E. A. Mitchell

Smoking and the Sudden Infant Death Syndrome

The aims of this review are (a) to critically examine the epidemiologic evidence for a possible association between smoking and the sudden infant death syndrome (SIDS), (b) to review the pathology and postulated physiological mechanism(s) by which smoking might be causally related to SIDS, and (c) to provide recommendations for SIDS prevention in relation to tobacco smoking. Over 60 studies have examined the relation between maternal smoking during pregnancy and risk of SIDS. With regard to prone-sleep-position intervention programs, the pooled relative risk associated with maternal smoking was RR = 2.86 (95% CI = 2.77, 2.95) before and RR = 3.93 (95% CI = 3.78, 4.08) after. Epidemiologically, to distinguish the effect of active maternal smoking during pregnancy from involuntary tobacco smoking by the infants of smoking mothers is difficult. Clear evidence for environmental tobacco smoke exposure can be obtained by examining the risk of SIDS from paternal smoking when the mother is a non-smoker. Seven such studies have been carried out. The pooled unadjusted RR was 1.49 (95% CI = 1.25, 1.77). Consideration of the pathological and physiological effects of tobacco suggests that the predominant effect from maternal smoking comes from the in utero exposure of the fetus to tobacco smoke. Assuming a causal association between smoking and SIDS, about one-third of SIDS deaths might have been prevented if all fetuses had not been exposed to maternal smoking in utero.

Factors associated with the duration of breastfeeding

A cohort study of healthy term infants was conducted to identify factors associated with breastfeeding duration. Three hundred and fifty mothers delivering in one obstetric hospital in Auckland, New Zealand were recruited. Ninety‐five percent were followed up until 1 y. Breastfeeding was initiated by 97.4%, the median duration of breastfeeding was 7.6 mo, and 30% were continuing some breastfeeding at 12 mo. Adjusted risk ratios for shorter duration of breastfeeding were: maternal age < 25 y, 2.33 (95% confidence interval = 1.33, 4.05); maternal age 25–34, 1.45 (1.01, 2.09) compared to maternal age ≥ 35; planning to cease breastfeeding ≤ 6 mo, 2.39 (1.65, 3.46); planning to breastfeed for as long as possible, 1.48 (1.00, 2.18), or not knowing plans 2.13 (1.36, 3.32) when compared to planning to cease breastfeeding after 6 mo; inverted nipples, 2.02 (1.26, 3.23), daily dummy use 1.62 (1.20, 2.18) or use of formula in the first month 2.79 (2.05, 3.80). Reporting mastitis, 0.67 (0.48, 0.94), and sharing the mothers bedroom at 3 mo, 0.69 (0.51, 0.92) were associated with a reduced risk for shorter duration of breastfeeding. We recommend that during the antenatal period attention be directed at mothers plans for duration of breastfeeding, that mothers be encouraged to have their baby in their bedroom, and that the use of formula and dummies should be discouraged in the first months of life.

Dummies and the sudden infant death syndrome.

The association between dummy use and sudden infant death syndrome (SIDS) was investigated in 485 deaths due to SIDS in the postneonatal age group and compared with 1800 control infants. Parental interviews were completed in 87% of subjects. The prevalence of dummy use in New Zealand is low and varies within New Zealand. Dummy use in the two week period before death was less in cases of SIDS than in the last two weeks for controls (odds ratio (OR) 0.76, 95% confidence interval (CI) 0.57 to 1.02). Use of a dummy in the last sleep for cases of SIDS or in the nominated sleep for controls was significantly less in cases than controls (OR 0.44, 95% CI 0.26 to 0.73). The OR changed very little after controlling for a wide range of potential confounders. It is concluded that dummy use may protect against SIDS, but this observation needs to be repeated before dummies can be recommended for this purpose. If dummy sucking is protective then it is one of several factors that may explain the higher mortality from SIDS in New Zealand than in other countries, and may also explain in part the regional variation within New Zealand.

Influences on breastfeeding in southeast England

Factors associated with not exclusively breastfeeding at discharge from the obstetric hospital and with duration of breastfeeding were examined in 700 randomly sampled infants. Obstetric records were examined in 97.7% of the subjects and 73.0% of subject families were interviewed. There were 444 (66.5%) infants exclusively breastfed at discharge from the obstetric hospital. Factors associated with not exclusively breastfeeding at discharge from the obstetric hospital after adjusting for potential confounders were: mother leaving school aged less than 18 years, mother not attending antenatal classes and the use of a dummy in the 2 weeks before the interview. Bed sharing practice in the 2 weeks before the interview was associated with exclusively breastfeeding at discharge from the obstetric hospital. Factors associated with a shorter duration of breastfeeding were: mother leaving school before 18 years of age, smoking 20 or more cigarettes per day and use of a dummy. Dummy use may causally reduce breastfeeding or might be a marker for breastfeeding difficulties. There was a doseresponse relationship with smoking, with heavier smokers breastfeeding for the shortest time periods. Bed sharing was associated with a longer duration of breastfeeding. This may not necessarily be a causal relationship because breastfeeding may promote bed sharing. The effect of dummy use and bed sharing on breastfeeding warrants further study.

International trends in postneonatal mortality.

Trends in mortality in the age groups 1-5 and 6-11 months from 1966 to 1987 for Australia, Canada, England and Wales, New Zealand, and Sweden were examined. Mortality rates for ages 1-5 months differed appreciably between countries, with Sweden lower than all other countries examined. Rates have decreased in Australia, Canada, and England and Wales, but increased in New Zealand and Sweden. Mortality reported as due to the sudden death syndrome (SIDS) increased dramatically in all countries, although much of the increase was probably due to diagnostic transfer from respiratory diseases. Over 80% of SIDS deaths occurred in the age group 1-5 months and SIDS accounted for about half of all deaths in this age group. For developed countries total mortality in those aged 1-5 months was an indirect measure of SIDS mortality. A real increase in SIDS has thus occurred in Sweden and New Zealand and possibly in other countries as well. Mortality in the age group 6-11 months has approximately halved in all countries examined over the study period.

Risk factors for SIDS.

We already know enough, the challenge is how to change behaviour

an adequate cause of death

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Factors Associated With the Duration of Breastfeeding

A cohort study of healthy term infants was conducted to identify factors associated with breastfeeding duration. Three hundred and fifty mothers delivering in one obstetric hospital in Auckland, New Zealand were recruited. Ninety-five percent were followed up until 1 y. Breastfeeding was initiated by 97.4%, the median duration of breastfeeding was 7.6 mo, and 30% were continuing some breastfeeding at 12 mo. Adjusted risk ratios for shorter duration of breastfeeding were: maternal age <25 y, 2.33 (95% confidence interval = 1.33, 4.05); maternal age 25-34, 1.45 (1.01, 2.09) compared to maternal age > or =35; planning to cease breastfeeding < or =6 mo, 2.39 (1.65, 3.46); planning to breastfeed for as long as possible, 1.48 (1.00, 2.18), or not knowing plans 2.13 (1.36, 3.32) when compared to planning to cease breastfeeding after 6 mo; inverted nipples, 2.02 (1.26, 3.23), daily dummy use 1.62 (1.20, 2.18) or use of formula in the first month 2.79 (2.05, 3.80). Reporting mastitis, 0.67 (0.48, 0.94), and sharing the mothers bedroom at 3 mo, 0.69 (0.51, 0.92) were associated with a reduced risk for shorter duration of breastfeeding. We recommend that during the antenatal period attention be directed at mothers plans for duration of breastfeeding, that mothers be encouraged to have their baby in their bedroom, and that the use of formula and dummies should be discouraged in the first months of life.