Smoking in pregnancy

Current

1 Obstetrics

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Smoking in pregnancy

P. Gillies and M. Wakefield Given that 1 in 3 women smoke during pregnancy, smoking is a significant source of morbidity and mortality in fetuses, infants and women themselves. It has been estimated that 4300 miscarriages each year in the UK are smoking-related and low birth weight, placenta praevia, placenta abruptia and sudden infant death syndrome add considerably to this toll. In addition, babies born to mothers who smoke during pregnancy suffer from poor intellectual and physical growth and are more likely to have respiratory ailments, asthma and glue ear. In women in Britain, lung cancer has overtaken breast cancer as a cause of death, reflecting the increasing prevalence of smoking in women over the last 4 decades. Women feel that smoking confers certain positive benefits, such as the ability to control mood and it is a relatively inexpensive form of enjoyment. Those who smoke during pregnancy tend to be younger, unmarried, of poor educational attainment, lower occupational status, socially disadvantaged, feel addicted to smoking and, importantly, have a partner who smokes. Interventions to help women to stop smoking during pregnancy and beyond have been successful in ante-natal clinic settings, particularly when personal&d. Such interventions, by encouraging smoking cessation or reinforcing cessation in women who give up early in pregnancy, also appear to influence birth weight and are therefore of major public health significance.

1 in 3 adult men and women in the UK smoke cigarettes.’ The disastrous health consequences for over 100000 individuals each year from the resulting smoking-related diseases of cancer of the lung, bladder, renal pelvis and pancreas, respiratory ailments and cardiovascular conditions,* continue to make heavy demands upon health service resources. In addition, the effects of smoking in pregnancy on the fetus and of passive smoking in the home

environment on infant health and well-being, are varied and well-documented.3 Whilst a national survey of smoking in pregnant women in the UK has yet to be reported, regional studies suggest that 1 in 3 pregnant women smoke.4 Furthermore, as in the general population in which there is a clear socio-economic gradient, smoking is more prevalent in those pregnant women of poorer socio-economic status,4 particularly those suffering material deprivation and financial hardship.5 The prevalence and magnitude of the problem of cigarette smoking is therefore one of considerable clinical and public health concern, especially in areas of socio-economic disadvantage. This paper briefly

P. Gillies, Department of Public Health Medicine and Epidemiology, University of Nottingham, Clifton Boulevard, Nottingham NG7 2UH, UK, M. Wakelield, Behavioural Epidemiology Unit, South Australian Health Commission, Adelaide. Australia Current Obsrerrics and Gynaecolog.v(1993) 3. IS?-161 80 1993 LongmanGroup UK Ltd

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reviews: recent evidence on the health effects of smoking in pregnancy for the fetus and child; the reasons women give for continuing to smoke during pregnancy and the efforts made thus far to encourage smoking cessation in the ante-natal period.

Health effects Maternal smoking during pregnancy

Good evidence exists to indicate that smoking during pregnancy causes the following: l low birth weight l spontaneous abortion 0 perinatal mortality l sudden infant death syndrome (SIDS) l poor intellectual development in childhood l impairment of physical growth Low birth weight in the babies of women who smoke during pregnancy results from intrauterine growth retardation due to nicotine and carbon monoxide acting to reduce fetal oxygenation causing fetal hypoxia. The independent and additive mechanisms operating are high levels of carboxyhaemoglobin in the smoking mother which leads to a decrease in oxygen unloading to the fetus combined with an acute nicotine-induced vasoconstriction of maternal blood supply to the placenta. The intrauterine growth retardation leading to a lower birth weight appears to be symmetrical, with a reduction in crown to heel birth length. There is incontravertible evidence from epidemiological studies to show that women who smoke are three times more likely than those who do not, to have a baby weighing 200 g lighter on average.‘j This effect is greater in older women over 35 years and is dose-related, not simply to the number of cigarettes women report they consume but to the carbon monoxide yield of the cigarettes smoked, although there may be a threshold effect.’ One recent study has demonstrated that women who both smoke and drink heavily compared with those who do neither, have babies which are on average 500 g lighter.* Alcohol and tobacco probably therefore have additive harmful effects. The impact of smoking on birth weight has, however, been found to be independent of alcohol consumption, maternal age, socio-economic status, weight and height, weight gain during pregnancy, parity, race and the sex of offspring.g The likelihood that maternal smoking exerts a direct effect on birth weight is further strengthened by the results of clinical trials that demonstrate a significant improvement in birthweight among women who stop smoking during pregnancy. l”*ll Several studies have demonstrated that maternal exposure to environmental tobacco smoke is independently associated with a reduction in mean birthweight. 12*13Further studies are however required in order to provide a reliable estimate of the contribution of such exposure.

Spontaneous

abortion. The Royal College of Physicians recent report on smoking and the young estimated that there were 4300 smoking-related miscarriages each year in England and Wales. The spontaneous abortion rate in smoking women is 27% higher than that in non-smoking women. The report notes that for young mothers under 30 years, smoking increases the likelihood that they will abort a potentially normal fetus. For older mothers, smoking increases the chance of chromosomal abnormalities which result in spontaneous abortion. Perinatal mortality. Smoking

significantly increases the likelihood of loss of the fetus from 28 weeks gestation up to the first 7 days of life. Maternal smoking is associated with a significant increase in the risk of placental abruption,i4 placenta praevia,” bleeding early or late in pregnancy and pre-term premature rupture of membranes,16 all of which carry high risks of pre-term birth and perinatal loss. It has been calculated that 30% of the excess deaths of smokers’ babies could be attributed to the increased likelihood of placenta praevia, abruption and ante partum bleeding.” Pre-term delivery is twice as common in smokers, particularly in older women, la and the number of perinatal deaths attributable to smoking each year in England and Wales has been estimated to be 420.’ Sudden Infant Death Syndrome. SIDS occurs with a peak incidence of 2-4 months of age. Ante-natal factorslg as well as risk factors during a period of postnatal vulnerability may predispose an infant to SIDS.20 Maternal smoking during pregnancy is an independent risk factor for SIDS. Women who smoke are 1.5-5 times more likely to lose their infant to SIDS than women who do not smoke. A doseresponse relationship exists between this risk and levels of -cigarette consumption.2’ Maternal smoking has also been associated with the time of death, in that early SIDS deaths between 7 and 67 days are more strongly related to maternal smoking.ig It has been estimated that approximately 27% of SIDS deaths are attributable to maternal smoking.lg A residual effect of maternal smoking after adjustment for birth weight may reflect passive smoking by the infant in the home from maternal and/or paternal smoking. Dwyer and Posonby have noted that more research is needed to establish whether this latter outcome is mediated principally through respiratory illness.20 Poor

intellectual development. There is a strong independent relationship between maternal smoking in pregnancy and lower educational attainment among young children. 22 Children of mothers who smoke in pregnancy perform at a significantly lower level on psychological tests of cognitive functioning relative to the children of ex-smokers, after adjustment for other potentially confounding factors. These findings are of concern when it is considered that

SMOKING IN PREGNANCY

modest cognitive differences in younger children have been found to translate into larger differences over time. Poor growth. Smoking during pregnancy has a longterm detrimental effect upon the physical growth and development of surviving offspring,23 resulting in decreases in both height and weight. Weaker evidence exists for a relationship between smoking during pregnancy and: l childhood cancersz4 l birth defects and l incidence of respiratory illnesses in children over and above any influence from passive postnatal smoking.’ In addition, women who smoke may find it more difficult to conceive in the first instance. Smoking probably reduces the chances of becoming pregnant in any given menstrual cycle, although as Baird points out in a concise review of the area,3 this should not be considered a method of birth control! The causal nature of the relationship between smoking and sub-fecundity must still be regarded somewhat tentatively due to the correlation between smoking and caffeine consumption, since it is still possible that coffee drinking rather than smoking may be the cause of the problem.

Passive smoking Infants of parents who smoke have significantly more respiratory illnesses such as bronchitis and pneumonia during the first year of life. They also demonstrate more signs of respiratory irritation, coughing, sputum production and wheezing and childhood asthma is strongly associated with parental smoking, particularly smoking by the mother. Symptoms of asthma are twice as common in the children of smokers. Middle ear disease or ‘glue ear’ is one of the most frequent causes of deafness in children and at least one-third of all cases are attributable to parental smoking. Passive smoking and ill health effects in children is reviewed in the latest Royal College of Physicians report.’ Smoking appears to interfere with the production of prolactin required for the production of breast milk and women who smoke may find it more difficult to breast-feed. They should, however, be encouraged to persist in their efforts since research shows that breast feeding decreases the risk of respiratory illness incurred by passive smoke exposure to parental cigarette smoke.25 Reasons for smoking in pregnancy Women who smoke during pregnancy are more likely than non-smokers to:4*26 l be younger

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be unmarried be Caucasian l have poor educational attainment l be of lower occupational status l be socially disadvantaged l be heavier smokers prior to pregnancy l live with a partner who smokes Women do not appear to smoke during pregnancy because they are ignorant of the adverse health effects. On the contrary, they tend to know about the basic hazards of the habit and report receiving most of their information from family, friends, the television and booklets distributed at ante-natal clinics. Only 1 in 4 women who smoke in pregnancy say that they remember receiving advice about smoking from general practitioners, midwives and obstetricians. This is not to say, necessarily, that health professionals are not providing such advice, but it does suggest that if they are, they are doing so in a way that is singularly unremarkable. Professional advice and information about smoking must also compete with the powerful influence of family and friends, many of whom have had normal pregnancy outcomes despite being smokers. Addiction to nicotine is the most common reason given by women themselves for smoking during pregnancy2’ and nicotine has been formally recognised by the US Surgeon General as an addictive substance. Other reported reasons for smoking include mood control, that is, to relax or calm nerves, enhanced enjoyment and to relieve boredom. Smoking is therefore perceived by women to have many positive benefits. Social influences to continue to smoke are also very important. Simply being in the company of smokers means that cigarettes are usually available, so that the opportunity, as well as the temptation to smoke, is frequently present. Women who have many friends who smoke, especially those with partners who smoke, find it more difficult to stop smoking. Among working class groups of women, such social influences to smoke are particularly strong.28 l

l

Smoking cessation during pregnancy Most studies show that between 25 and 30% of women smokers stop smoking spontaneously during their pregnancy, particularly in the first trimester when there is more benefit to the fetus. More than half of those who do manage to quit for the duration of pregnancy are, however, likely to take up the habit again once their baby is born,26 and after delivery only 8-10% are likely to remain long-term ex-smokers. This is none-the-less higher than the long-term quit rate among women who are not pregnant. Pregnancy therefore offers a unique opportunity to tackle the smoking issue. The challenge for health professionals and health educators is to intervene to encourage women to stop smoking not only during pregnancy but for a much longer period.

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The Royal College of Physicians has stated that provision and planning of smoking cessation services during ante-natal care is currently inadequate in the UK and should be improved, with GPs, obstetricians and midwives all having a critical role to play.g Impact of smoking cessation intervention in pregnancy

There is now sound evidence from trials conducted around the world (see Table), that interventions to help women give up smoking during pregnancy can be effective in increasing cessation and reducing tobacco consumption up to the babies birth and for at least 6 months thereafter. Interventions which attempt to personalise the advice offered, which offer friendly support, encouragement and counselling and which focus on the anticipated benefits to women themselves from giving up smoking as well as on benefits to the baby, appear to be most successful. The provision of simple coping and behaviour change strategies are also important for effective intervention. Programmes which recruit women at the earliest possible stage in pregnancy have the greatest likelihood of success. Whilst it is true to say that intensive behavioural approaches in extremely well-funded demonstration projects have proven to have the largest impact on smoking cessation, as the Table shows, well-conceived simpler strategies also have a significant impact. Appropriate obstetrician, GP or midwife advice and counselling, self-help booklets and materials shown or distributed in the ante-natal period, with relevant messages reinforced throughout pregnancy can promote smoking cessation. Interventions which incorporate post partum reinforcement for cessation and Table 1 -Anti-smoking Author

which encourage partners’ cessation, may hold the promise of further increasing long-term quit rates, although these intervention components are yet to be formally evaluated. The effect of intervention during pregnancy is not solely confined to womens’ smoking but also extends to the health of the fetus. Two studies have found a significant effect of intervention on birthweight outcome.‘O~” The sample sizes in many other studies evaluating interventions have unfortunately not been large enough to detect a statistically significant impact on birthweight. None-the-less the quality of the evidence available thus far provides a powerful argument for expending resources on smoking cessation efforts in pregnancy, particularly in the light of the fact that perinatal care attributable to smoking probably costs the NHS in the UK millions of pounds each year. g Resource limitations and the need for efficient management practices do mean that interventions must not only be cost-effective but practicably feasible within the existing planning constraints of ante-natal care. Data suggests that interventions of the type described are indeed costeffective34 and feasible. Smoking cessation advice to pregnant women should be: universal and demanded by purchasing authorities from provider units under the new Health Service contracts. (RCP, 1992, p 9). Translating such policy into systematic practice to consider may require health professionals additional training to acquire the appropriate effective health education skills. They can however embark upon the process in the knowledge that their efforts

interventions in pregnancy and their effect on womens’ smoking and their babies’ weight Year and country

Type of intervention

Type of study

Donovan”

1977 UK

Advice by doctor

Sexton & Hebell’

1984 USA

Home visit; advice; phone call; mail

Windsor et a13’

1985 USA

MacArthur et al”

1987 UK

Ershoff et al3i

1989 USA

Hjalmarson et al”’

1991 Sweden

Gillies

1992 UK

Outcome Womens’ smoking

Birthweight

Random&d controlled trial (RCT) RCT

Decreased consumption

No effect

Decreased consumption. Increased cessation

Counselling; booklet; selfhelp guide

RCT

Advice by obstetrician; leaflet 8 booklets mailed to home in ante-natal period Self-help manual of strategies from obstetrician Counselling; carbon monoxide feedback; booklet

RCT

Decreased consumption. Increased cessation Decreased consumption

Significantly heavier babies in experimental group (Pi 0.05) Not recorded

Heavier first born babies (PcO.06) Not recorded

RCT

Increased cessation

Controlled Trial (CT)

Increased cessation

Not recorded

CT

Maintaining non-smoking + cessation 6 months post partum

33 g difference (not significant)

SMOKING IN PREGNANCY

are likely to be positively beneficial to the health and welfare of the women and babies in their care in both the short and longer-term. Acknowledgements This article was prepared whilst Dr Gillies was a Harkness Fellow of the Commonwealth Fund of New York at the Harvard School of Public Health.

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References 21. I. Office of Population Censuses and Surveys General

Household Survey 1988, 1990, London: HMSO 2. International Agency for Research on Cancer Monograph on the evaluation of the carcinogenic risk of chemicals to humans. Tobacco smoking. Lyon: IARC. 1986 3. Poswillo D. Alberman E. Effects of smoking on the fetus, neonate and child. Oxford: Oxford University Press, 1992 4. Madeley RJ, Gillies PA, Power FL Symonds EM. Nottingham Mothers Stop Smoking Project - baseline survey of smoking in pregnancy. Comm Med 1989; 11: 124-130 5. Graham H. Smoking among working class mothers with children: a final report. Report to the Department of Health, London, 1992 6. Tenovuo AH, Kero PA, Korvenranta HJ, et al. Risk factors associated with severely small for gestational age neonates. Am J Perinatology 1988; 5: 267-71 I. Peacock JL, Bland JH, Anderson HR, Brooke OG. Cigarette smoking and birthweight: type of cigarette smoked and possible threshold effect. Internat J Epidemiol 1991; 20: 405-412 8. Olsen J, Pereira A-da-C, Olsen SF. Does maternal tobacco smoking modify the effect of alcohol on fetal growth? Am J Public Health 1991; 81: 69-73 9. Royal College of Physicians. Smoking and the Young, Lavenham: Lavenham Press, 1992 10. Sexton M, Hebel JR. A clinical, trial of change in maternal smoking and its effects on birthweight. JAMA, 1984; 251: 911-915 II. MacArthur C, Newton JR, Knox EG. Effect of anti-smoking health educaiton on infant size at birth: a randomized controlled trial. Brit J Obstet Gynaecol 1987; 94: 295-300 12. Rubin DH, Krasihnikoff PA, Leventhal JN, Weile B, Berget A. Effect of passive smoking on birthweight. Lancet 1986; 2: 415-417 13. Haddow JE, Knight GJ, Palomaki GE, McCarthy JE. Second trimester serum cotinine levels in non-smokers in relation to birthweight. Am J Obstet Gynaecol 1988; 159: 481-484 14. Voigt LK, Hollenbach KA, Krohn MA, Daling JR, Hickok DE. The relationship of abruptio placentae with maternal smoking and small for gestational age infants. Obstet Gynecol 1990; 75: 771-774 15. Kramer MD, Taylor V, Hickok DE, Daling JR, Vaughan TL, Hollenbach KA. Maternal smoking and placenta praevia. Epidemiology 1991; 2: 221-223 16. Harger JH, Hsing AW, Tuomala RE. et al. Risk factors for

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