Sudden infant death syndrome

Incidence of sudden infant death syndrome in Olmsted County, Minnesota: 1945 through 1992

OBJECTIVE

To apply uniform diagnostic criteria for sudden infant death syndrome (SIDS) for an extended period for comparison of incidence rates from 1945 to 1992 in Olmsted County, Minnesota, to investigate the influence of a person-time or live birth denominator on the estimate of incidence, to calculate the proportionate mortality rate for SIDS over time, and to evaluate the accuracy of death certificates for case ascertainment and the role of interobserver variation in case classification.

DESIGN

We retrospectively reviewed the autopsy results and complete medical records for all infant death from 1945 through 1992 for residents of Olmsted County, Minnesota.

MATERIAL AND METHODS

Cases were identified from a computerized list of all Olmsted County deaths of infants occurring at ages 48 hours to 365 days. All resident cases were categorized as non-SIDS, possible SIDS, SIDS, or incomplete, on the basis of findings from autopsy and clinical history. Incidence rates were calculated for two different SIDS groups and with use of denominators of person-time and live births.

RESULTS

For the study period, 82 cases of SIDS were identified (97% white and 3% Asian). The mean age at death was 12.5 weeks; male infants constituted 59% of cases. No significant trend in seasonal distribution was noted; 73% of deaths occurred between midnight and noon. The incidence rate, defined as SIDS definite and possible deaths per 1,000 resident live births, increased from 0.55 in 1950 through 1953 to 1.28 in 1990 through 1992. The secular trend was best described by a linear model with constant positive slope. Similar trends were observed with other definitions of incidence. During the study period, SIDS as a percentage of total infant deaths dramatically increased, ranging from 2.5 in 1950 through 1953 to 17.9 in 1990 through 1992. The death certificate diagnosis correctly predicted 72% of SIDS cases before 1970 and 100% of cases after 1970.

CONCLUSION

Since 1945, the incidence of SIDS apparently has increased, although diagnostic transfer from other causes of death probably contributes to the observed trend. The comparison of live births versus person-time as denominators showed no significant difference in incidence rates. Interobserver reliability is modest for SIDS cases diagnosed before 1970 and may contribute to the variability in reported SIDS incidence rates.

Epidemiology of sudden infant death syndrome in Japan

An epidemiological survey was carried out to examine the present situation with respect to sudden infant death syndrome (SIDS) in Kanagawa Prefecture. Questionnaires on sudden unexpected death of infants aged < 1 year in 1990-91 were sent to the hospitals and clinics in Kanagawa Prefecture which may take care of such infants. By analysing information from 10,485 replies, 48 out of 73 reported sudden infant deaths were confirmed to be SIDS, although autopsy was not performed in 13 cases (27%). The incidence of SIDS per 1000 live births in Kanagawa Prefecture was 0.29 in 1990 and 0.31 in 1991; and if limited to autopsy cases 0.19 and 0.25, respectively. Sudden infant death syndrome cases in Japan were found to occur more frequently when infants were < 6 months old, at home and sleeping alone, but less in the winter and between midnight and early morning. There was little difference between the numbers in prone and supine sleeping positions at discovery. It was not clear whether SIDS occurred more often to babies sleeping prone than supine, because there were no controls matched with the SIDS cases. In future, continuous epidemiological surveys of SIDS in Japan should be carried out.

SIDS and chaos

Sudden Infant Death Syndrome may exhibit chaotic behavior because it fits common characteristics of chaotic systems including unpredictability, sensitivity to initial conditions, dependence on parameters, and coupling. Chaos theory suggests that preventive efforts should be added to those directed toward a 'cure'.

Caffeine exposure in utero increases the incidence of apnea in adult rats

Caffeine abuse during pregnancy may be a factor in the development of long-term breathing abnormalities. Therefore, the objective of the present study was to monitor adult breathing patterns after in utero exposure to caffeine. This was done by isolating episodes of apnea of more than 6-s duration from the breathing data as obtained by the Cotwatch breathing monitors adapted for rat use. The breathing record obtained over 6 consecutive days was expressed as daily weighted apnea-hypopnea density (WAHD) values. It was shown that administration of caffeine in moderate (30 mg/kg daily) or high (60 mg/kg daily) doses throughout gestation resulted in a significant dose-dependent increase in the WAHD value. The experimental offspring were significantly growth retarded in utero and their subsequent growth rates were also affected. The caffeine-exposed pups grew more slowly with growth plateauing at the same age, resulting in smaller adults. A link was suggested between infants with apnea of prematurity, when occurring after the first week, and an increased risk for later apnea and sudden infant death syndrome.

Caffeine-mediated effects on reproductive health over two generations in rats

The present study was designed to investigate the mechanism(s) underlying previously observed birth weight differences found in the first litter of the second (F2) generation bred from caffeine-exposed F1 females. The effect of exposure to caffeine in utero on subsequent sexual receptivity, fertility, gestation length, parturition, nesting activity, maternal behaviour, and reproductive senescence in the F1 mothers, and the viability of the F2 offspring was investigated. This information was collected by breeding control or caffeine exposed females for 8 consecutive litters. It was demonstrated that exposure to caffeine did not affect the sexual receptivity, fertility, gestation length, or maternal behaviour of the F1 females, but parturition was prolonged and the viability of the F2 generation was seriously jeopardized. Many F2 pups were born significantly larger than their control counterparts and a significant proportion of litters (after the first two litters) were wholly stillborn. It was concluded that a changed genetic program, mediated via the F2 fetus, delayed the normal progression of parturition. This, in turn, compromised the F1 mothers and caused increased mortality of their offspring. The severity of the outcome was dose dependent.