Discriminatory risk factors in post-neonatal sudden unexplained death

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.

Ethnic differences in the incidence of the sudden infant death syndrome (SIDS) in Victoria, Australia 1985-1989

In order to describe ethnic differences in the incidence of the sudden infant death syndrome (SIDS) records of all livebirths in the State of Victoria, Australia, 1985-1989, excluding those who died in the first month of life, were linked to death certificates. Cases were defined as infants dying with a diagnosis of SIDS between 1 month and 1 year of age (n = 601) from the cohort of 308,052 neonatal survivors. Ethnicity was defined by the mother's country of birth. The SIDS incidence was 2.04/1000 in infants of Australian-born mothers. The relative risk of SIDS was 0.28 (95% confidence interval (CI) 0.15, 0.55) in infants whose mothers had been born in Southern Europe and 0.48 (95% CI 0.29, 0.78) in infants whose mothers had been born in Asia. SIDS in infants of Australian-born mothers was associated with low maternal age, high parity, marital status other than married, male sex, multiple birth, low birthweight and preterm birth. After adjustment for those factors in a case-control analysis using a logistic regression model the adjusted odds ratio for SIDS was 0.34 (95% CI 0.17, 0.69) comparing infants whose mothers were born in Southern Europe with infants of Australian-born mothers, and 0.60 (95% CI 0.35, 1.04) for infants whose mothers were born in Asia, compared with infants of the Australian-born. Thus there are substantial ethnic differences in SIDS which are not explained by the classic social and perinatal risk factors.

Lead and sudden infant death. Investigations on blood samples of SID babies

To investigate a potential relationship between an elevated lead burden and sudden infant death (SID), the lead concentrations (Pb-B) were determined in 41 blood samples from SID babies and compared with the Pb-B of 5 babies who died traumatically and 77 living control babies. Several factors that may influence the Pb-B were taken into consideration, especially a dependence of the Pb-B on age and social class. Moreover, a post-mortem water shift occurs in the blood. Even taking these factors into consideration the distribution of the Pb-B's of the SID group was found to differ on a highly significant level (greater than 99.9%) from the control group. Five Pb-B's of the SID group were higher than the highest lead concentration found in blood from the control babies. Negative influences of lead on the pre- and postnatal maturation of the brain are discussed in the search for a possible causal connection between an elevated lead burden and the occurrence of SID.

Effects of birth weight and ethnicity on incidence of sudden infant death syndrome

Sudden infant death syndrome occurs with increased frequency in low birth weight infants and in black infants. The degree to which the higher LBW rate among blacks might explain this higher SIDS rate is unknown. To address this question, we analyzed the 1233 SIDS deaths that occurred among 252,376 neonatal survivors in Cook County from 1975 to 1980, using computer-coded matched infant birth and death records. Birth weight and ethnic group were identified. The overall SIDS rates in blacks, Hispanics, and whites were 5.1, 1.2, and 1.3/1000 neonatal survivors, respectively. Within each ethnic group, the SIDS rates increased progressively with decreasing birth weight. Within the less than or equal to 1500 gm birth weight groups, the SIDS rates were 16.4, 3.9, and 5.5/1000 neonatal survivors in blacks, Hispanics, and whites. Using direct standardization, we found that 27% of the SIDS rate disparity between blacks and whites could be explained by the higher LBW rate in blacks (14% vs 6% in whites). The good outcomes in both LBW and SIDS rates for the Hispanic population were unexpected because, like blacks, Hispanics are socioeconomically disadvantaged. Findings for this group suggest that the remaining 73% of the increased SIDS rate in blacks cannot be attributed in a straightforward manner to differences in income or educational attainment.

Family size effects: a review

Larger families are more frequent with early marriage and rapid birth of the first child. In larger families, child rearing becomes more rule ridden, less individualized, with corporal punishment and less investment of resources. Smaller families tend to result in higher IQ, academic achievement, and occupational performance. Large families produce more delinquents and alcoholics. Perinatal morbidity and mortality rates are higher in large families as birth weights decrease. Mothers of large families are at higher risk of several physical diseases. Common methodological errors are indicated and exemplary studies are described.

Sudden unexpected infant death in a French county

We report a study of sudden unexpected infant death (SUID) in a French county (Seine-Maritime) between 1978 and 1981 (rate of 2.71 per 1000 live births). The results agree with those of previous studies concerning sex ratio, seasonal variation, and peak age of death. No relation between gestational age and age of death was found. A comparison with matched living control infants was performed for 136 of the 207 total deaths for whom computerised medical data were available. Significant differences were found between these two groups in gestational age, birthweight, admission to a paediatric ward at birth, and proportion of single mothers. In analysing birthweight and gestational age separately, the birthweights of SUID cases were significantly lower than those of controls, whatever the gestational age. The converse was not true, however: in classifying infants by birthweight, a significant difference between the gestation period of SUID victims and controls was found only for low birthweight infants (less than 2500 g). It is considered that it may be possible to identify infants at particular risk of SUID within the group of babies admitted to hospital at birth for major problems, and a study is currently underway among infants born in Seine-Maritime in 1982.

Sudden infant death in Copenhagen 1956--1971. IV. Infant development

131 cases of the Sudden Infant Death Syndrome (SIDS) among infants born in the Municipality of Copenhagen in 1956-71 were analysed on the basis of data collected prospectively by the infant health visitors. Compared with living controls, the frequency of maturity and the mean birth weight and length were lower among the SIDS infants. After making the SIDS and control groups comparable with respect to birth weight and type of feeding, we found a tendency towards a slower growth rate among the SIDS victims. The SIDS victims started to smile and prattle later than controls, while there was no difference as regards the average age at which the infants became able to hold their heads. It is concluded that the differences are so small and the individual variations so wide that birth weight and length, growth rate, and psychomotor development will not be useful predictors of the SIDS.

The epidemiology of sudden infant death in upstate New York: II: birth characteristics

This study describes the epidemiology of sudden infant death syndrome (SIDS) among infants born during 1974 to upstate New York residents. Birth certificate characteristics for 184 SIDS cases are compared with those of 417 infants dying from other causes in the same age range, 7-365 days. The results confirm the following as infant risk factors: fall or winter birth, low birthweight for gestational age, twin birth, and live birth order three or more. Maternal risk factors include: age under 20, abnormal uterine bleeding during pregnancy, late initiation of prenatal care, less than 12 years of education and single marital status. The increased risk for mothers who first gave birth in their teens and for second-born twins has not been previously reported. The evidence that SIDS babies are small for gestational age, that twins, especially the second born, and babies whose mothers experienced abnormal uterine bleeding during pregnancy are all at increased risk of SIDS suggests that perinatal stress leading to hypoxia is one of the components that determine the risk of SIDS.