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Abstract

• Smoking doubles the risk of having a low-birthweight baby and significantly increases the rate of perinatal mortality and several other adverse pregnancy outcomes.
  
• The mean reduction in birthweight for babies of smoking mothers is 200 g.
  
• High quality interventions to help pregnant women quit smoking produce an absolute difference of 8.1% in validated late-pregnancy quit rates.
  
• If abstinence is not achievable, it is likely that a 50% reduction in smoking would be the minimum necessary to benefit the health of mother and baby.
  
• Healthcare providers perform poorly in antenatal interventions to stop women smoking. Midwives deliver interventions at a higher rate than doctors.
  
• The efficacy of nicotine replacement therapy has not been established in pregnancy. Currently, its use should only be considered in women smoking more than 10 cigarettes per day who have made a recent, unsuccessful attempt to quit and who are motivated to quit.
  
• Relapse prevention programs have shown little success in the postpartum period.

The relationship between smoking and birthweight has been heavily investigated, with studies involving over 500 000 births published by 1986.¹ By 1990, the evidence was strong enough for the US Surgeon General to conclude that maternal smoking definitely retarded fetal growth, causing an average reduction in birthweight of 200 g and doubling the risk of having a low-birthweight baby.² Women who quit smoking in the first 3-4 months of pregnancy have infants of equivalent birthweight to those who have never smoked.²

The relationships between smoking and other adverse pregnancy outcomes have also been widely studied. An Australian group synthesised studies on 10 pregnancy-related diseases and found that smokers had significantly increased risk of eight negative outcomes, including almost treble the rate of sudden infant death syndrome among their offspring (Box 1).³ A more recent study found that smoking was strongly associated with an elevated risk of placenta praevia, abruptio placentae, ectopic pregnancy and preterm premature rupture of the membranes (Box 1).⁴

Randomised trials of the effects of quitting indicate that abstinence is associated with a reduction in low birthweight (pooled OR, 0.80; 95% CI, 0.67-0.95) and in the incidence of preterm birth (pooled OR, 0.83; 95% CI, 0.69-0.99).⁵ Given the very low power of relevant trials, it is not surprising that differences in other, less common negative pregnancy outcomes were not detected.

If maternal smoking in pregnancy has a lasting impact on the child's long-term physical and mental development, the effect is likely to be small and of uncertain clinical significance.⁶ One recent review found that effects on children's physical development were related to maternal cigarette consumption during pregnancy, suggesting a dose-response relationship.⁷ For intellectual development, Fried emphasised that smoking and other drug use accounted for less than 5% of the variance associated with cognitive outcome, whereas other lifestyle factors accounted for up to 35% of this variability.⁸

Prevalence of smoking in pregnancy

International data do not indicate a clear trend towards reduced smoking in pregnancy in developed countries.⁹ Sweden, a country which has conducted a sustained campaign to reduce smoking by pregnant women, provides a rare example where a decline has been systematically documented.¹⁰ In 1983, 29% of pregnant Swedish women smoked daily, and by 1997 this had reduced to 15%.¹⁰

In Australia, there have been no long-term serial data on trends in smoking in pregnancy.⁹ Recent data from New South Wales indicate a small decrease from 22.1% in 1994 to 19.8% in 1998.¹¹ However, smoking prevalence may be much higher in women attending public hospital antenatal clinics, with three Australian studies published in the 1990s reporting proportions of 35%-38%.⁹

While up to one in three smokers quit when pregnancy is planned or after confirmation of pregnancy,⁹ research indicates that many pregnant women who smoke are not especially motivated to quit. Intervention programs should focus on increasing readiness to quit.¹²

Healthcare provider performance

Healthcare providers are well placed to inform and influence pregnant smokers to quit, but many do not routinely deliver quit smoking interventions.¹³ In Australia, most pregnant smokers are identified, but only a minority are counselled about how to quit.¹⁴ Nurses report offering more counselling on quitting smoking than general practitioners and obstetricians.¹⁴ In a UK study of midwives, general practitioners and obstetricians, most reported experiencing difficulty and lack of enjoyment when giving counselling on quitting smoking.¹⁵ Just 28% of these practitioners thought they possessed the necessary skills and 53% perceived themselves to be insufficiently trained. Australian research also suggests that lack of training is a barrier, together with insufficient staff and lack of institutional smoking intervention policies.¹⁴ In the mid-1990s, very few Australian antenatal clinics had relevant written policies (4%) or offered in-service training in quit-smoking interventions (12%).¹⁴

Despite the difficulties, there is encouraging evidence that antenatal staff are more likely to provide smoking cessation counselling than healthcare providers in other settings.¹⁶ Training and institutional support can build on this platform.¹⁷

Efficacy of interventions

A Cochrane review of 34 trials reported a significant reduction in smoking in the intervention groups (odds ratio, 0.53; 95% CI, 0.47-0.60),⁵ an absolute difference of 6.4% in the number of women continuing to smoke. In the eight trials with high-intensity interventions, high-quality study methodology and validated measurement of smoking cessation, the resulting absolute difference in quit rates was 8.1%.

The prevention of relapse after pregnancy remains problematic. More than two out of three women who quit during pregnancy resume smoking by six months postpartum.¹⁸ Five trials of smoking relapse prevention pooled in the Cochrane review showed no significant difference in favour of treatment.⁵

Recently, biochemical measurements have been recommended as indicators of harm reduction in pregnant smokers.¹⁹ One study found a 92 g increase in mean birthweight for babies of women with a reduction of 50% or more in saliva cotinine levels.¹⁹ However, the value of such approaches is likely to be vigorously debated. Hebel et al found that the benefits of decreased smoking for birthweight were almost entirely restricted to those who quit completely.²⁰ On the other hand, a recent large Australian trial of a quit-smoking intervention that found no significant effect on quit rates did find that babies born to women in the intervention group were on average significantly heavier (84 g) than the babies of smoking women in the control group, which suggests that reduced smoking may have a positive effect.²¹

Regardless of the debate about goals, the evidence in favour of routinely counselling pregnant women to quit smoking is sufficiently strong for the US Preventive Services Task Force to give it the highest category recommendation (Category A).²² This is higher than the recommendation given to other common clinical activities, such as routine screening for iron-deficiency anaemia in pregnancy (Category B) or for gestational diabetes mellitus (Category C).²²

Quit-smoking interventions for pregnant women

Although effectiveness has been most clearly documented for cognitive behavioural programs,¹³ it is difficult to make recommendations about what specific components should be included in an intervention because of the diversity of methods tested.⁵ Group programs are very poorly attended and are not recommended.¹³ Self-help materials appear to be useful, especially when used in the populations for whom they were developed.^13,16 Box 2 summarises what is known about the effectiveness of different components.

Without being inappropriately prescriptive, four main components of smoking cessation interventions are recommended in pregnant and non-pregnant populations alike: assessment, advice, assistance with quitting and follow-up.

Assessment

Mullen et al have shown that simple changes in question format (away from requiring yes/no answers towards allowing responses such as "I used to smoke" or "I have cut down") increase smoking disclosure.²³ Women who report quitting recently have higher rates of inconsistent biochemical measures of smoking, so more detailed questioning of these women is appropriate.

Advice

Advice should provide specific risk information tailored to the woman's current state of knowledge. For example, women who reject the scientific evidence, countering it with anecdotal information, will require fuller discussion to overcome their misconceptions. Analogies about the effects of nicotine, carbon monoxide and tar may help to clarify the risks.

It is in the healthcare provider's interest to record in the notes that advice to quit smoking has been given.

Assistance

This is probably the most important component, but also the one most commonly omitted by antenatal care providers.¹⁴ A useful starting point is to check whether the woman has already attempted to quit and is contemplating attempting to quit now. If the woman is not contemplating quitting, an attempt should be made to identify why and to respond and motivate appropriately. There may be a need to counter specific self-exemptions, such as "It's good to have a smaller baby" or "I only smoke low tar cigarettes", or to address specific concerns, such as the need for smoking as relaxation. In women who are ready to stop, it is valuable to negotiate a target quit date. People who set a definite quit date are most likely to make a serious attempt.²⁴

Subsequent counselling should aim to develop some behavioural aids to quitting (Box 3). Specific concerns about quitting, such as fear of weight gain or withdrawal symptoms, may need to be addressed. Self-help materials can help in this counselling by saving time and reinforcing advice. Many women are situational smokers and will need help to cope with those situations. The woman's partner plays a crucial role in influencing the success of quitting.²⁵ A US study of 688 pregnant smokers found that women whose partners were non-smokers were significantly more likely to have quit smoking prenatally or in early pregnancy than women with smoking partners (58% and 35%, respectively).²⁵

Box 4 summarises an approach to promoting smoking cessation in pregnancy.

Follow-up

Because of the high frequency of relapse, follow-up, especially at the first postpartum visit, would appear to be a crucial component of a quit-smoking intervention. Unfortunately, in the absence of clear evidence of effectiveness, it is difficult to argue that doctors should invest substantial time in follow-up. Complementary efforts by those providing postnatal services may be required.

Nicotine replacement therapy

The efficacy of nicotine replacement therapy, combined with at least minimal behavioural assistance, has been well established in many non-pregnant populations.²⁶ Now that nicotine replacement therapy, both gum and patches, is available over-the-counter in Australia, some pregnant women would almost certainly be using it on their own initiative. However, such use remains controversial, as animal models have demonstrated that injected nicotine can cause fetal hypoxia and neonatal death, and has teratogenic effects.²⁷ Animal studies also suggest that there are higher rates of fetal resorption with continuous than with episodic nicotine exposure.²⁷ Clearly, therefore, there is a need to balance the pros and cons of nicotine replacement therapy in pregnancy.

Four small "physiological" studies cited by Oncken et al²⁷ did not identify any short-term deleterious effects on the fetus associated with nicotine replacement therapy, except for one unexpected finding where there was a high proportion of loss of fetal heart rate reactivity in the patch condition versus smoking (5/8 versus 1/6).

The only published trial of nicotine replacement therapy in pregnancy reported a high overall quit rate (26%) but no differences between intervention and placebo control groups.²⁸ However, the mean birthweight difference was 186 g higher (95% CI, 35-336) in the nicotine replacement therapy group.

Nicotine replacement therapy should only be considered in women smoking more than 10 cigarettes per day who have made a recent, unsuccessful attempt to quit and who are motivated to quit.

Bupropion

The use of antidepressants, including bupropion, for smoking treatment is not recommended in pregnancy. To date, there have been no published studies on their efficacy or risk-benefit ratio in pregnant women. Although the manufacturer is maintaining a database of cases where the most heavily promoted form of bupropion has been used in this population, the numbers are too small (n = 56) to draw any inferences at this stage. Bupropion is classified as a Category B2 drug with respect to use in pregnancy (ie, safety not established).

Conclusion

The efficacy of cognitive behavioural therapy for quitting smoking in pregnancy has been established. However, healthcare providers perform poorly in this area, particularly in providing counselling about how to stop. Training and institutional support is needed to improve their performance. The effort is well worthwhile: smoking is the most important modifiable cause of adverse pregnancy outcomes in developed nations.²

Acknowledgement

The preparation of this manuscript was funded by the New South Wales Cancer Council, Cancer Education Research Program.

References

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Authors' details

Centre for Health Promotion and Cancer Prevention Research, University of Queensland.
John B Lowe, DrPH, Director.

King Street Medical Practice, Newcastle, NSW.
Peter J Hopkins, MB BS(Hons), MMedSc, General Practitioner.

Reprints will not be available from the authors.
Correspondence: Dr Raoul A Walsh, Cancer Education Research Program, NSW Cancer Council, Locked Bag No 10, Wallsend, NSW, 2287.

©MJA 2001
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