The New Zealand experience: how smoking affects SIDS rates - Special Issue

New Zealand is a small country--the size of England--with a population of just over four million, of which 15 percent are indigenous Maori. In the 1980s we had the unenviable reputation of having one of the highest rates of infant death in the Western world. The majority of the excess of deaths (compared to other countries)were recorded as being due infant death syndrome (SIDS). (1)

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To find out what we were going wrong, a research group from different parts of the country, including most of the authors of this article, carried out the New Zealand National SIDS Study (1987-1990), which compared infant care practices of parents of 465 babies who died of SIDs with parents of 1,800 who did not. Our questions were deliberately designed to focus on parental actions that were relatively common and that also could be changed. Among other results, (2-20) we found that bedsharing was a risk, but sharing a room (not a bed) was protective. To our surprise, the use of a dummy (pacifier) was a protective factor.

Most important was strong evidence that babies sleeping on their fronts or sides were at much higher risk of dying than those placed on their backs. With supporting evidence coming out of the Netherlands at the same time, we launched a national campaign telling parents that babies should be put to sleep on their backs, that smoking increased the risk of sudden death, and that breastfeeding decreased this risk. The campaign had the effect of halving the numbers of SIDS deaths in New Zealand within a year. Subsequently we discovered that almost all the decreased risk could be attributed to the change in sleep position. (21)

The number of deaths occurring among Maori babies, already at higher risk than the rest of New Zealand babies, did not decline to the same extent, even though the change in sleep position occurred as much in this group. Among the Maori, it is a strong traditional cultural practice for families to share one bed, often throughout childhood. Indeed, in some Pacific Island cultures, not to share a bed with a baby is considered tantamount to child abuse; the thinking is, "Why should parents enjoy the warmth and comfort of sleeping in the same bed, while a newborn baby, used to sleeping inside its mother, is cast out to sleep alone?"

Even when it is not a traditional practice, bedsharing is valued by many New Zealand families. Parents report that it permits close contact and response to infant needs through the night, ease of breastfeeding, and a sense of security. For many it is a chosen, infant-centered parenting style. In some places, such as Japan and Hong Kong, bedsharing is common and SIDS is uncommon; it cannot be said, therefore, that bedsharing is uniformly risky. It must be noted that in cultures that bedshare but have low risks of SIDS, the surface slept upon is usually very firm. Also, very few mothers in these cultures smoke (although smoking among fathers is quite common). (22,23)

An in-depth examination of the New Zealand study found that bedsharing appeared to be a significant risk factor for sudden death only if the mother had smoked during her pregnancy. Smoking among fathers had no effect. Moreover, there was a strong interaction between bedsharing and smoking, with each factor by itself being relatively small (about double the risk). When both factors were present, however, the risk was five times higher than when neither factor was present. This effect was present in all racial groups.

The fact that 60 to 70 percent of Maori infants bedshare, and that a similar percentage of Maori mothers smoke during pregnancy, thus explains to some degree the persistence of high rates of SIDS in the Maori population. Add to this the other elements of social deprivation that are endured by Maori, and a "good enough" explanation of high SIDS rates is found. Furthermore, this explanation accounts for the low SIDS rates in Japan and Hong Kong, where mothers rarely smoke.

Clearly, there are safe and unsafe ways of bedsharing, and we are working to identify the exact mechanisms by which these combined bedsharing/smoking deaths occur. We've just completed a home-based study of the behavior, breathing, and temperature of 40 babies sharing a bed with their parents compared to 40 babies sleeping in a crib in the same room. We hope that this study will be another step forward in identifying safer ways for babies to share beds with their parents.

Some evidence now suggests that when exposed to the harmful effects of tobacco in the womb, babies sustain damage to their nervous systems that affects their ability to respond well to the interactions between mother and infant that often occur in bedsharing.

One of bedsharing's clear benefits is that it makes it much easier to breastfeed more frequently. There is considerable evidence that breastfeeding continues for longer in those families who regularly share the bed with their babies. There is little or no evidence to suggest that infant behavior problems and bonding are improved or made worse by bedsharing, although few studies of this issue were done well enough to trust the conclusions.

With the current state of evidence, we believe that if a mother has smoked in pregnancy, her baby should go into a shared bed only for breastfeeding and cuddles, and that, when the mother is about to go to sleep, the baby should be put down to sleep in a crib in the same room for at least the first six months of life. For mothers who have not smoked in pregnancy and who are not on sedative drugs, bedsharing presents either no or minimal risk to the baby. So far, we have not identified a group of infants for whom bedsharing lowers the risk of SIDS. (24)

* Recommendation put forth by Sally Abel et al., "Infant Care Practices: A Qualitative Study of the Practices of Auckland Maori, Tongan, Samoan, Cook Island, Niuean, and Pakeha Caregivers of Under 12 Month Old Infants," The Infant Care Practices Study Team, Department of Maori and Pacific Health (1999): 10.

NOTES

(1.) E. A. Nelson et al., "Postneonatal Mortality in South New Zealand: Necropsy Data Review," Paediatr. Perinat. Epidemiol. 3, no. 4 (1989): 375-385.

(2.) E. A. Mitchell et al., "Four Modifiable and Other Major Risk Factors for Cot Death: The New Zealand Study," J. Paediatr. ChfidHealth 28, no. 1 (1992): S3-8.

(3.) E. A. Mitchell et al., "The New Zealand Cot Death Study: Some Legal and Ethical Issues," J. Paediatr. Child Health 28, no. 1 (1992): S17-20.

(4.) E. A. Mitchell et al., "Postnatal Depression and SIDS: A Prospective Study," J. Paediatr. Child Health 28, no. 1 (1992): S13-16.

(5.) R. P. Ford et al., "Breastfeeding and the Risk of Sudden Infant Death Syndrome," Intl. J. of Epidemiology 22, no. 5 (1993): 885-890.

(6.) E. A. Mitchell et al., "Smoking and the Sudden Infant Death Syndrome," Pediatrics 91, no. 5 (1993): 893-896.

(7.) E. A. Mitchell et al., "Ethnic Differences in Mortality from Sudden Infant Death Syndrome in New Zealand," BMJ 306, no. 6869 (1993): 13-20.

(8.) R. Scragg et al., "Bed Sharing, Smoking, and Alcohol in the Sudden Infant Death Syndrome," BMJ 307, no. 6915 (1993): 1312-1318.

(9.) E. A. Mitchell et al., "Travel and Changes in Routine Do Not Increase the Risk of Sudden Infant Death Syndrome," Acta Paediatrica 83, no. 8 (1994): 815-818.

(10.) C. A. Wilson et al., "Clothing and Bedding and Its Relevance to Sudden Infant Death Syndrome: Further Results from the New Zealand Cot Death Study," J. Paediatr. Child Health 30, no. 6 (1994): 506-512.

(11.) A. J. Stewart et al., "Antenatal and Intrapartum Factors Associated with Sudden Infant Death Syndrome in the New Zealand Cot Death Study," J. Paediatr. Child Health 31, no. 5 (1995): 473-478.

(12.) R. P. Ford et al., "Allergy and the Risk of Sudden Infant Death Syndrome," Clinical & Exper. Allergy 26, no. 5(1996): 580-584.

(13.) R. K. Scragg et al., "Infant Room-Sharing and Prone Sleep Position in Sudden Infant Death Syndrome," The Lancet 347, no. 8993 (1996): 7-12.

(14.) B. J. Taylor et al., "Symptoms, Sweating and Reactivity of Infants Who Die of SIDS Compared with Community Controls," J. Paediatr. Child Health 32, no. 4(1996): 316-322.

(15.) S. M. Williams et al., "Sudden Infant Death Syndrome: Insulation from Bedding and Clothing and Its Effect Modifiers," Intl. J. of Epidemiology 25, no. 2 (1996): 366-375.

(16.) R. R Ford et al., "SIDS, Illness, and Acute Medical Care," Arch. Dis. Child. 77, no. 1 (1997): 54-55.

(17.) R. P. Ford et al., "Heavy Caffeine Intake in Pregnancy and Sudden Infant Death Syndrome," Arch. Dis. Child. 78, no. 1 (1998): 9-13.

(18.) E. A. Mitchell et al., "Changing Infants' Sleep Position Increases Risk of Sudden Infant Death Syndrome," Arch. Pediatr. Adolesc. Med. 153, no. 11 (1999): 1136-1141.

(19.) R. K. Scragg et al., "Maternal Cannabis Use in the Sudden Infant Death Syndrome," Acta Paediatr. 90, no. 1 (2001): 57-60.

(20.) E. A. Mitchell et al., "Dummies and the Sudden Infant Death Syndrome," Arch. Dis. Child. 68, no. 4 (1993): 501-504.

(21.) E. A. Mitchell et al., "Risk Factors for Sudden Infant Death Syndrome Following the Prevention Campaign in New Zealand: A Prospective Study," Pediatrics 100, no. 5 (1997): 835-840.

(22.) E. A. Nelson and B. J. Taylor, "International Child Care Practices Study: Infant Sleep Position and Parental Smoking," EarlyHum. Dev. 64, no. 1 (2001): 7-20.

(23.) E, A. Nelson et al., "International Child Care Practices Study: Infant Sleeping Environment," EarlyHum, Dev. 64, no. 1 (2001): 43-55.

(24.) R. K. R. Scragg and E. A. Mitchell, "Side Sleeping Position and Bedsharing in Sudden Infant Death Syndrome," Ann. Med. 30 (1998): 345-349.

Barry Taylor, MBChB, FRACP, is a professor of pediatrics and child health at the University of Otago and is also chairman of the New Zealand National Child and Youth Health Mortality Review Committee. Sally Baddock, BSc, Dip Tchg, is a junior research fellow at the University of Otago and a PhD candidate. Rodney Ford, MD, FRACP, is a community pediatrician in Christchurch. Ed Mitchell, MBBS, FRACP, DCH, DSc (Med), is a New Zealand Child Health Research Foundation professor at the University of Auckland. David Tipene-Leach, MBChB, DcomH, MCCMNZ, is a primary care physician and medical adviser for the Maori SIDS Prevention Team. Barbara Galland, PhD, is a senior research fellow in the Department of Women's and Children's Health, University of Otago.

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