Who stops smoking during pregnancy?
Abstract
Background. The proportion of women who stop smoking during pregnancy has varied between 17 and 40% percent in Sweden with a tendency of lower prevalence in recent years. The aim of the present study was to examine the factors that might influence the ability to stop smoking during pregnancy.
Method. One hundred and two women were interviewed shortly after their first visit to the antenatal clinic and a second time approximately one month after delivery. Two women who had late spontaneous abortions were excluded. The women were asked about background factors, smoking habits of their parents, smoking history and current smoking habits. The carbon monoxide in expiratory air was measured to verify reported smoking habits.
Results. Fifty-six of the 100 participating women had stopped smoking before the second interview. Having started smoking at an older age, having no previous children, smoking few cigarettes, a higher level of education, positive support from the partner and having lived with non-smoking parents were all associated with stopping smoking when tested as single factors. Reported smoking habits could be verified. Age, smoking habits of the partner, passive smoking at work, quality of sleep, general perceived health, length of sick-leave or amount of nausea were not correlated to stopping smoking.
Conclusion. The presence of several factors found to influence stopping smoking during pregnancy, and the tendency for smoking habits to be passed over to the new generation, are reasons for comprehensive and individualized, anti-smoking support.
Abbreviations:
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- ANC
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- ante-natal clinic
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- CO
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- carbon monoxide
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- VAS
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- visual analog scale
In earlier Swedish studies about 30% of pregnant women were reported to be regular smokers and about 70% of the smoking women continued to smoke throughout pregnancy in spite of encouragement by the ante-natal clinics (ANC) and other influences to stop smoking (1, 2). In 1995, however, only 17.2% of the women reported that they were smokers at the first visit to the ANC (3). In a study including women from three ANCs, the proportion of women stopping smoking during pregnancy varied between 20% and 40%, during a one-year period (1). These differences are interesting, since they might be caused by factors that could be influenced. Cnattingius et al. (4) showed that stopping smoking during pregnancy was associated with a higher level of education and a higher age at the start of smoking, while high parity, not living with the infant’s father, heavy smoking and daily passive smoking at home were associated with higher risk of continuing smoking.
The aim of the present study was to further examine the different factors that might influence the ability to stop smoking during pregnancy.
Material and methods
During a 10-month period, in 1994–5, all women who were smokers at the time of conception were asked by the midwife to participate in an interview concerning smoking and pregnancy, when they first attended any of nine participating ANCs in the south-western suburbs of Stockholm. They were contacted by telephone to arrange an appointment at their homes or at the local ANC. They were told about the nature of the study and that an objective test for smoking would be performed.
One hundred and two women were interviewed at the start of their pregnancy. The mean gestational week was 12; range 1–29. All of them were successfully contacted again after the delivery. One refused a second visit but answered the questions on the telephone. Two women had had spontaneous abortions and were excluded. Thirty-six women did not want to be interviewed. Their ages, social situations, parities and smoking habits at enlistment and at gestational week 32, when they are usually recorded in accordance with ANC routines, were checked in the ANC records. They were in general 1.8 years younger and lived slightly more often without a partner (n.s.) but had the same number of children as those interviewed.
A woman was defined as having stopped smoking if she reported that she had not smoked for at least one week at the second interview. During a 45 to 90 minutes discussion, the woman was briefly informed in a standardized way about the questionnaire and shown how to use the visual analog scale (VAS). She then filled in the form by herself. Efforts were made to prevent the partner and children from taking part.
The questionnaire had questions concerning age, social situation, level of education, age at start of smoking and the number and brand of cigarettes smoked at the time of conception. If the woman had stopped smoking, the gestational week for this was noted. A nicotine-consumption index was calculated by multiplying the number of cigarettes smoked each day by the nicotine content of each cigarette of the brand smoked. There were also questions concerning the smoking habits of her partner, his attitude to her smoking, the smoking history of the parents during her childhood, the occurrence of passive smoking at work, the presence of relatives or friends who had (had) a disease due to smoking, and sleep and general health from the Swedish Health-related Quality of Life Survey (5).
Sleep and health indices were calculated. The higher the index, the better the sleep or health. Questions concerning attitudes are shown in Table I. Ethnic origin was not recorded.
After filling in the questionnaire the woman’s carbon monoxide (CO) level in expiratory air was determined with a CO monitor (EC50, Bedfont Instruments, Upchurch, UK) (6). A cut-off value of 6–9 parts per million is frequently used to distinguish a smoker from a non-smoker (7). No one smoked during the interview.
A short informal chat about the answers always took place afterwards and, if the woman wished it, there was a general discussion about stopping smoking for 15–20 minutes.
A second meeting was arranged approximately four weeks after the expected day of delivery, always in the woman’s home. This interview started with questions and finished with a recording of the CO in expired air. The questions concerned current smoking status, smoking habits at week 32 of pregnancy, the gestational week when the woman stopped smoking, the amount of nausea during the first part of her pregnancy (VAS scale) and the duration of sick-leave during pregnancy.
Student’s t-test (means), the chi-square test (number of women) and the Mann-Whitney U-test (VAS scale) were used for evaluation of statistical differences. The level of significance was p<0.05.
Differences in mean ages were evaluated with 95% confidence intervals (C.I.). The correlation between the reported number of cigarettes and the CO in expired air was examined by Spearman’s correlation coefficient. Logistic regression was used to evaluate the relative importance of tested factors. The results are given as odds ratios (OR) with 95% C.I.
The study was approved by the Ethics Committee of the Karolinska Institutet, Stockholm, Sweden.
Results
A close correlation was found between the reported number of cigarettes smoked and the CO recorded (Spearman’s correlation coefficient=0.76) at the second interview. Only one woman wrongly reported her true smoking status, as judged from the CO results. She denied smoking, but her CO level was 12 parts per million.
Fifty-six of the 100 participating women managed to stop smoking before the second interview. Of these, twenty-five stopped before the 10th gestational week, sixteen between weeks 10 and 20, five between weeks 20 and 30, one between week 30 and the delivery, and nine immediately after delivery. An additional 15 women had refrained from smoking for a minimum of one week between the interviews but started smoking again.
The mean age of those who stopped smoking was 26.6 years and of those who continued 28.1 (95% C.I. for mean difference −3.63 to 0.57).
Women with no previous children stopped smoking more often than those with children (p<0.05).
Of those who had had nine years at school, 36% managed to stop, compared with 60% of those with 12 years and 75% of those with more than 12 years (p<0.05; nine years compared with higher education).
Those who stopped smoking smoked less than those who did not and thus had lower CO levels. The use of mild cigarettes (nicotine index) showed a poorer correlation to stopping smoking than a lower number of cigarettes.
Of those living with a non-smoking partner, 62% stopped smoking, while 52% of those with a smoking partner stopped (n.s.). Those who stopped more often stated that their partner encouraged them to stop smoking (p<0.05).
Exposure to passive smoking at work, health and sleep indices or amount of nausea experienced during pregnancy were not correlated to stopping smoking. Women with a relative or close friend who had had a tobacco-related disease (n=40) did not stop more often than those who had not.
The mean number of days on sick-leave for those who stopped smoking was 33 and 52 for those who did not (n.s.).
Fifteen women stated that, during their childhood, neither of their parents had smoked, while 85 had been brought up in families in which one or both parents smoked. Only four women with smoking parents smoked less than ten cigarettes per day. If neither of the parents was a regular smoker, 73% of the women stopped, on average in week 11. If only the mother had been a smoker, 71% stopped and, if only the father, 62%. If one of the parents had been a smoker the average stopping time was week 16. If both parents had been regular smokers, 44% managed to stop with the average stopping time in week 19 (p<0.05 when compared with those who did not live with two smoking parents).
The differences between those who stopped and those who did not are summarized in Tables II–III.
Since some of the factors showing correlation to stopping smoking were likely to be correlated also to each other, those giving significant results were tested by logistic regression. Few cigarettes smoked per day, combined with parental non-smoking, was associated with a higher likelihood of stopping smoking, while many cigarettes smoked per day by women with smoking parents was associated with less likelihood (Table IV).
The non-participants did not smoke more before the onset of pregnancy than those interviewed. However, they had stopped smoking less often when they first attended the ANC, compared with the participants at the interview (p<0.05). At week 32, the difference between the number of smokers in the two groups was not significant.
Discussion
The participants were all known smokers from the start, had agreed to participate and had been informed that an objective test for smoking would be performed. The CO test supported the data concerning smoking, both whether they had stopped or not and the average number of cigarettes smoked. Non-participants were found to have stopped smoking less often than participants at the first interview. However, the personal meeting took place a few weeks after the enlistment at the ANC and thus later in this group. This fact may explain the difference, since the advice given at the ANC may well have triggered the process of stopping smoking among the women. Since the difference was no longer significant at week 32, this suggests that the groups had similar smoking habits.
The overall figure for smoking at the participating ANCs in the present study was 18%, which is lower than in earlier studies (1, 2) but in line with recent figures from the National Birth Registry (3), suggesting a decline in smoking habits.
Age was not related to stopping smoking. This correlation was found in some previous studies during pregnancy (8) but not in others (9). As these investigations were made in different countries, with different cultural characteristics, comparisons are difficult.
It may be questioned whether it is fruitful to ask people about their parents’ smoking habits. Coultas et al. (10) found that adults can reliably report whether household members smoked during their childhood, although information on the quantitative aspects of smoking is less reliable.
Age, the smoking habits of the partner, exposure to passive smoking, quality of sleep, general perceived health, length of sick-leave or the amount of nausea during pregnancy showed no correlation to stopping smoking. It was more common, although not significantly, that the woman stopped smoking if her partner was not a smoker. Such a correlation has been described earlier (2). Do women these days act more independently than before and are they thus less influenced by the smoking habits of their partners? However, the partner can help the pregnant woman to stop even if he is a smoker himself. He should be informed about the importance of his support at the ANC. Positive support seems to be more effective in the process of stopping smoking than unconcern about or dislike of the woman’s smoking habit. Having started smoking at an older age, having no previous children, smoking fewer cigarettes, a higher level of education, positive support from the partner and not having lived with smoking parents were associated with stopping smoking when tested as single factors. Age at start of smoking and level of education were no longer significant when adjusted for other factors. If tested as the predicting factor against the others, age at start of smoking and level of education were related to more than one of the other factors, making the issue of causality complex. When planning the study, a mean difference in tested factors of 10% between those who stopped smoking and those who did not was anticipated and a sample of 100 participants should give power enough for significant results. This turned out to be true for several factors specially when tested univariately. Probably, however, the power of the study was not great enough to show differences reliably between subgroups in the material.
The use of mild cigarettes showed a poorer correlation to stopping smoking than fewer cigarettes smoked. This suggests that mild cigarettes do not help an addicted smoker very much to quit smoking. In addition, Frost et al. (11) found that advising people who have failed to give up smoking to switch to low-tar cigarettes reduces the intake of smoke constituents by only a small extent.
In the present study a correlation was found between the smoking habits of the parents and the woman’s tendency to stop smoking during pregnancy. Not only is a woman more likely to become a smoker herself if her parents smoke but she also seems to find it more difficult to stop during pregnancy and stops later if she succeeds. The reason for this is debatable. Kandel et al. (12) suggested that the smoke had an effect on the developing brain of the fetus. This early effect on the brain may perhaps also lead to increased difficulties in stopping smoking later in life. If this is the main reason for a future greater nicotine dependence, the smoking habits of the mother should be more important than those of the father. We did not find this difference and the fewest women stopped smoking if both parents had been smokers. A social pattern that regards smoking as something natural and undisputed in the family may explain why children in smoking families become smokers more often and are less motivated or less able to stop smoking. A recent study also emphasizes the early sensitivity to smells in the new-born child and its importance for future behavior (13). If the parents, who represent the greatest feeling of safety for the new-born child, and indeed also the breast milk (14), smell of tobacco, it is not surprising that the child will always retain a positive view of this smell, which may later make it harder for them to stop smoking. It may also be argued that the smoking habits of the parents are of no interest, since those habits could not be changed retrospectively. The reasons for helping pregnant women to stop smoking should be considered important enough to break the ‘heritage’ of the smoking habit and with it the related diseases. Even if this study shows that women with parents who smoke do not stop as often as the rest, many managed to do so, and are likely to benefit from well-planned, individualized support from the ANC.
