Smoking and the Risk for SIDS

Smoking is among the more sensitive issues to discuss as a risk factor for SIDS. It is a sensitive issue since this article will be viewed by smokers as well as nonsmokers. Some of them will already have lost a child due to SIDS and are concerned about future pregnancies and others will be reading while anticipating their first delivery or pregnancy. In addition, smoking is a habit that is gradually acquired and not so easy to discard, even if there are compelling reasons to do so.

Maternal smoking has long been linked with increased SIDS risk. The increased risk correlated with how much the mother smokes. Several studies have demonstrated that passive tobacco smoke also significantly increases the risk for SIDS. The risk for SIDS is increased, in normal birth weight infants, about two-fold with passive smoke exposure and about three-fold when the mother smokes both during the pregnancy and the baby continues to be exposed to tobacco smoke after he/she is born. Kahn and colleagues have shown that infants born to mothers who smoked during pregnancy had lower birth weight, and significantly more episodes of obstructive apnea and excessive sweating (the infants were tested at about three months of life and compared to infants of nonsmoking mothers). Recent epidemiological studies from New Zealand, Tasmania, and England have reported the prospective results of supine (back) sleep position and significant reduction of SIDS risk. The greatest reduction of risk, however, was found when the infant was placed supine (back) during sleep, was breast fed, and was not exposed to maternal smoking during pregnancy or to passive tobacco smoke following birth.

Recent studies have provided more details on the epidemiology and on possible physiologic mechanisms underlying the association between smoking and SIDS. Kinney et al. have documented significant changes in nicotine-binding sites in the brainstem areas involved with arousal, heart and breathing functions, sleep, and body movement control, during the last half of pregnancy. Thus, mid to late pregnancy may be a particularly vulnerable period for the fetus exposed to the nicotine in maternal tobacco smoke. We do not know exactly how smoking affects the infant during the pregnancy, however, we have several leads which suggest that the effect may influence development of the nervous system.

It is important to keep in mind that the majority of infants who had SIDS did not have mothers who smoked. As with many SIDS risk factors, the absence of smoking is not protection or a prevention. However, if you smoke and are planning another pregnancy, the first step is to make the decision to at the very least, reduce the number of cigarettes you smoke each day and to ask for a referral to a smoking cessation class. Nonsmokers, the author included, have no personal experience about what it means, psychologically or physically, to face stopping. Nevertheless, we have good reason to believe and to strongly recommend that pregnant women not smoke. The best information to date supports the advice that your baby sleep on his/her back for at least the first six months of life unless that is considered medically contraindicated by your doctor, to breast feed if possible, avoid smoking during your pregnancy, and avoid exposing your infant to passive tobacco smoke following birth.

Article by: Ronald Ariagno, M.D., Stanford Medical School, Department of Pediatrics; Chairperson, SIDS Northern California Regional Council; Member, California SIDS Advisory Council.

Reprinted with permission from Horizons, Vol. 1, No. 3, Fall/Winter 1994, California SIDS Program