Can Risk Factor Intervention Lower SIDS Risk?

Patrick Carolan, MD
Medical Director, MN SID Center

This article is reprinted with permission from the Minnesota Sudden Infant Death Center Newsletter, Volume 13, Number 2, June 1993. The center's address is Minnesota Sudden Iinfant Death Center, Minneapolis Children's Medical Center, 2525 Chicago Ave. S., Minneapolis, MN 55404.

There have been a number of articles in both the medical as well as the lay literature that have addressed the issues of SIDS risk factors, their relationship to SIDS and potential strategies to reduce SIDS risk. Infant sleep position has been the most widely publicized example within the last year. Other factors that have been cited include: infant bedding and bundling, cigarette smoke exposure, breast feeding, regular prenatal and infant medical care, seasonality and pregnancy planning, among others. I thought it would be helpful to explore what is known about these factors as they relate to "risk for SIDS" and whether it is reasonable to advise families that "risk for SIDS" can be modified by intervening on these factors.

The relationship between infant sleep position and SIDS continues to be the subject of considerable controversy. Researchers in Great Britain, Australia, New Zealand and Europe continue to support the theory that the prone (tummy down) sleep position is a contributing factor in SIDS. They continue to advocate the supine (back) sleep position as the preferred position for sleep. Physicians and researchers in me U.S., for the most part, continue to take a more cautious approach to this issue. There has been little additional published scientific data on this issue since the American Academy of Pediatrics published their statement in April 1992. We are all looking forward to the results of studies that are currently underway that are related to the issue of infant sleep position. Several papers related to infant sleep position will be presented at the proceedings of the Society for Pediatric Research / Ambulatory Pediatric Association to be held in May in Washington D.C. I will update you on these results as they are available. We are progressing on our own study of normal infant care practice in Minnesota. This is part of a multicenter, international survey which we feel will offer some insight on infant sleep position among other issues.

Another consideration related to the infant sleep environment is whether certain types of bedding surfaces are unsafe for infants. This issue was raised following several infant deaths occurring on waterbed or "bean bag" like surfaces. Researchers evaluating these deaths suggested that deep pockets may be created on these surfaces by an infant's head. In the face down position, this may force the infant to rebreathe its own exhaled carbon dioxide or to breathe oxygen-poor air. For this reason, researchers have advised against placing an infant for sleep on an excessively padded surface favoring instead a firm surface, like a standard infant mattress, with tight fitting sheets. While these recommendations seem reasonable, parents must be aware that there is still a great deal we need to understand about an infant's ability to overcome the potential hazards posed by these or other similar surfaces.

The potential hazards of cigarette smoke exposure and risk for SIDS have been documented in a number of studies. This association was first noted in studies in the 1970's, confirmed in the large NICHD Cooperative Epidemiologic Survey of the early 1980's and reconfirmed in numerous studies since. Our Center's own epidemiologic survey of 1976-1990 associated an increased rate of SIDS by race with a history of maternal cigarette smoking. A recent study (Schoendorf 1992) suggests that both maternal smoking during pregnancy as well as passive cigarette smoke exposure following birth are associated with an increased risk of SIDS. These authors rightly conclude that this information considered together strongly supports efforts to encourage smoking cessation among pregnant women and families with children.

Breast feeding and regular medical care have been cited as strategies to reduce risk for SIDS. Since it has been observed that breast-fed infants have fewer bouts of minor respiratory or gastrointestinal infection, it has been suggested that risk for SIDS might be altered by reducing or eliminating these "stress events" for potentially vulnerable infants. In a similar manner, regular medical care both during pregnancy for mothers and following birth for infants is felt by some to be a positive intervention to lower SIDS risk presumably because of the opportunity to identify health-related problems in their earliest stages. While it is easy to support breast feeding and regular medical care from the public health standpoint, the research evaluating issues is exceedingly complex because of the many variables that are mixed together. It makes separating out the effect of a single factor very difficult. Hopefully, improved research design will enable us to develop better answers to these important questions.

Finally, the timing of pregnancy has been cited as another intervention to lower SIDS risk. Because SIDS incidence peaks during the winter months (MMWR 1990), it has been suggested that infants born in the spring or early summer would pass from the vulnerable period (2 to 4 months of age) prior to the onset of the winter season. Although there is some logical merit to this theory, there is currently no research to support this claim. Perhaps future studies will clarify whether pregnancy planning can effectively lower SIDS risk.

Has attention to infant sleep position, the sleep environment, smoking cessation, breast feeding, regular medical care or pregnancy planning resulted in the reduction in SIDS incidence reported by many centers? As you can see, there are many variables involved in this analysis. In time, we may identify some environmental factors in our search for the cause or causes of SIDS. However, we must keep in mind that for families that have lost infants to SIDS, most of the "risk factors" discussed in various studies simply do not apply. Researchers continue to evaluate the relationship of "risk factor" to SIDS with the hope that this analysis will lead to potential clues to causation (Krongrad 1991, Hass 1993). It is out hope that research will be able to provide better answers for all families in the very near future.

References
Southall DP, Samuels MP. Reducing risks in the sudden infant death syndrome. British Medical Journal 1992. 304: 265 6 Jones K, Noyes J. Practical methods for reducing the risk of sudden death. Health Visitor 1991. 64: 113-4 Schoendorf KC et al. Relationship of SIDS to maternal smoking during and after pregnancy. Pediatrics 1992. 90: 205 8 CDC. Seasonality in SIDS - United States, 1980 - 87. Morbidity and Mortality Weekly Reports 1990. 39 891-5 Krongrad E. Infants at high risk for SIDS. Have they been identified? Pediatrics 1991. 88: 1274-8 Hass JE., et al. Relationship between epidemiologic risk factors and clinicopathologic findings in SIDS. Pediatrics 1993. 91:106-12

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