Smoking among pregnant women in Cantabria (Spain): trend and determinants of smoking cessation
© Palma et al; licensee BioMed Central Ltd. 2007
Received: 18 May 2006
Accepted: 27 April 2007
Published: 27 April 2007
Cantabria (Spain) has one of the highest prevalence of smoking among women of the European Union. The objectives are to assess the trend of smoking during pregnancy in a five-year period and the determinants of smoking cessation during pregnancy in Cantabria.
A 1/6 random sample of all women delivering at the reference hospital of the region for the period 1998–2002 was drawn, 1559 women. Information was obtained from personal interview, clinical chart, and prenatal care records. In the analysis relative risks and 95% confidence intervals were estimated. Multivariable analysis was carried out using stepwise logistic regression.
Smoking prior to pregnancy decreased from 53.6% in 1998 to 39.4% in 2002. A decrease in smoking cessation among women smoking at the beginning of pregnancy was observed, from 37.3% in 1998 to 20.6% in 2002. The mean number of cigarettes/day (cig/d) before pregnancy remained constant, around 16 cig/d, whereas a slight trend to increase over time was seen, from 7.7 to 8.9 cig/d. In univariate analysis two variables favoured significantly smoking cessation, although they were not included in the stepwise logistic regression analysis, a higher education level and to be married. The logistic regression model included five significant predictors (also significant in univariate analysis): intensity of smoking, number of previous pregnancies, partner's smoking status, calendar year of study period (these four variables favoured smoking continuation), and adequate prenatal care (which increased smoking cessation).
The frequency of smoking among pregnant women is very high in Cantabria. As smoking cessation rate has decreased over time, a change in prenatal care programme on smoking counseling is needed. Several determinants of smoking cessation, such as smoking before pregnancy and partner's smoking, should be also addressed by community programmes.
Cantabria, on the Cantabrian sea (northern Spain), has the highest frequency of smoking in Spanish women and one of the highest of the European Union, 35.6%, four points above the next area, the Basque region . This can imply a high prevalence of smoking during pregnancy in our region, although no data are available. Smoking cessation during pregnancy is strongly recommended because of the adverse effects of tobacco on the newborn [2, 3]. Reduction of smoking frequency among pregnant women has been reported in many countries [4–6], although the change during the last decade has been small in several areas . Nevertheless, some women continue smoking during pregnancy, despite counseling on stop smoking in prenatal care. The assessment of the determinants of smoking cessation can contribute to improve the efficacy of prenatal care programmes. The main objectives of this report are to analyse the evolution of smoking among pregnant women in a five-year period and to assess the determinants of smoking cessation in a European community.
The reference population was that of the region of Cantabria, northern Spain. The study period was from 1 April 1998 to 30 November 2002. Pregnant women were selected from those delivering at the University Hospital Marques de Valdecilla between 1 April 1998 and 30 November 2002 if they lived in Cantabria, the hospital's referral area. The hospital ethics committee authorised this observational study, and oral informed consent was sought from every eligible woman. During the study period, a random sample representing one-sixth of all women delivering at the hospital was drawn: all the women delivering on five days of each month, randomly selected in advance using the random number generator of a statistical program, were asked to participate. Twenty eight women declined to participate, yielding 1559 women in the study population.
The data were obtained from a personal interview, carried out within the three days after delivery, clinical charts and prenatal care records. We asked for tobacco consumption before and during pregnancy; all smokers before pregnancy continued smoking at the beginning of pregnancy (before they were aware of pregnancy). Therefore smoking prior to pregnancy and smoking at the beginning of pregnancy convey the same information. Information was obtained on the next variables: mother's vital data (age at pregnancy, race, education level, marital status, socioeconomic class, occupation), obstetric history (parity, abortions), previous adverse perinatal outcomes, conditions during pregnancy (infections, hypertension, diabetes mellitus, other obstetric conditions), prescribed and over-the-counter drugs, lifestyle (alcohol consumption, smoking), prenatal care (number of visits, date of first visit); and on the newborn (gestational age, anthropometric measures, Apgar score). Social class were coded in five main levels (ranging from I-highest- to V-lowest level-) according to the classification of the Spanish Society of Epidemiology , which is similar to the Black Report . Prenatal care utilization was measured using the Kessner index . This classification of prenatal care takes into account the month prenatal care began, the number of prenatal visits, and the duration of pregnancy; it differentiates three levels of care: adequate, intermediate, and inadequate.
In statistical analysis, the χ2 test was used to assess changes in categorical variables during the study period; if a variable was continuous one-way analysis of variance was applied. The Mantel-Haenszel extension of χ2 was used to ascertain the statistical significance of a trend for proportions. In bivariate analysis of smoking cessation, relative risks (RRs) and their 95% confidence intervals (CIs) were estimated; a RR > 1 indicates that a variable favours smoking cessation, whereas a RR < 1 denotes that a variable favours smoking continuation. To know the independent predictors smoking cessation, we developed a logistic regression model using a forward stepwise procedure. Variables with p-values lower than 15 percent were allowed in the final model. Analysis was carried out with the statistical package Stata 8/SE (College Station, Texas, USA).
Evolution for the study period of several population variables.
(n = 315)
(n = 316)
(n = 302)
(n = 306)
(n = 320)
Age in years, mean ± SD
28.6 ± 5.0
29.6 ± 5.3
29.9 ± 4.9
29.9 ± 4.5
30.1 ± 4.9
Primiparous, n (%)
Education higher than secondary school, n (%)
Married, n (%)
Employment out home, n (%)
Social class I-II, n (%)
Kessner index: adequate prenatal care, n (%)
Smokers prior to pregnancy, n (%)
No. cig/d, mean ± SD
14.5 ± 7.6
14.9 ± 8.7
15.9 ± 8.6
16.0 ± 8.9
Smoking during the whole pregnancy, n (%)
History of smoking during pregnancy in women smokers at the beginning of pregnancy.
History of smoking
(n = 169)
(n = 163)
(n = 132)
(n = 135)
(n = 126)
Cessation, n (%)
Continuing smoking, n (%)
c Reduction in smoking, n (%)
< 0.001 a
c No change or increase d, n (%)
No. cig/d, mean ± SD
7.7 ± 5.6
Variables related to smoking cessation during pregnancy (based on 725 women smoking at the beginning of pregnancy).
RR (95% CI)
High school education or higher
Marital status: married
No. of previous pregnancies
Employment outside home
Cig/d smoked before pregnancy
Change in alcohol consumption during pregnancy
Do not drink
Year of the study period
Independent variables related to smoking cessation yielded by logistic regression analysis.
OR (95% CI)
Cig/d smoked before pregnancy (continuous)
Kessner index (ref. inadequate):
Partner's smoking (ref. no)
No. of previous pregnancies (continuous)
Year of the study period (continuous)
We first comment on the limitations of the study. We have relied on the information given by women; their answers were not validated by cotinine measurements; therefore some degree of misclassification must be assumed. In a Spanish study, the proportion of pregnant non-smokers with negative urine cotinine (negative predictive value) was 82.9% . This proportion is lower than that found in an American study . where 94.9% of women who denied smoking yielded no urine cotinine. In general, it is believed that pregnant women accurately report tobacco smoking, although some under-declaration occurs [11, 12]. There is no reason to believe that misclassification bias changed during the study period, so we believe that our results on the evolution of smoking in our region are reliable.
Our results agree with the decreasing frequency of smoking in women reported in Europe ; nevertheless, our data confirm a high prevalence of smoking among women of childbearing ages, almost 40% in 2002. The prevalence of smoking among pregnant women in Cantabria, above 30% throughout the quinquennial period 1998–2002, is one of the highest in the Western world; for instance, this figure was 21.8% in Sweden in 1992 , 21.2% in Finland in 1990 , 11.8% in the US in 1996 , and 4.4% in Czech Republic in 1997 .
The decreased frequency of smoking during pregnancy observed in Cantabria, 16.7% from 1998 to 2002, is higher than that found in other countries. In Sweden from 1983 to 1992 this figure was 7.6% , and 4.5% from 1987 to 1996 in the US  (although most of this decrease was observed for the period 1987–1990) . The mean number of cigarettes/day smoked by pregnant women in Cantabria shows a slight trend to increase, although this amount is lower than the US figure, 10 cigarettes/day .
Our data show that the decline in smoking among pregnant women from 1998 to 2002 in Cantabria was primarily due to the overall decrease in smoking before pregnancy, not to an increased rate of smoking cessation in pregnancy; this has also been reported in the US . Our figure of smoking cessation is lower than that found in other Spanish report, where 46.9% of smokers quit tobacco in pregnancy .
Regarding the determinants of smoking cessation, one of the most important factors is the intensity of habit at the beginning of pregnancy, being heavy smokers more reluctant to quit smoking [6, 16–22]. Other predictor of smoking cessation frequently reported is partner's smoking status [17–19, 21, 23]. We also found this relationship in the multivariable model.
Primiparous women quit smoking more frequently than multiparous [23–27]. This is also supported in our data, where an inverse linear relationship between the number of previous pregnancies and smoking cessation has been observed.
In the US white race has been found a strong predictor of smoking in pregnancy [5, 21, 26–28]. In our sample the number of non-white women is small, thus we lack statistical power to draw any significant conclusion.
A high education level is negatively related with smoking [5, 19, 21–23, 29], not found in one report . In our data, a high education level increased smoking cessation in crude analysis, although this variable lost its statistical significance in multivariable analysis. Social class was unrelated to smoking cessation; in Denmark, this variable exerted only a small effect on cessation . Married women showed a higher smoking cessation rate, but it lost its influence in multivariable analysis. This agrees with the results reported in other study .
We have only found one report relating adequacy of prenatal care to smoking cessation , women attending prenatal care in the first trimester quit smoking more successfully. This agrees with our results, women receiving adequate prenatal care (which by definition begins in the first trimester) show a higher rate of smoking cessation. This may also be due to personal characteristics of women: those prone to quit smoking attended more to prenatal care.
Some of the variables related to smoking cessation are not amenable by a prenatal care programme and need to be addressed by community programmes on quit smoking; this occurs with smoking before pregnancy or partner's smoking. We included in multivariable analysis the year of the study period, as a decline in smoking cessation along the study period was observed in bivariate analysis. This was done to ascertain whether other variables could take this influence into account. The effect of the year of study period remained highly significant in the multivariable model. It is important to remark that prenatal care improved considerably in Cantabria from 1998 to 2002. This was accompanied with a lower cessation rate. In Cantabria it is established in the written program of prenatal care to give advice on smoking cessation, but "how" to counsel is not detailed. In general, Spanish physicians are not trained in health education; this means that intervention on smoking cessation is low. To achieve changes in smoking behaviour among pregnant women with low-intensity interventions integrated into routine prenatal care is difficult . It is assumed that counseling on smoking cessation did not change during the study period, what implies that Cantabrian pregnant women at the beinning of the 2000s are more reluctant to quit smoking than previously. This emphasizes the need to change the strategy of addressing smoking cessation in our region. Two systematic reviews have established the efficacy of smoking cessation programmes [31, 32]; the following interventions are effective: a brief cessation counseling session of 5–15 minutes delivered by a trained provider, plus the provision of pregnancy specific, self help materials , or the Agency for Health Care Policy and Research guideline recommendations on smoking cessation .
In Cantabria (Spain) a high frequency of smoking during pregnancy has been found, associated to both a decreasing smoking cessation and an improvement of prenatal care over time. These latter facts imply the need for a different approach (within prenatal care) of health education against tobacco smoking in Cantabria. Other variables, such as previous pregnancies or marital status, cannot been managed by prenatal care programmes. Several determinants of smoking cessation (smoking prior to pregnancy, partner's smoking status) need to be addressed by community programmes.
List of abbreviations
This work has been funded by the Andalusian Regional Ministry of Education & Science (CTS 435) and research funds provided by the Foundation Marqués de Valdecilla of Santander (University of Cantabria).
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