sleeping position, especially in infants between 2 and 4 months of age. The purpose of this review is to summarise findings that support the theory that a significant part of cot deaths may be due to an overreaction to otherwise harmless infections. Such factors are mucosal immune stimulation, cytokines in the cerebrospinal fluid and hypoxanthine levels in vitreous humour. The review aims at explaining why we believe that a slight infection combined with a prone position, a warm environment and a vulnerable age period may trigger a vicious circle leading to death.

Sleeping position in infants over 6 months of age: implications for theories of sudden infant death syndrome

The aim of this study was to determine the prevalence of prone and supine sleeping in infants aged 0-12 months and relate this to changes in the number of cases of sudden infant death syndrome (SIDS) since 1985. Seventy-two babies, 38 male and 34 female, were followed for the first 18 months of life with regular home visits and sleeping position was recorded. In addition, data on the number of cases of SIDS in England and Wales between 1985 and 1995 were analysed. All babies slept supine for the first 5 months of life, but once they could turn over in their cots (mean age 7.34 months, range 5-11 months) the majority slept prone. By 11 months of age, 53 regularly slept prone (73%), 95% CI +/- 19.8%), while 11 slept supine, three adopted the side position and five varied from night to night. The number of cases of SIDS in infants aged 7-11 months has fallen significantly (P<0.0001) in a period in which the prevalence of prone sleeping, in that age group, has not changed. The most plausible explanation for this paradoxical result is that supine sleeping in the first 5 months of life reduces the absolute risk of SIDS in the second 6 months of life even though most babies are then sleeping prone. It is suggested that reduced exposure to nasopharyngeal bacterial superantigens in babies sleeping prone might explain this effect.

Secular trends in breastfeeding and parental smoking

To explore the association between smoking and breastfeeding, we obtained data from a retrospective questionnaire-based national survey comprising a random sample (n = 34799) of all mothers giving birth in Norway 1970-91. Variables studied were postpartum smoking habits for both parents, duration of breastfeeding, infant's year of birth and parental age. The response rate was 70% (n = 24438). During the study period, the maternal postpartum smoking prevalence decreased from 38% to 26%. The proportion breastfeeding at 6 months increased from 15% to 44% among smokers, and from 30% to 72% among non-smokers. In spite of a considerable increase in breastfeeding both among smokers and non-smokers, the proportion of breastfeeding, non-smoking women at 6 months was twice that of smoking women during the whole period. Furthermore, the duration of breastfeeding was shorter among young mothers and when the fathers were smoking. There was epidemiological evidence that the effect on breastfeeding of smoking might represent both biological and social mechanisms.

Sudden unexpected infant death syndrome in Ribeirão Preto, Brazil

CONTEXT

Sudden Infant Death Syndrome (SIDS) is the leading cause of death in the first year of life in developed countries. Brazilian and Latin American literature lack studies on the subject, which is largely unknown among health workers.

OBJECTIVE

To identify cases that could be classified as SIDS among children of less than one year of age submitted to autopsy at the Serviço de Verificação de Obitos do Interior (SVOI), in Ribeirão Preto, SP, Brazil. A retrospective analysis of all autopsies from SVOI in this age group from January 1987 to December 1990 was done.

RESULTS

There were 369 autopsies of which 344 (93.2%) deaths were expected and 25 (6.8%) unexpected. From the 25 unexpected cases 16 (64%) deaths could not be explained after autopsy and from these cases only 10 were eligible for the study because they had full organ sampling. There were 7 males and 3 females and the age at death ranged from 1 to 3 months (average: 1.7 months). Two were found dead, 3 died at home, 4 died on the way to hospital and 1 died while being fed. Autopsy diagnoses were aspiration (8 cases), SIDS (1 case) and undetermined (1 case). Aspiration was not confirmed by histology and the only findings were mild pulmonary edema, subcapsular petechiae and intraparenchymatous hemorrhage in thymus.

CONCLUSION

That there were 10 cases of unexpected and unexplained deaths of children less than 1 year-old during the evaluated period with characteristics similar to SIDS which should therefore be classified as such.

SIDS--changes in the epidemiological pattern in eastern Norway 1984-1996

The objective was to analyse differences in the epidemiological pattern of sudden death in infancy during two time periods--the Sudden Infant Death Syndrome (SIDS) 'epidemic': 1984-1989, and the period of rapid decline in the SIDS rate 1990-1996. Sex distribution, age, sleeping position, signs of infection, day of the week and place of death were registered and compared for the two time periods studied in all SIDS cases autopsied at the Institute of Forensic Medicine, Oslo. There were significantly more deaths in the age group under four months in the period 1984-89 than in the second period. Prone sleeping position, signs of infection, death outdoors and during the winter were more frequent during the first period than in the second. These features also were more frequent in the age group under four months than in the older babies during the first period. The shift in the epidemiological pattern after 1990, when the risk factor campaign was launched, indicates that prone sleeping position, cold climate, sleeping outdoors and infections seem to be risk factors that are particularly harmful to the youngest infants.

Combined effects of sleeping position and prenatal risk factors in sudden infant death syndrome: the Nordic Epidemiological SIDS Study

OBJECTIVE

Prone sleeping is a strong risk factor for sudden infant death syndrome (SIDS). We investigated whether the combined effect of prone sleeping position and prenatal risk factors further increased the SIDS risk.

METHODS

In the Nordic Epidemiological SIDS Study, parents of SIDS victims in Denmark, Norway, and Sweden completed a questionnaire on potential risk factors for SIDS. Forensic pathologists verified the SIDS diagnosis. Four controls of the same gender, age, and place of birth were selected. This matched case-control study, which included 244 SIDS cases and 869 controls from 1992 to 1995, was analyzed by conditional logistic regression.

RESULTS

Odds ratios (ORs) for prone and side sleeping compared with supine sleeping for the last sleep were 13.9 (95% confidence interval 8.2-24) and 3.5 (2.1-5.7). Infants 13 to 24 weeks old had particularly high risk in prone and side sleeping, at 28.5 (7.9-107) and 5.9 (1.6-22). OR for prone sleeping was higher in girls, at 30.4 (11-88), than in boys, 10.3 (5.5-19). We found strong combined effects of sleeping position and prenatal risk factors (more than multiplicative). The OR for prone and side sleeping was increased for infants with birth weight <2500 g, at 83 (25-276) and 36.6 (13-107); for preterm infants, at 48.8 (19-128) and 40.5 (14-115); and for intrauterine growth retarded, at 38.8 (14-108) and 9.6 (4.3-22), compared with supine position in infants without these prenatal factors. The combined effect of nonsupine positions and intrauterine growth retarded was highest among 13- to 24-week-old infants. Effects of combined presence of nonsupine sleeping positions and each of the factors of smoking in pregnancy, young maternal age, higher parity, low level of maternal education, and single motherhood were more than additive. Attributable fractions in the population for prone and side sleeping were 18.5% and 26.0%.

CONCLUSIONS

Both prone and side sleeping increased the risk of SIDS. The risk was increased further in low birth weight infants, preterm infants, and infants at the age of 13 to 24 weeks, suggesting that SIDS may be triggered by nonsupine sleeping in infants with prenatal risk factors during a vulnerable period of postnatal development.

The decline in the incidence of SIDS in Scandinavia and its relation to risk-intervention campaigns. Nordic Epidemiological SIDS Study

A prospective case-control study of sudden infant death syndrome (SIDS) in Norway, Denmark and Sweden between September 1, 1992 and August 31, 1995 comprised 244 cases and 869 matched controls. After the introduction of risk-intervention campaigns, the SIDS incidence decreased from 2.3/1000 live births in Norway, 1.6 in Denmark and 1.0 in Sweden to 0.6/1000 or fewer in all the Scandinavian countries in 1995. The decrease paralleled a decline in the prone sleeping position and there was an accompanying parallel fall in total postneonatal mortality in all three countries. Thus, the risk-reducing campaigns for SIDS have been successful not only in Norway and Denmark, starting from relatively high incidences, but also in Sweden, starting from a low incidence. During the study period, a gradual increase was observed for the effects of prone sleeping, smoking and bottle-feeding as risk factors for SIDS.

The epidemic of SIDS in Norway 1967-93: changing effects of risk factors

Time trends on the association of maternal age, birth order, and marital status with the risk of sudden infant death syndrome (SIDS) and non-SIDS deaths in Norway were analysed: 2356 postperinatal SIDS deaths and 4069 postperinatal non-SIDS deaths were ascertained during 1967-93. The SIDS incidence was 1.25 per 1000 in 1967, reached a peak of 2.69 in 1988, and fell to 1.22 in 1990 after the initiation of an intervention programme to avoid prone sleeping. In the entire period, young maternal age, high birth order, and unmarried motherhood were associated with SIDS. The adverse effects of young maternal age and high birth order increased continuously with time. From 1967-71 to 1990-93, the relative risk for maternal age < 20 years v maternal age 25-29 changed from 2.5 (95% confidence interval 2.0 to 3.2) to 7.0 (95% CI 4.2 to 11.9) (p < 0.0001), and for birth order 4+ nu birth order 1 from 3.2 (95% CI 2.5 to 4.2) to 14.4 (95% CI 8.3 to 24.9) (p < 0.0001). Effects on non-SIDS deaths were far weaker and no secular trends were observed. The strong association of young maternal age, high birth order, and marital status in SIDS, but not in non-SIDS, provides evidence that SIDS is an epidemiological entity. The increasing effects of young maternal age and high birth order, which continued after the sudden drop in the SIDS rate in 1990, suggest that further efforts to prevent SIDS should be aimed particularly at identifying causal mechanisms in high risk groups.

Pre- and postnatal medical care and risk of sudden infant death syndrome

The current study investigated whether sufficient attendance at prenatal and postnatal checks affects the risk of sudden infant death syndrome. A case-control study in the Tyrol enrolled 99 infants with sudden infant death syndrome that occurred between 1984 and 1994, and 136 randomly selected control cases. The risk of sudden infant death syndrome was higher in infants whose mothers attended less than five antenatal health checks than in the group with at least five or more visits (OR 5.1; p < 0.01). Babies who received medical help beyond routine health controls had a lower risk than those who did not (OR 0.32; p < 0.001). These differences persisted when social and demographic variables (mother's age at delivery, educational level, marital status, parity and gestational age) were taken into account. Our study identified inadequate antenatal and postnatal care as a risk indicator for sudden infant death syndrome and as a potential target for further educational work. Clinical recommendations should await the results of further evaluations.

Can risk factors for over-heating explain epidemiological features of sudden infant death syndrome?

Sudden infant death syndrome is characterized by a number of epidemiological features that have defied simple explanation. Overheating is believed to play a role in its causation. Overheating can be caused by changes in heat production, changes in insulation of the infant, or changes in the external environmental temperature. Risk factors may influence any of these variables. A model is proposed which links risk factors for overheating to the epidemiological distribution of sudden infant death syndrome. This model might account for the frequently reported association between formula-feeding and sudden infant death syndrome.

Preventing sudden infant deaths--the slow diffusion of an idea

The sudden infant death syndrome (SIDS) is among the leading causes of post-neonatal mortality in industrialised countries. Research has highlighted that many of these deaths are avoidable by adopting a few simple precautions. These include sleeping in the supine position, avoiding exposure to tobacco smoke, breast feeding where possible, and avoiding over heating. The paper traces the development of understanding of the role of sleeping position in the aetiology of SIDS and the diffusion of this knowledge among and within industrialised countries. In retrospect, evidence began to become available in the early 1980s but it was several years before it was acted upon, initially in The Netherlands and subsequently in New Zealand, the United Kingdom and Scandinavia. Several countries have mounted major national preventive campaigns, of various kinds, each of which has been associated with a reduction in deaths from SIDS, but others have not. The reasons for these differences are explored. The evidence for a causal link between sleeping position and SIDS is now very strong and the costs of implementing a policy to change behaviour is small, compared with other health care interventions. This information is now widely available in the international literature. The example of SIDS provides information on the barriers to adoption of knowledge as well as the factors that promote it.

Current concepts and issues in the management of regurgitation of infants: a reappraisal. Management guidelines from a working party

Regurgitation in infants is a common problem. Recent issues, such as the increased risk of sudden infant death in the prone sleeping position, the finding of persisting occult gastro-oesophageal reflux with feed thickeners, and the increasing awareness of the cost-benefit ratio of medications may challenge the currently recommended management approach. A round table was organized to elaborate on the impact of (i) the pro supine sleeping campaigns in relation to sudden infant death and (ii) advancement in medical treatment on therapeutic strategies in regurgitating infants. The participants were opinion leaders from Europe and North America (Belgium, Canada, France, UK, Italy, Switzerland and The Netherlands). The importance of parental reassurance is stressed. As a consequence of the supine sleeping campaigns aiming to decrease the incidence of sudden infant death syndrome, the "prone elevated sleeping position" is no longer advised as a first-line therapeutic approach, although it is still recommended in "complicated reflux". It is emphasized that milk thickeners are an adequate therapeutic tool for regurgitation, but not in reflux disease. According to the literature, the efficacy of (alginate )antacids, although very popular in some countries, is questionable. These recommendations will be of interest to first-line paediatricians, since about 40% of their patients, according to the literature, present because of regurgitation.