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

Accepted 18 March 1997
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+ v 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.

     

Risk factors for unexplained antepartum fetal death in Norway 1967-1998

OBJECTIVE: To relate unexplained antepartum fetal death with maternal and fetal characteristics in order to identify risk factors. DESIGN: Population-based study based on records of 1,676,160 singleton births with gestational age > or =28 weeks. Unexplained antepartum fetal death was defined as fetal death before labour without known fetal, placental, or maternal pathology. RESULTS: Although unexplained fetal mortality in general declined from 2.4 per 1000 births in 1967-1976 to 1.6 in 1977-1998, the proportion among all fetal deaths increased from 30% to 43% during the same period of observation. Unexplained fetal death occurred later in gestation than explained. From 39 weeks of gestation, the risk increased progressively to 50/10,000 in women aged > or =35 years and <10/10,000 in women <25 years. In birth order > or =5, the risk was particularly high after 39 weeks of gestation. For birth weight percentile 2.5-9.9 and > or =97.5, unexplained fetal death was four and three times more likely to occur, respectively. We found an additive effect of maternal age and birth weight percentile 2.5-9.9. Women with less than 10 years education had higher risk than women with 13 years or more (OR=1.6). Weaker associations were observed with female gender, unmarried mothers, and winter season. CONCLUSIONS: Unexplained antepartum fetal death occurred later in gestation than explained and was associated with high maternal age, multiparity, low education, and moderately low and high birth weight percentile. The increased risk in post-term pregnancies and the additive effect of maternal age and birth weight percentile 2.5-9.9 suggests that older women would benefit from monitoring of fetal growth.     

Modifiable risk factors for SIDS in Germany: results of GeSID

Background: The incidence of sudden infant death syndrome (SIDS) has been falling in Germany over the last decade. However, little is known about the prevalence and the importance of well-known risk factors in Germany since a local prevention campaign in 1992. Design: A 3-y, population-based, case-control study was conducted in half of Germany, consisting of 333 cases. All sudden and unexpected deaths in infancy, if they fitted the inclusion criteria, were included in the study. Parental interview was carried out soon after the death, and three living control infants, matched for age, gender, region and sleep time, were recruited. Results: The prevalence of placing infants prone to sleep was only 4% in the control group, but this was associated with a markedly increased risk of SIDS (adjusted odds ration, aOR=6.08). Other modifiable risk factors for SIDS were: maternal smoking during pregnancy, breastfeeding for less than 2 wk (aOR=1.71) and co-sleeping (aOR=2.71), while using a pacifier during the last sleep reduced the risk (aOR=0.39).

Conclusions: Previously recognized risk factors for SIDS also occur in Germany. Despite knowledge about the major modifiable risk factors for SIDS, these factors are still present in Germany. To reduce the incidence of SIDS in Germany, a continued effort is needed to inform all parents about preventable risk factors for SIDS.     

SIDS risk factors and factors associated with prone sleeping in Sweden

Objective

To compare the current prevalence of risk factors for sudden infant death syndrome (SIDS) in Sweden with a decade earlier, and assess factors associated with prone sleeping.

Methods

The results of a cohort study (Infants of Western Sweden) and a population based case‐control study (Nordic Epidemiological SIDS Study) were examined. Subjects were 5600 healthy 6 month old infants born in 2003 in the Western Sweden region and 430 healthy Swedish infants born between 1991 and 1995.

Results

Prone sleeping decreased from 31.8% to 5.6% and supine sleeping increased from 35.3% to 47.3%. Side or side/supine sleeping increased from 25.2% to 43.8%. Maternal smoking during pregnancy decreased from 23.5% to 9.5%. The risk for prone sleeping increased if the mother was unemployed (OR 2.4, 95% CI 1.5 to 4.0), if she was a heavy smoker in the third trimester (OR 44.1, 95% CI 1.6 to 1199.6), and if the child was irritable (OR 2.5, 95% CI 1.3 to 5.1), shared a bedroom with siblings (OR 2.6, 95% CI 1.0 to 6.6), or never used a dummy (OR 3.2, 95% CI 1.9 to 5.4).

Conclusions

Parents have complied with advice to prevent SIDS given at infant welfare centres for the last 10 years. A change in the preferred sleeping position from side variants to exclusively supine, and reducing the number of pregnant women smoking may be beneficial. Use of a prone sleeping position was associated with maternal employment status, maternal smoking, temperament of the child, dummy use, and sharing a bedroom with siblings.     

SIDS risk factors and factors associated with prone sleeping in Sweden.

OBJECTIVE: To compare the current prevalence of risk factors for sudden infant death syndrome (SIDS) in Sweden with a decade earlier, and assess factors associated with prone sleeping. METHODS: The results of a cohort study (Infants of Western Sweden) and a population based case-control study (Nordic Epidemiological SIDS Study) were examined. Subjects were 5600 healthy 6 month old infants born in 2003 in the Western Sweden region and 430 healthy Swedish infants born between 1991 and 1995. RESULTS: Prone sleeping decreased from 31.8% to 5.6% and supine sleeping increased from 35.3% to 47.3%. Side or side/supine sleeping increased from 25.2% to 43.8%. Maternal smoking during pregnancy decreased from 23.5% to 9.5%. The risk for prone sleeping increased if the mother was unemployed (OR 2.4, 95% CI 1.5 to 4.0), if she was a heavy smoker in the third trimester (OR 44.1, 95% CI 1.6 to 1199.6), and if the child was irritable (OR 2.5, 95% CI 1.3 to 5.1), shared a bedroom with siblings (OR 2.6, 95% CI 1.0 to 6.6), or never used a dummy (OR 3.2, 95% CI 1.9 to 5.4). CONCLUSIONS: Parents have complied with advice to prevent SIDS given at infant welfare centres for the last 10 years. A change in the preferred sleeping position from side variants to exclusively supine, and reducing the number of pregnant women smoking may be beneficial. Use of a prone sleeping position was associated with maternal employment status, maternal smoking, temperament of the child, dummy use, and sharing a bedroom with siblings.     

Mothers' knowledge of the risk factors and anxiety about SIDS

Objective : To assess the impact on mothers' knowledge and anxiety of the 1991-92 health promotion campaign on Sudden Infant Death Syndrome (SIDS) risk factors.
Methodology : A telephone survey of a population based sample of 339 mothers in Victoria, Australia, conducted 1992-94.
Results : Recall by mothers of the risk factors for SIDS was as follows: not breast-feeding. 15%; smoking, 46%; overheating, 48%; and prone sleeping, 84%. Recall rate increased as the campaign progressed. Receiving the campaign pamphlet was associated with an increased recall of all risk factors. Discussion of the pamphlet with a health professional was rare (9%). One-third of all mothers reported being very worried about cot death when caring for their babies. Self-reported worry was significantly more common among mothers whose babies were born at the time of the campaign introduction.
Conclusions : The campaign pamphlets were effective in increasing knowledge of the risk factors. The limited discussion with health professionals suggests that future campaigns need increased professional involvement to address problems, including anxiety among new mothers.     

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

OBJECTIVE--To investigate, in a population based national study, the association between sleeping position of infants and the occurrence of sudden infant death syndrome (SIDS). DESIGN--A retrospective survey and registry based ecological study. A questionnaire based surveillance of sleeping position was obtained in a random sample (n = 34,799) and surveillance of SIDS was based on all infants born in Norway 1967-91, surviving the perinatal period. Variables studied from the questionnaire were usual sleeping position (placed), breast feeding at 3 months, and maternal smoking in pregnancy, and from the Medical Birth Registry maternal age, birth order, and birth weight. RESULTS--Proportion of infants sleeping prone increased from 1970 (7.4%) to 1989 (49.1%) and dropped in 1990 (26.8%) and 1991 (28.3%). Occurrence of SIDS increased from 1970 (1.1/1000) to 1989 (2.0) before dropping in 1990 and 1991 (1.1). IMPLICATION AND RELEVANCE OF RESULTS--A cause effect relationship between prone sleeping and SIDS as suggested in previous studies is supported by the present; and so far only, national study of infants' sleeping position.     

The silent epidemic of falls from buildings: analysis of risk factors

This study wanted to search for potential risk factors associated with falls from windows and balconies in order to eventually improve prevention. All children under the age of 16 years suffering from head injuries/multiple trauma due to falls from windows or balconies treated over the last 7 years at the intensive care unit (ICU) of the University Children’s Hospital Zürich were analysed retrospectively (group A). Fifty patients out of all children suffering from head injuries/multiple trauma due to other types of accidents in the same period were selected at random as controls (group B). Out of a total of 241 children with head injury and/or multiple trauma, 31 (13%) fell out of a building. Twenty-seven of these victims (87%) fell from the third floor or lower. Twenty-one of the falls (68%) occurred at home. Fifteen children (49%) climbed on a piece of furniture before falling. In almost 20% of the accidents dangerous balcony or house constructions led to the fall. Parents did not witness the fall, except for three cases (10%) with direct parental involvement (one mother jumped out with her child, two mothers threw their child out of the window). Two children (6%) attempted suicide. Children aged 0–5 years were predominantly represented (84%), and all six children who died were in this age group. There were significantly more patients with foreign nationalities and lower socio-professional categories in group A than in group B. In both groups, the accidents concerned the youngest child of the family in approximately 50% and happened mostly during summer evenings. There were no significant differences in injured systems and in injury severity between the two groups. This study identified young age, an immigrant family setting, low socio-professional category of the parents, dangerous house constructions, inappropriate furniture placement, and summertime evenings as risk factors for serious building falls in children. This information may foster focused prevention.     

An 8 year study of risk factors for SIDS: bed-sharing versus non-bed-sharing

Background

It is unclear if it is safe for babies to bed share with adults. In Ireland 49% of sudden infant death syndrome (SIDS) cases occur when the infant is bed‐sharing with an adult.

Objective

To evaluate the effect of bed‐sharing during the last sleep period on risk factors for SIDS in Irish infants.

Design

An 8 year (1994–2001) population based case control study of 287 SIDS cases and 831 controls matched for date, place of birth, and sleep period. Odds ratios and 95% confidence intervals were calculated by conditional logistic regression.

Results

The risk associated with bed‐sharing was three times greater for infants with low birth weight for gestation (UOR 16.28 v 4.90) and increased fourfold if the combined tog value of clothing and bedding was ⩾10 (UOR 9.68 v 2.34). The unadjusted odds ratio for bed‐sharing was 13.87 (95% CI 9.58 to 20.09) for infants whose mothers smoked and 2.09 (95% CI 0.98 to 4.39) for non‐smokers. Age of death for bed‐sharing and sofa‐sharing infants (12.8 and 8.3 weeks, respectively) was less than for infants not sharing a sleep surface (21.0 weeks, p<0.001) and fewer bed‐sharing cases were found prone (5% v 32%; p = 0.001).

Conclusion

Risk factors for SIDS vary according to the infant''s sleeping environment. The increased risk associated with maternal smoking, high tog value of clothing and bedding, and low z scores of weight for gestation at birth is augmented further by bed‐sharing. These factors should be taken into account when considering sleeping arrangements for young infants.     

Case-control study of current validity of previously described risk factors for SIDS in The Netherlands

This study aimed to assess whether previously established risk factors for sudden infant death syndrome (SIDS) are still valid now that the incidence in the Netherlands has dropped to 0.26 per 1000 liveborn infants. A distinction was made between immutable and mutable risk factors. This case-control study (part of the European Concerted Action on SIDS) comprised 73 SIDS cases and 146 controls and lasted from March 1995 to September 1996. Adjustments were made for sleeping position and bedding factors by treating them as covariables. Apart from these factors, well known risk factors that remain of importance in the Netherlands are: male sex, young maternal age, twins, and low socioeconomic status. These factors are largely immutable. Other well known risk factors which might reflect attitudes to child care and could possibly be mutable are: smoking, alcohol consumption by the mother, bottle feeding, and change of babycare routine. Intervention strategies should focus on early signalling, thereby assisting parents in changing these unfavourable parenting attitudes. Information on optimal child care and extra support by public health nurses specifically aimed at families at risk could help to decrease further the incidence of SIDS in the Netherlands.     

An 8 year study of risk factors for SIDS: bed-sharing versus non-bed-sharing.

BACKGROUND: It is unclear if it is safe for babies to bed share with adults. In Ireland 49% of sudden infant death syndrome (SIDS) cases occur when the infant is bed-sharing with an adult. OBJECTIVE: To evaluate the effect of bed-sharing during the last sleep period on risk factors for SIDS in Irish infants. DESIGN: An 8 year (1994-2001) population based case control study of 287 SIDS cases and 831 controls matched for date, place of birth, and sleep period. Odds ratios and 95% confidence intervals were calculated by conditional logistic regression. RESULTS: The risk associated with bed-sharing was three times greater for infants with low birth weight for gestation (UOR 16.28 v 4.90) and increased fourfold if the combined tog value of clothing and bedding was > or =10 (UOR 9.68 v 2.34). The unadjusted odds ratio for bed-sharing was 13.87 (95% CI 9.58 to 20.09) for infants whose mothers smoked and 2.09 (95% CI 0.98 to 4.39) for non-smokers. Age of death for bed-sharing and sofa-sharing infants (12.8 and 8.3 weeks, respectively) was less than for infants not sharing a sleep surface (21.0 weeks, p<0.001) and fewer bed-sharing cases were found prone (5% v 32%; p = 0.001). CONCLUSION: Risk factors for SIDS vary according to the infant's sleeping environment. The increased risk associated with maternal smoking, high tog value of clothing and bedding, and low z scores of weight for gestation at birth is augmented further by bed-sharing. These factors should be taken into account when considering sleeping arrangements for young infants.     

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

OBJECTIVE--To investigate, in a population based national study, the association between sleeping position of infants and the occurrence of sudden infant death syndrome (SIDS). DESIGN--A retrospective survey and registry based ecological study. A questionnaire based surveillance of sleeping position was obtained in a random sample (n = 34,799) and surveillance of SIDS was based on all infants born in Norway 1967-91, surviving the perinatal period. Variables studied from the questionnaire were usual sleeping position (placed), breast feeding at 3 months, and maternal smoking in pregnancy, and from the Medical Birth Registry maternal age, birth order, and birth weight. RESULTS--Proportion of infants sleeping prone increased from 1970 (7.4%) to 1989 (49.1%) and dropped in 1990 (26.8%) and 1991 (28.3%). Occurrence of SIDS increased from 1970 (1.1/1000) to 1989 (2.0) before dropping in 1990 and 1991 (1.1). IMPLICATION AND RELEVANCE OF RESULTS--A cause effect relationship between prone sleeping and SIDS as suggested in previous studies is supported by the present; and so far only, national study of infants'' sleeping position.     

A multivariate "time based" analysis of SIDS risk factors

Aims: To investigate the influence of analytical design on the variability of published results in studies of sudden infant death syndrome (SIDS). Methods: The results of a prospective case-control study, of 203 cases of SIDS, and 622 control infants are presented. All variables significant on univariate analysis were included in a multivariate model analysed in nine stages, starting with sociodemographic variables, then sequentially and cumulatively adding variables relating to pregnancy history, current pregnancy, birth, the interval from birth to the week prior to death, the last week, the last 48 hours, and the last sleep period. A ninth stage was created by adding placed to sleep prone for the last sleep period. Results: As additional variables are added, previously published SIDS risk factors emerged such as social deprivation, young maternal age, ?3 previous live births, maternal smoking and drinking, urinary tract infection in pregnancy, reduced birth weight, and the infant having an illness, regurgitation, being sweaty, or a history of crying/colic in the interval from birth to the week before death, with co-sleeping and the lack of regular soother use important in the last sleep period. As the model progressed through stages 1–9, many significant variables became non-significant (social deprivation, young maternal age, maternal smoking and drinking) and in stage 9 the addition of placed to sleep prone for the last sleep period caused ?3 previous live births and a reduced birth weight to become significant. Conclusion: The variables found to be significant in a case-control study, depend on what is included in a multivariate model.     

Case-control study of current validity of previously described risk factors for SIDS in The Netherlands.

This study aimed to assess whether previously established risk factors for sudden infant death syndrome (SIDS) are still valid now that the incidence in the Netherlands has dropped to 0.26 per 1000 liveborn infants. A distinction was made between immutable and mutable risk factors. This case-control study (part of the European Concerted Action on SIDS) comprised 73 SIDS cases and 146 controls and lasted from March 1995 to September 1996. Adjustments were made for sleeping position and bedding factors by treating them as covariables. Apart from these factors, well known risk factors that remain of importance in the Netherlands are: male sex, young maternal age, twins, and low socioeconomic status. These factors are largely immutable. Other well known risk factors which might reflect attitudes to child care and could possibly be mutable are: smoking, alcohol consumption by the mother, bottle feeding, and change of babycare routine. Intervention strategies should focus on early signalling, thereby assisting parents in changing these unfavourable parenting attitudes. Information on optimal child care and extra support by public health nurses specifically aimed at families at risk could help to decrease further the incidence of SIDS in the Netherlands.     

A multivariate "time based" analysis of SIDS risk factors.

AIMS: To investigate the influence of analytical design on the variability of published results in studies of sudden infant death syndrome (SIDS). METHODS: The results of a prospective case-control study, of 203 cases of SIDS, and 622 control infants are presented. All variables significant on univariate analysis were included in a multivariate model analysed in nine stages, starting with sociodemographic variables, then sequentially and cumulatively adding variables relating to pregnancy history, current pregnancy, birth, the interval from birth to the week prior to death, the last week, the last 48 hours, and the last sleep period. A ninth stage was created by adding placed to sleep prone for the last sleep period. RESULTS: As additional variables are added, previously published SIDS risk factors emerged such as social deprivation, young maternal age, > or =3 previous live births, maternal smoking and drinking, urinary tract infection in pregnancy, reduced birth weight, and the infant having an illness, regurgitation, being sweaty, or a history of crying/colic in the interval from birth to the week before death, with co-sleeping and the lack of regular soother use important in the last sleep period. As the model progressed through stages 1-9, many significant variables became non-significant (social deprivation, young maternal age, maternal smoking and drinking) and in stage 9 the addition of placed to sleep prone for the last sleep period caused > or =3 previous live births and a reduced birth weight to become significant. CONCLUSION: The variables found to be significant in a case-control study, depend on what is included in a multivariate model.     

Maternal and perinatal risk factors for SIDS: a novel analysis utilizing pregnancy outcome data

A number of maternal and perinatal factors to increase an infant’s risk of sudden infant death syndrome (SIDS) have been found in past investigations. We analysed data for potential SIDS risk factors including the presence of complications or conditions considered as detrimental to the infant’s or mother’s health. The data for 118 SIDS cases and 227 matched controls were obtained from a state pregnancy outcome unit. SIDS was found to be significantly more common in cases where the infant’s mother was not in a relationship (i.e. divorced, separated or never married) (p?=?0.005), if the infant was not the first born (p?=?0.0001) and when the mother resided in a socioeconomically disadvantaged area (p?=?0.03). Conclusion: Overall, this SIDS cohort appears to display classical SIDS associations, and our findings are consistent with those from other regions. This novel epidemiological tool opens the way for a national Australia-wide study using pregnancy outcome data collected by the individual states and could be helpful in assessing maternal and fetal risk factors for other paediatric medical conditions.