Prevalence of smoking during pregnancy and associated risk factors among Canadian women: a national survey.

Abstract

Cigarette smoking carries a threat both to the expecting mother and her newborn. Data on the prevalence and predictors of smoking during pregnancy is limited in Canada. Canadian studies are mainly representative of specific cities and/or provinces. Therefore, the study aims to assess the prevalence of smoking during pregnancy and its associated risk factors throughout the Canadian provinces and territories.
The analysis was based on the Maternity Experience Survey targeting women aged > or =15 years who had singleton live births during 2005/06 in the Canadian provinces and territories. The outcome was ever smoking during the thirst trimester of pregnancy. Socio-economic factors, demographic factors, maternal characteristics, and pregnancy related factors that proved to be significant at the bivariate level were considered for a logistic regression analysis. Bootstrapping was performed to account for the complex sampling design.
The sample size was 6,421 weighted to represent 76,508 Canadian women. The prevalence of smoking during pregnancy was 10.5%, whereby smoking mothers consumed on average 7 cigarettes a day (95% Confidence interval - CI: 6.5-7.4; SD = 5.7). Regression analysis revealed that mothers who smoked during pregnancy were more likely to be of low socio-economic status, non-immigrant, single and passive smokers during pregnancy. Not attending prenatal classes and experiencing stressful events before/during pregnancy also increased the mothers' odds of smoking during pregnancy. While the age of the mother's first pregnancy was negatively associated with smoking during pregnancy, the mother's current age was positively associated with it.
Smoking during pregnancy is still prevalent among Canadian women. The findings may be useful to enhance smoking prevention programs and integrated health promotion strategies to promote positive health behaviors among disadvantaged pregnancies.

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Al-Sahab et al. BMC Pregnancy and Childbirth 2010, 10:24
http://www.biomedcentral.com/1471-2393/10/24
Open Access
RESEARCH ARTICLE
Prevalence of smoking during pregnancy and
associated risk factors among Canadian women: a
national survey
BioMed Central
© 2010 Al-Sahab et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons
Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in
any medium, provided the original work is properly cited.
Research article
Ban Al-Sahab*, Masarat Saqib, Gabriel Hauser and Hala Tamim
Abstract
Background: Cigarette smoking carries a threat both to the expecting mother and her newborn. Data on the
prevalence and predictors of smoking during pregnancy is limited in Canada. Canadian studies are mainly
representative of specific cities and/or provinces. Therefore, the study aims to assess the prevalence of smoking during
pregnancy and its associated risk factors throughout the Canadian provinces and territories.
Methods: The analysis was based on the Maternity Experience Survey targeting women aged ≥15 years who had
singleton live births during 2005/06 in the Canadian provinces and territories. The outcome was ever smoking during
the thirst trimester of pregnancy. Socio-economic factors, demographic factors, maternal characteristics, and
pregnancy related factors that proved to be significant at the bivariate level were considered for a logistic regression
analysis. Bootstrapping was performed to account for the complex sampling design.
Results: The sample size was 6,421 weighted to represent 76,508 Canadian women. The prevalence of smoking during
pregnancy was 10.5%, whereby smoking mothers consumed on average 7 cigarettes a day (95% Confidence interval -
CI: 6.5-7.4; SD = 5.7). Regression analysis revealed that mothers who smoked during pregnancy were more likely to be
of low socio-economic status, non-immigrant, single and passive smokers during pregnancy. Not attending prenatal
classes and experiencing stressful events before/during pregnancy also increased the mothers' odds of smoking
during pregnancy. While the age of the mother's first pregnancy was negatively associated with smoking during
pregnancy, the mother's current age was positively associated with it.
Conclusion: Smoking during pregnancy is still prevalent among Canadian women. The findings may be useful to
enhance smoking prevention programs and integrated health promotion strategies to promote positive health
behaviors among disadvantaged pregnancies.
Background
Cigarette smoking carries a threat both to the expecting
mother and her newborn. Tobacco products are responsi-
ble for many complications including tobacco-induced
abortions, deaths from perinatal disorders [1], newborns
requiring admission to neonatal intensive care unit [2],
low-birth weight infants [3], and deaths from Sudden
Infant Death Syndrome [4]. Furthermore, cigarette smok-
ing increases the risk of infertility and conception delay
[5], as well as harmful pregnancy outcomes, such as pre-
mature rupture of membranes [6], placenta previa [7],
abruptio placenta [8], stillbirth [4], and preterm delivery
[9].
The prevalence of smoking among pregnant women
has been shown to vary across different countries. For
example, prevalence rates range from 9.9% in Japan [10],
to 17% in Australia [11], to 30-35% in Spain [12]. In Can-
ada, the prevalence of smoking among pregnant women
was estimated to be 17% in 2000/01 [13]. During the same
period, however, a study conducted in three Southern
Ontario Health Units revealed that 10.4% of the women
smoked at some point during their pregnancy [14]. Data
taken from 1999-2000 revealed that, in Winnipeg, 26.2%
of non-aboriginal and 61.2% of aboriginal women smoked
after being aware of their pregnancy [15]. From 1998-
* Correspondence: bsahab@yorku.ca
1 School of Kinesiology and Health Science, York University, Toronto, ON
Canada M3J 1P3
Full list of author information is available at the end of the article

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2001, the overall prevalence of smoking just before deliv-
ery in Nova Scotia was 25.1% [16].
Internationally, predictors of smoking among pregnant
women have been well investigated. Studies found that
age, education, ethnicity, martial status, alcohol con-
sumption, work status, and the mother's reproductive
history are associated with smoking during pregnancy
[11,17-19]. In Canada, pregnant smokers were more
likely to be under 25 years of age [14], to have lower
income levels [20], to be unmarried [20] and to have oth-
ers in the household who smoked [21]. Moreover, Cana-
dian women who were pregnant with their first child and
who consumed alcohol during their pregnancy were also
more likely to relapse to smoking during pregnancy [22].
Despite the well known and detrimental effects of
smoking, it remains prevalent among pregnant women.
In order to determine the groups of women that are at
higher risk of smoking and to tailor appropriate interven-
tions, the identification of prevalence and predictors is
crucial. Data on the prevalence and predictors of smoking
during pregnancy, however, is limited in Canada. Cana-
dian studies are mainly representative of specific cities
and/or provinces [14,15,20,21,23-30]. To our knowledge,
only two studies assessed smoking during pregnancy at
the national level [13,22]. The study by Connor & McIn-
tyre (1999) used 1994 data from the National Longitudi-
nal Child and Youth Survey, whereby the unit of analysis
is the child and not the mother [22]. Millar & Hill (2004),
on the other hand, based the analysis on the 2000/01
Canadian Community Health Survey [13]. Smoking dur-
ing pregnancy, however, was assessed within 5 years in
the past, which increases the chance of recall bias. Both
national studies excluded mothers in the northern terri-
tories and investigated limited demographic and socio-
economic predictors. The present study, however, uses
data from a recent specialized survey on pre and post
delivery experiences among mothers residing in both the
Canadian provinces and the territories. It aims to exam-
ine and assess the prevalence of smoking during preg-
nancy and the potential socio-economic, demographic
maternal and pregnancy related risk factors.
Methods
The analysis of this study is based on the Maternity Expe-
rience Survey (MES) that was sponsored by Public Health
Agency of Canada and conducted by Statistics Canada in
2006. The MES study is a nationwide survey that assessed
pregnancy, delivery and postnatal experiences of mothers
and their children. Participants eligible for the study were
women aged 15 years and above, who had singleton live
births between the period of February 15, 2006 and May
15, 2006 in the provinces of Canada and between Novem-
ber 1, 2005 and February 1, 2006 in the territories of Can-
ada and who lived with their baby at the time of data
collection. A stratified random sample of 8,542 Canadian
women was selected without replacement from the 2006
Canadian Census of Population. Around 8,244 women
were estimated to have met the eligibility criteria of the
study. A total of 6,421 women, however, responded to the
survey. Non-response to the survey was mainly from
inability to establish contact with the mothers. Prior to
data collection, an introductory letter and survey pam-
phlet were mailed to the women and invited them to par-
ticipate in the survey. Then the data was collected
through telephone interviews using a computer-assisted
telephone interview application. In an attempt to recruit
the highest number of mothers possible, a total of 25 calls
per each case were made during different days of the
week and different hours of the day. The MES question-
naire was also available in 15 languages. Majority of the
interviews were conducted between the 5th and 9th month
after delivery and lasted on average 45 minutes. The MES
project was presented to Health Canada's Science Advi-
sory Board, Health Canada's Research Ethics Board and
the Federal Privacy Commissioner and was approved by
Statistics Canada's Policy Committee. The study has been
previously described in other references [31,32].
The main outcome of the study is smoking during preg-
nancy defined as ever smoking during the last three
months of pregnancy. This variable was measured based
on the question "During the last 3 months of your preg-
nancy, did you smoke daily, occasionally, or not at all?"
Daily and occasional respondents were grouped as ever
smokers. Other considered smoking related variables
were smoking before pregnancy assessed by the question
"In the three months before your pregnancy, or before
you realized you were pregnant, did you smoke daily,
occasionally or not at all?" and smoking after pregnancy
measured by the question "At the present time, do you
smoke cigarettes daily, occasionally or not at all?". The
response categories for both questions were daily, occa-
sionally and not at all. Similar to smoking during preg-
nancy, daily and occasional respondents were grouped as
smokers. The number of cigarettes smoked was also con-
sidered. For daily users, the question was: "How many
cigarettes do you smoke each day?". For occasional smok-
ers, on the other hand, it was: "On the days that you do
smoke, how many cigarettes do you usually smoke?".
A wide range of independent variables were investi-
gated as potential predictors of smoking during preg-
nancy. These variables were: i) socio-economic factors:
maternal years of education, total household income,
maternal work status during pregnancy and place of resi-
dence (urban vs. rural); ii) demographic factors: immigra-
tion status and province of residence; iii) maternal
characteristics: marital status, age at first pregnancy,
number of previous pregnancies, age at selected birth,
and mother's perceived health; and iv) pregnancy related

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factors: self reported weight gain during pregnancy, alco-
hol drinking during pregnancy, support during preg-
nancy, mother's reaction to pregnancy, mother's stress
level before and during pregnancy, health problems dur-
ing pregnancy (defined as any new medical conditions or
health problems that required taking medication for
more than 2 weeks, having special care, or extra tests),
passive smoking during pregnancy (defined as ever living
with someone who smoked at any point during the
mother's pregnancy), attendance of prenatal or childbirth
education classes during the pregnancy and the number
of times the pregnant women have visited a health care
provider during the pregnancy. All the variables, except
for mother's stress level, were directly self-reported by
the mother. The mother's stress level, however, was mea-
sured through a set of 13 questions that examined the
mother's experience of 13 specific stressful events in the
past 12 months before the birth of her selected child. The
answers for these questions were categorised as "Yes" or
"No". Consequently, the sum of the "Yes" responses was
calculated for each mother to represent the number of
stressful events experienced [32]. The stress questions
were adapted by Pregnancy Risk Assessment Monitoring
System from the Life Events Inventory that was devel-
oped by Newton and Hunt [33]. For more information,
the MES questionnaire is available online [34].
The prevalence of smoking was estimated through pop-
ulation weights and examined across all the Canadian
provinces and territories. Population weights estimate
the number of people not selected in the sample that have
been represented by each person in the sample. It also
takes into consideration non-response in the survey [32].
At the bivariate level, differences in the proportion of
smokers was assessed among the different levels of each
predictor using normalized weights. Odds ratios (OR)
using 95% confidence intervals (95% CI) were performed
for categorical variables. Differences in means with 95%
confidence interval estimations, on the other hand, were
employed for continuous variables. Factors that proved to
be significant at the bivariate level were considered for a
multivariate logistic regression analysis. Adjusted OR and
95% CI were reported for the final model. To account for
the complex sampling design, bootstrapping was per-
formed to calculate all the 95% CI estimates [35,36]. Pop-
ulation weights, normalized weights and bootstrap
weights were all created by Statistics Canada and pro-
vided with the MES data file. All analyses, in exception to
bootstrapping, were conducted using the Statistical Pack-
age for Social Sciences (SPSS, version 16.0). Bootstrap-
ping was performed using the Statistical Analysis
Software (SAS, version 9.2).
Results
The sample size for the population analyzed in this study
was 6,421 weighted to represent 76,508 Canadian
women. Table 1 presents the estimated population and
distribution of smoking practices before, during and after
pregnancy. The proportion of women who smoked
before, pregnancy was 22.0%, while it was 16.5% after
pregnancy. The prevalence of smoking during pregnancy,
however, was 10.5% (6.9% daily smokers and 3.6% occa-
sional smokers). Women who smoked during pregnancy
consumed on average a total of 7 cigarettes a day (95% CI:
6.5-7.4; SD = 5.7), whereby daily users smoked on average
9 cigarettes (95% CI: 8.4-9.5; SD = 5.9) and occasional
users smoked on average 3 cigarettes (95% CI: 2.9-3.5; SD
= 2.5). Most regions in Canada displayed relatively similar
smoking rates during pregnancy except for the Northern
Territories (39.4%) and Prince Edward Island (20.8%)
(Figure 1). The prevalence of smoking, on the other hand,
was least prevalent in British Columbia (8.5%) and
Ontario (8.8%).
Unadjusted and adjusted associations between smoking
during pregnancy and potential factors are illustrated in
Table 2. All variables significant at the bivariate level were
considered for a logistic regression model. Out of the 18
significant variables at the bivariate level, 10 remained
significant in the final model. Income, place of residence
Table 1: Distribution of smoking before, during and after pregnancy among Canadian mothers (2005/06).
N*% (95% CI)†
Smoking before pregnancy 16,823 22.0 (21.1-23.0)
Smoking after pregnancy12,63416.5 (15.7-17.4)
Smoking during pregnancy8,01510.5 (9.8-11.2)
Smoking during pregnancy frequency
Daily5,253 6.9 (6.3-7.5)
Occasionally2,7623.6 (3.2-4.1)
Never68,31989.5 (88.8-90.2)
* Sample size is estimated using population weights
† 95% CI were calculated using bootstrapping technique

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and years of education, that are considered to be indica-
tors of socio-economic status, were negatively associated
with smoking during pregnancy. Mothers who had the
lowest household income (<$30,000 and $30,000 to less
than $60,000) were more likely to smoke during preg-
nancy (OR: 1.73, 95% CI: 1.08-2.78 and OR: 1.86, 95% CI:
1.21-2.85, respectively) than women with higher income.
Similarly, women who lived in rural and semi-urban areas
had higher odds of smoking in their pregnancy. In addi-
tion to socio-economic status, marital status was found
be significantly associated with smoking during preg-
nancy, whereby single mothers were more prone to
smoking. Although old mothers were more likely to be
smokers, mothers who had their first pregnancy at a
young age were also at an increased risk of smoking dur-
ing pregnancy. Moreover, non-immigrant mothers and
passive smokers were almost 5 times more likely to
smoke during their pregnancy as compared to their coun-
terparts (95% CI: 3.32-8.51 and 95% CI: 4.28-6.58, respec-
tively). Finally, the failure to attend prenatal classes and
experiencing stressful events were found to be associated
with smoking during pregnancy. The odds ratio of not
attending prenatal classes was 1.43 (95% CI: 1.10-1.86),
while it was 1.15 for experiencing stressful events (95%
CI: 1.08-1.23).
Discussion
The present study aimed to assess the prevalence and
characteristics of smoking during pregnancy among
Canadian women. Results showed that the prevalence of
smoking at any time in the third trimester was 10.5%, and
that the average daily consumption of cigarettes was
around 7 (95% CI: 6.5-7.4; SD = 5.7). Regression analysis
revealed that mothers who smoked during pregnancy
were at greater odds for being of low socio-economic sta-
tus, non-immigrant, single and exposed to passive smok-
ing during pregnancy. Not attending prenatal classes and
experiencing stressful events before and during preg-
nancy also increased the mothers' odds of smoking dur-
ing pregnancy. While the age of the mother's first
pregnancy was negatively associated with smoking dur-
ing pregnancy, the mother's current age was positively
associated with it.
The prevalence of smoking during pregnancy is compa-
rable with other modern industrialized nations. A recent
American study reported that the smoking rate is 10%
[37], while another study from Germany assessed the rate
as 13% [38]. The present study's smoking rate, however, is
lower than the previous two national Canadian studies
[13,22]. Connor & McIntyre (1999) determined the prev-
alence rate of smoking during pregnancy in 1994 as 23.7%
and Millar & Hill (2004) evaluated it as 17% in 2000/01.
The provincial prevalence rates of the present study are
also lower than those reported by Millar & Hill (2004). In
Newfoundland and Labrador, for example, the rate was
previously described as 26% while it was revealed to be
10.6% in the present study. Similarly, the rate dropped
from 17% to 13.8% in Nova Scotia, from 21% to 10.9% in
Figure 1 Distribution of smoking during pregnancy across the Canadian provinces and territories (2005/06).

10.60%
20.80%
13.80%
13.60%
10.90%
8.80%
14.60%
16.20%
11.80%
8.50%
39.40%
Prince Edward Island
Nova Scotia
New Brunswick
Quebec
Ontario
Manitoba
Saskatchewan
Alberta
British Columbia
Northern territories
Canada (10.5%)
Newfoundland and Labrador

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Table 2: Unadjusted and adjusted associations between smoking during pregnancy and potential predictors.
Sample size Smoking during
pregnancy
Unadjusted odds
ratio
Adjusted odds ratio
N*N*(%)OR (95% CI)†OR (95% CI) †
Household income
< $30,0001,031230 (22.3)
10.12 (6.77-15.13) 1.73 (1.08-2.78)
$30,000 to less
than $60,000
1,853 242 (13.1)
5.31 (3.54-7.95)1.86 (1.21-2.85)
$60,000 to less
than $100,000
1,940111 (5.7)
2.14 (1.39-3.30)
1.09 (0.71-1.69)
≥ $100,0001,212 33 (2.7)11
Place of residence
Rural area 1,100 150 (13.6)
2.23 (1.78-2.80) 1.40 (1.04-1.87)
Urban, population
≤ 499,999
2,283 310 (13.6)
2.22 (1.81-2.72)1.42 (1.10-1.82)
Urban, population
≥ 500,000
2,791 185 (6.6)11
Immigrant
No4,980 641 (12.9)
7.26 (4.79-11.00)5.32 (3.32-8.51)
Yes1,407 28 (2.0)11
Work during
pregnancy
No 1,364195 (14.3)
1.60 (1.34-1.91)
0.93 (0.72-1.20)
Yes5,028 475 (9.4)11
Marital status
No partner535168 (31.4)
4.88 (3.97-6.01) 1.83 (1.33-2.53)
Have a partner5,860501 (8.5)11
Moms perceived
health
Excellent/very
good
4,645396 (8.5)11
Good1,419208 (14.7)
1.84 (1.53-2.21)
1.17 (0.92-1.49)
Poor/Fair34169 (20.2)
2.70 (2.03-3.60)
1.01 (0.67-1.51)
Alcohol drinking
during pregnancy
No5,713 576 (10.1)11
Yes66989 (13.3)
1.36 (1.06-1.74)
1.28 (0.93-1.77)
Health problems
during pregnancy
No4,837485 (10.0)11
Yes 1,563 186 (11.9)
1.21 (1.01-1.46)
1.19 (0.95-1.50)
Reaction when
discovered pregnancy
Very happy/happy5,940 576 (9.7)11
Indifferent 26558 (21.9)
2.63 (1.94-3.56)
1.09 (0.71-1.69)
Very unhappy/
Unhappy
18036 (20.0)2.35 (1.60-3.46)0.93 (0.54-1.61)