Ohio death certificate

ABBBREVIATIONS. SIDS, sudden infant death syndrome; IMR, infant mortality rate; IMRP, Infant Mortality Review Program; SD, standard deviation.

In recent years, clinical and epidemiologic studies of sudden infant death syndrome (SIDS) have provided convincing direct and indirect evidence that explains some deaths that would have been formerly classified as idiopathic. These observations are important for 2 reasons. First, these identified causes offer opportunities for prevention. Second, removal from consideration of cases of recognized causation should reduce blurring of results of research directed at the cause of true idiopathic SIDS. The belief that misclassification of cases continues to dilute SIDS research in the United States is reinforced by Knobel, Chien-Jen, and Liang's 1995 statement: "Suffocation as cause of death is rarely recorded in western countries. The situation in Asia is essentially different. Taiwan and Japan both record suffocation rates that are higher than SIDS rates, and together these two causes of death sum up to values similar to those for SIDS in western countries. We include accidental suffocation diagnoses in SIDS, taking the view that from a western perspective both terms would be `synonymous.'"[1]

These points are exemplified by accumulating evidence that some proportion of sudden unexplained infant deaths classified as SIDS is attributable to infants sleeping in the prone position, with hypothesized mechanisms being airway obstruction, rebreathing, and overheating, often in association with other risk factors.[2-4] As a result, several countries launched campaigns to foster the supine sleeping position for infants with apparent reductions of ~50% in SIDS rates.[2-4] In the United States it is estimated that SIDS rates have dropped [is greater than] 40% since the 1992 American Academy of Pediatrics recommendation to avoid the prone sleep position.[5] However, many SIDS cases are not explained by the prone sleep position; indeed, 1 study from California failed to show any effect of prone position.[6] Other contributing factors have been suggested by some studies, including singly or in combination, parental smoking,[7-12] parental drug or alcohol abuse,[11,13,14] unsafe bedding,[15-17] and infanticide.[18,19] A recent assertion that some SIDS may be caused by congenital cardiac electrical instability (the long-QT syndrome)[20] has been severely challenged.[5] Accidental suffocation by parental overlying with bedsharing has also been suggested as a cause.[11,13,18,21-23] One recent study found that 33% of SIDS deaths occurred while bedsharing whereas only 7% of parents routinely bedshared, an observation not commented on by the authors.[24] Some studies indicate an increased SIDS risk for bedsharing infants, especially when linked to smoking by the parent.[12,25] Other reports do not support this suggestion and indeed some claim that bedsharing protects against SIDS by increasing the number of arousals and reducing the slow-wave sleep.[26-29] However, in its March 2000 statement on sleep environment and sleep position, the American Academy of Pediatrics notes that these behavioral studies do not provide any epidemiologic evidence that bedsharing reduces SIDS risk.[5] Subsequently, 2 case series using data from the Consumer Product Safety Commission have implicated parental overlying as a not infrequent cause of death of young infants,[30,31] and the Academy has reiterated concern about the risk of bedsharing[32]; discussion of this concern has reached the public press.[33,34] One recent study from Britain found an increased risk, which the authors interpreted as being attributable to sofasharing but not to bedsharing.[35]

To assess the role of parental bedsharing in SIDS-like deaths, we examined the hypothesis that, compared with other SIDS cases, the age distribution of deaths associated with bedsharing should be lower in younger, less vigorous infants, particularly if the bedsharing parent was obese, possibly caused by overlying.

PATIENTS AND METHODS

Patients

Eighty-four cases classified as SIDS were accrued serially from October 1, 1992, through January 30, 1996. All SIDS deaths that occurred during that time, and for which the review process was complete, were included. All unexplained infant deaths in this county are autopsied by the coroner, a board certified forensic pathologist. All deaths in this report met standard clinical and pathologic criteria for SIDS and were so designated by the coroner on the death certificate.

Methods

Cleveland, Ohio (population 506 000) has approximately 10 000 resident births annually, and in recent years an infant mortality rate (IMR) twice the national rate. In 1994, Cleveland's IMR was 16.1 per 1000 live births,[36] compared with the US rate of 8.0,[37] and the incidence of SIDS was ~2.6, compared with the national rate of 1.0. In 1991, the City of Cleveland received a 5-year federal award to reduce its infant mortality rate and that of a small contiguous community with high infant mortality through comprehensive outreach and educational efforts for mothers pre- and postnatally and their infants. As an evaluation component of these efforts the Infant Mortality Review Program (IMRP), based at Case Western Reserve University, conducted in-depth reviews of all infant deaths that occurred in Cleveland and adjacent Warrensville Heights with approximately 10 000 and 260 annual births respectively. The purposes of this review process were to define as precisely as possible the causes of infant deaths and contributing factors, to assess the potential preventability of each death, and to recommend appropriate interventions. The process, described in detail elsewhere,[38] included exhaustive case finding to capture all infant deaths. Each death was evaluated by extensive examination of all pertinent maternal and infant medical records (prenatal, delivery, well-child care, and emergency department), vital statistics (birth and death certificates), social service records, autopsy reports, emergency medical services reports, and fire and police records. The data were collected in a standard manner by trained, experienced research nurses. Parent interviews were not conducted and there was no standard death scene investigation at the time of the study. The study was approved by the University's Institutional Review Board for Human Investigation and the boards of involved hospitals.

The determination of bedsharing status was based on complete review of all records of the case. Any case for which emergency medical service, emergency department, or other records reported that the infant was sleeping with 1 or both parents at the time of death was classified as bedsharing. Any piece of furniture (bed, couch, sofa, or other) on which the parent and infant were sleeping was considered to be a bed for this analysis. Information on sleep position (prone or supine) was reported in fewer than one third of the cases and was therefore not analyzed. Maternal pregravid weights (the only consistently available measurement) were ascertained from records of prenatal care visits for 76 (91%) of the cases and for 6 from birth certificates; 2 were not recorded. Weights were used in analyses as both continuous and dichotomous variables. For those tests requiring a dichotomous variable, 79.5 kg (175 lbs) was arbitrarily selected as the cutoff point before initiation of the analysis. The infant's age at death was computed from the dates of birth and death. Generally, smoking, alcohol use, and illicit drug use were ascertained as self-reports in medical records. In some instances, but not uniformly, drug use was based on urine toxicology screening. Substance (drug and/or alcohol) use was treated as a dichotomous variable.

Study Design

The infant mortality review was originally designed as a descriptive case series and not as an analytic (causative) epidemiologic study. In the course of the review process, an impression developed that cases reported as SIDS were frequently associated with bedsharing with an obese parent. Accordingly, factors surrounding these 84 deaths ascribed to SIDS were compared retrospectively for 30 bedsharing and 54 nonbedsharing infants. This investigation, therefore, can be described as a case-comparison study.[17]

Statistics

The data were analyzed using the Student's t test, [chi square], Fisher's exact test, Kruskal-Wallis nonparametric 1-way analysis of variance, and the life-table survival method with a Kaplan-Meier log rank test of significance. All tests are reported with 2-tailed probabilities. All analyses were performed using SPSS/PC+.

RESULTS