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| Journal of the New Zealand Medical Association,
26-November-2004, Vol 117 No 1206
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Smoking among mothers of a Pacific Island birth cohort in New
Zealand: associated factors
Sarnia Butler, Maynard Williams, Janis Paterson, Colin
Tukuitonga
Cigarette smoking has been linked to serious health problems
including respiratory infections, asthma, cardiovascular disease, psychiatric
disorders, cancer, and death.1 For women,
smoking carries the additional increased risk to reproductive health of reduced
fertility, early menopause, ectopic pregnancy, osteoporosis, cervical cancer,
infants of low birth weight, and
stillbirth2,3—risks which many women are
unaware of.3
Smoking during pregnancy has been linked to a high
prevalence of delivery complications and morbidity for both mothers and
infants,1,4 with numerous adverse health
consequences beyond birth for children including increased risk of sudden infant
death syndrome,5 respiratory
illness,6 and hospitalisation with infectious
diseases.7 Taken together, these studies
reinforce the need to reduce tobacco use, particularly during pregnancy.
To better inform smoking cessation programmes, factors that
characterise women who smoke during pregnancy need to be identified. Smoking
during pregnancy has frequently been associated with markers of socioeconomic
disadvantage such as unemployment,2,8 low
education,2,9–11 low
income,12,13 single marital
status,8–10 rental housing
tenure,2 and younger maternal
age.9,10,14
The American Academy of Pediatrics Committee on Substance
Abuse has suggested that there is a need for information regarding tobacco use
by different ethnic groups to guide understanding of different smoking patterns,
to aid in the development of culturally appropriate interventions, and to
evaluate their efficacy.1
While not specific to pregnancy, data from the 1996 New
Zealand Census indicated that the prevalence of smoking for women is cause for
concern with approximately 25% of European, 27% of Pacific, and 50% of Maori
women aged 15–49 years reporting to be
smokers.15
As little is known about smoking behaviour during pregnancy
among Pacific women in New Zealand, the aim of the present study was to
investigate the rates of smoking before, during, and after pregnancy—and
to identify factors predictive of smoking during pregnancy among mothers of a
birth cohort of Pacific infants.
MethodData were collected as part of
the Pacific Islands Families (PIF) Study, a longitudinal investigation of a
cohort of 1398 infants (11 pairs of twins) born at Middlemore Hospital, South
Auckland, New Zealand during the year 2000. Middlemore Hospital was chosen as
the site for recruitment of the cohort as it has the largest number of Pacific
births in New Zealand and is representative of the major Pacific ethnicities.
It was estimated that a cohort of 1000 would provide
sufficient statistical power to detect moderate to large differences after
stratification for major Pacific ethnic groups and other key variables.
Eligibility criteria included having at least one parent who self-identified as
being of Pacific ethnicity and a New Zealand permanent resident. Thus,
non-Pacific mothers were eligible for the study in cases where the
infant’s father was of Pacific descent. Detailed information about the
cohort and procedures is described elsewhere.16
Approximately 6 weeks after the birth of their child,
Pacific interviewers, who were fluent in English and a Pacific language, visited
the mothers in their homes. Of the 1376 mothers, 1365 were biological and 11
were foster or adoptive mothers. Eligibility criteria were confirmed and
informed consent was gained for participation in an interview and access to
their Middlemore Hospital discharge record.
Mothers participated in 1-hour interviews in their
preferred language concerning the health and development of the child and family
functioning. As part of this interview, mothers approximated how many cigarettes
they had smoked per day before pregnancy and during the three trimesters of
pregnancy. Current smoking behaviour was measured by the number of cigarettes
smoked yesterday (the day before the interview).
Data collected on a number of sociodemographic and
pregnancy-related factors were double-entered into the statistical software
package SPSS (version 11.5.1). Univariate and multivariate logistic regression
procedures were employed to examine association between these factors and risk
of smoking during pregnancy. Responses based on the first-born twin for twin
pairs were utilised in all analyses.
Variables examined included age, whether born in New
Zealand, marital status, ethnicity (self-identified), education, English fluency
(self-categorised), years in New Zealand, household income, housing tenure,
parity, other smokers in the home, whether pregnancy was planned, and attendance
at antenatal classes.
Cultural alignment was measured with an adaptation of
the short version of the General Ethnicity
Questionnaire17 which categorises a
person’s alignment as either ‘high’ or ‘low’
towards mainstream New Zealand way of life and customs in addition to being
either ‘high’ or ‘low’ towards the Pacific way of life
and customs.
In the analyses, mothers were considered employed if
they reported being in any paid employment (part, full, or self
employment).
ResultsNinety-six percent (N=1590) of
potentially eligible mothers of Pacific infants who had been born between 15
March 2000 and 17 December 2000, gave consent to be visited in their homes when
the infant was 6 weeks old. Of the 1477 mothers contacted and who met the
eligibility criteria, 1376 (93.2%) agreed to participate in the study. A more
conservative recruitment rate of 87.1% would include mothers who consented to
contact and were (a) confirmed eligible, or (b) of indeterminable eligibility
due to inability to trace.
Of the 1365 biological mothers in the present study (1.7%
gave birth to twins; n=23), 47.3% self-identified their major ethnic group as
Samoan, 16.7% as Cook Island Maori, 4.3% as Niuean, 21.0% as Tongan, 3.4% as
Other Pacific (includes mothers identifying equally with two or more Pacific
groups, equally with Pacific and Non-Pacific groups or with Pacific groups other
than Tongan, Samoan, Cook Island Maori, or Niuean), and 7.3% as Non-Pacific. The
mean (SD) age of mothers was 27.8 (6.1) years; 80.4% were living together in
married or defacto partnerships, 33.0% of mothers were New Zealand born, and
27.5% had post-school qualifications.
Table 1 gives the number and proportion of women who smoked
before pregnancy, during each of the three trimesters of pregnancy, at any time
during pregnancy, and yesterday (current smokers). Of the 435 smokers before
pregnancy, 331 (76.1%) continued to smoke during pregnancy. McNemar Chi-squared
tests (p<0.001) showed a significant reduction in the number of smokers from
before pregnancy to the period during pregnancy. Eight mothers who reported not
smoking before pregnancy commenced smoking during their pregnancies.
Table 1. Numbers (N) of Pacific mothers smoking before,
during, and after pregnancy (N=1364)
Table 2 shows the number of cigarettes consumed daily before
and during the three trimesters of pregnancy. Selecting those mothers who smoked
both before pregnancy and during the first trimester, and grouping cigarette
doses into light (1–9) and moderate/heavy (10 or more), McNemar
Chi-squared tests (p<0.001) showed that there was a significant reduction in
the percentage of moderate/heavy smokers once pregnant.
Similarly, tests comparing the third and first trimesters
revealed a significant (p<0.001) reduction in proportion of moderate/heavy
smokers from the first to the third trimester. Thus, the majority of
moderate/heavy smokers continued to reduce their daily cigarette intake
throughout pregnancy.
Table 2. Mean daily cigarette dose smoked by the sample
of Pacific mothers before, during, and after pregnancy
Table 3 lists variables examined for potential association
with smoking during pregnancy. For the categories within each variable the
numbers and percentages of mothers who reported smoking are given along with
their respective univariate odds ratio (95% CI) indicating likelihood of smoking
during pregnancy.
Table 3: Numbers (row percentages) and Univariate Odds
Ratios of smoking during pregnancy by selected variables (N=1365)
NZ=New Zealand; *p<0.05; †p<0.01;
‡p<0.001; §Includes mothers identifying equally with two or more
Pacific Island groups, equally with Pacific Island and non-Pacific Island
groups, or with Pacific Island groups other than Tongan, Samoan, Cook Island
Maori, or Niuean.
A multiple logistic regression analysis was undertaken to
control for potential confounding effects. Five demographic variables (maternal
age, education, ethnicity, marital status and household income) were initially
forced into the model as control variables and then all remaining variables in
Table 3 were then submitted to a forward stepwise procedure (p to enter=0.15 and
p to remove =0.20).
Table 4 demonstrates that when adjusting for all other
variables in the final model, factors which were significantly associated with
smoking during pregnancy (p<0.05) were not being in a married or defacto
relationship, being of Niuean, ‘Other Pacific’ or Non-Pacific
ethnicity, being fluent in English and residing in New Zealand for more than 10
years, a parity of two or more children, not attending antenatal classes, and
living with other smokers during pregnancy. Compared to no formal educational
qualifications, having secondary school qualifications reduced likelihood of
smoking during pregnancy (p<0.05).
Table 4. Adjusted odds of smoking during pregnancy for
variables attaining significance|| in a
multiple logistic regression (n=1328)
*p<0.05; †p<0.01;
‡p<0.001; §Includes mothers identifying equally with two or more
Pacific Island groups, equally with Pacific Island and non Pacific Island
groups, or with Pacific Island groups other than Tongan, Samoan, Cook Island
Maori, or Niuean; ||Factors included in the
final model but not reaching significance were maternal age and household
income.
DiscussionThe present study shows that
smoking, particularly during pregnancy, continues to be a substantial public
health problem requiring greater attention. 435 (31.9%) mothers reported smoking
before pregnancy, 339 (24.9%) mothers reported smoking during pregnancy, and by
6-weeks post-birth, 342 (25.1%) mothers reported that they were current smokers.
The proportion of pre-pregnancy smokers in the study was slightly higher than
the 27% recorded nationally for Pacific women in the 1996
Census.18
In concordance with a recent New Zealand
study,13 and in contrast to others who reported
36%–46% of smokers ceased smoking during
pregnancy,10,19 less than a quarter of smoking
women in our study stopped during their pregnancy and a small number even
started smoking at this time.
The rate of smoking during pregnancy recorded in our study
was higher than some recent international comparisions of
11%–16%,14,19,20 but in line with those
reporting the prevalence of maternal smoking to be in the 20%–30%
range,10,11 including New Zealand research
conducted approximately 10 years ago in which 23.6% of Pacific mothers smoked
during pregnancy compared with 33.2% for the whole population
sampled.9 In addition, inspection of smoking
rates by trimester show similarities to that reported in a 1997 Christchurch
study.21
In the present study, 23.7% smoked in the first, 21.0% in
the second, and 20.4% in the third trimester of pregnancy. Smoking rates for the
Christchurch study were 26.8%, 25.0%, and 23.0% for the first, second and third
trimesters, respectively.21 While small
fluctuations over time have been observed, the smoking rates during pregnancy
have remained fairly stable at approximately 30% for 20
years.22
Heavy smoking has been classified as smoking over 10
cigarettes3, 9 or in some studies, over 20
cigarettes daily.12,19,20 Examination of
cigarette consumption in the present study showed (overall) 48.3% of smokers
consumed more than 10 cigarettes daily before pregnancy, signifying an almost
even split between light smokers (1–9 cigarettes per day) and
moderate-to-heavy smokers (10> cigarettes per day) among Pacific women.
However, by the third trimester, a reduction in numbers of
heavy smokers was observed with 30.2% of smokers consuming over 10 cigarettes
daily. These figures are similar to those observed in the New Zealand Plunket
National Child Health Study, where Pacific mothers were considered lighter
smokers than other ethnic groups with only 36% of Pacific mothers smoking more
than 10 cigarettes daily compared to 71% of Maori
mothers.9
Overall, mothers reduced tobacco intake once pregnant.
Whether this was due to a conscious decision to reduce harm to the foetus or for
other reasons is not known. Other researchers have also found that mothers tend
to reduce their cigarette intake once
pregnant12,23 but significant numbers of
mothers subsequently relapse in the months following
birth.12 Nevertheless, unlike complete
cessation, reducing cigarette smoking may not eliminate all risks to the
infant.24
After controlling for confounding factors, two markers of
socioeconomic disadvantage (non-partnered marital status and low education) were
significantly associated with smoking during pregnancy. These findings provide
some support for the suggestion that smoking is associated with socioeconomic
determinants of health, that smokers are a high-risk group from multiple
perspectives,14 and that smoking may be a
coping mechanism for stressful life
circumstances.10
In line with earlier
research,8-10,14 not being partnered (not
married or in a defacto relationship) increased the odds of being a maternal
smoker compared to being partnered. As identified
previously,2,9,10 those with no formal
educational qualifications were more likely to be smokers than those with
secondary school qualifications. Low education may be a reflection of inferior
knowledge regarding the deleterious consequences of smoking during
pregnancy.11
In contrast to others,8,12
multivariate analyses showed that household income and employment status did not
exert any independent influence on smoking status. Similarly, no independent
influence on smoking status was observed for maternal age. This finding differs
to that frequently seen in other9,10,14 but not
all8,11 previous research.
Ethnic group differences were found in the present study
with Niuean, Other Pacific and Non-Pacific mothers being more likely to smoke
than their Samoan counterparts. Indicators of greater exposure to Westernisation
also predicted smoking status. Mothers residing in New Zealand for more than 10
years were more likely to be smokers than newer migrants. Similarly, a larger
proportion of mothers fluent in English smoked during pregnancy compared to
mothers not fluent. An Australian study containing a high proportion of
non-English speaking mothers, also observed differences between ethnic groups,
and found those mothers from English speaking backgrounds were more likely to
smoke than those from non-English backgrounds.8
In concordance with previous
research,2,9 higher parity increased likelihood
of smoking. Smoking may be used to relieve stress associated with the demands of
caring for more than one child, particularly for mothers with low psychosocial
resources.10 Alternatively, motivation to quit
smoking in the most recent pregnancy may have been reduced if no obvious
detrimental health outcomes were observed in previous pregnancies.
Non-attendance at antenatal classes was associated with a
two-fold increase in odds of smoking during pregnancy. Antenatal class
attendance in this cohort is low (8%) with a considerable proportion of first
time mothers not attending.25 Poor utilisation
of antenatal classes may indicate a lack of awareness surrounding health issues,
signifying the importance of reaching this group.
The behaviour of partners and other family members can
influence the smoking behaviour of pregnant
women,2 with those living with smoking
partners13,23or exposed to passive smoke by
others at home or at work10 being less likely
to stop smoking. For mothers in this study, living with at least one other
smoker more than quadrupled the likelihood of smoking during pregnancy. Thus,
despite a lack of success with some interventions aimed at enhancing partner
support to improve smoking cessation,26 it is
clear that the smokefree message needs to extend beyond childbearing women.
Interpretation of findings should be made recognising
possible limitations. The measurement of smoking status was based on use during
a specific timeframe, thus data regarding non-smokers may also include
ex-smokers. It is not known whether characteristics of ex-smokers in the present
study would differ markedly from non-smokers or whether this may have had any
influence on the relationships observed between smoking status, sociodemographic
factors, and other variables. The reliance on mothers’ reports may have
underestimated smoking behaviour so the possibility of reporting bias cannot be
ruled out. However, studies (that have compared the use of self-report versus
biomarkers of cigarette consumption) have shown self-reports to be an accurate
measure of smoking status,27,28 although,
measures of dose may be under-reported.28
Furthermore, reporting bias in the present study is likely
to be minimal given that smoking questions formed only a small part of the
overall interview content and that interviewers were not health workers. Despite
the possibility of some under-reporting of cigarette dose, our data provide an
estimate of patterns of consumption throughout pregnancy that can be further
explored in additional research.
In conclusion, for mothers of Pacific infants in New
Zealand, the present study showed that:
Factors identified as associated with
smoking during pregnancy can be used to better target mothers for smoking
cessation programmes. As smoking has many adverse health effects, which are
potentially dose-related and cumulative during pregnancy, stopping smoking as
early as possible is desirable and to be
encouraged.29 For those mothers who are not
motivated or unable to quit, education on ways to reduce possible harm to
infants should be a priority.30 Furthermore,
studies suggest that good smoking hygiene, such as not smoking in the same room
as the infant, require greater attention.31,32
The link between smoking and negative health consequences,
including respiratory illness,1 is widely
accepted. Smoking is a preventative risk factor for serious illness and places a
significant economic burden on society through additional healthcare
expenditure.4,33 Thus, greater emphasise should
be placed on disease prevention to reduce the health, social, and economic
burden caused by smoking.
Consideration of how to prevent women from taking up smoking
is of extreme importance and is likely to require a multifaceted
approach.19,26 As conventional programmes may
not appeal to or work for Pacific women, barriers to becoming smokefree warrant
further in-depth investigation, and cessation programmes designed specifically
for Pacific women are urgently needed.
Author information:
Sarnia Butler, Research Fellow, Pacific Islands Families: First Two Years of
Life Study, Auckland University of Technology, Auckland; Maynard Williams,
Senior Research Fellow and Statistician, Auckland University of Technology,
Auckland; Janis Paterson, Co-Director, Pacific Islands Families Study, Auckland
University of Technology, Auckland; Colin Tukuitonga, Pacific Health Research
Centre, Department of Maori & Pacific Island Health, University of Auckland
(and former Co-Director, Pacific Islands Families: First Two Years of Life
Study), Auckland
Acknowledgments: The
Pacific Islands Families (PIF) Study is supported by grants awarded from the
Foundation for Science, Research and Technology, the Health Research Council of
New Zealand, and the Maurice and Phyllis Paykel Trust. The authors gratefully
acknowledge the families who have participated in the study, the Pacific Peoples
Advisory Board, and other members of the PIF research team.
Correspondence:
Sarnia Butler, Faculty of Health Studies, Auckland University of Technology,
Private Bag 92006, Auckland. Fax: (09) 917 9877; email: sarnia.butler@aut.ac.nz
References:
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