Prevalence and Correlates of Secondhand Smoking Exposure Among Pregnant and Postnatal Chinese Women

Inhalation of secondhand smoke during pregnancy and postnatal period is detrimental to developing infants and increases risk for health problems throughout the lifespan. This study examined the prevalence of exposure to secondhand smoke, its correlates, and its association with QOL among pregnant and postnatal Chinese women. This multicenter, cross-sectional study was conducted in China. Participants were pregnant and postnatal women. We assessed associations of frequency and location of secondhand smoking with sample characteristics as well as depression and quality of life based on EPDS and WHOQOL-BREF, respectively.


Introduction
Both active smoking and exposure to secondhand smoking during pregnancy are well-known risk factors for compromised health and poor future health of infants. Studies have found that active smoking in pregnancy is associated with increased risk for low birth weight, small chest circumference, and sudden infant death syndrome, while exposure to secondhand smoking is associated with preterm delivery, fetal growth restriction, spontaneous abortion, and fetal death [1,2].
Secondhand smoking refers to involuntary inhalation of tobacco smoke by a nonsmoker for more than 15 minutes per week [3]. Women's exposure to secondhand smoking during pregnancy has varied from 17% to 94% [4][5][6][7]. Previous studies have found that exposure to secondhand smoking is more common than active smoking among pregnant women. For instance, a cross-sectional study in Greece showed that 36% of women reported active smoking, but 94% of these women were exposed to passive smoking during pregnancy [7]. A similar study in Taiwan found that 7.2% of pregnant women smoked during pregnancy, and 40.6% of these women were exposed to secondhand smoking [1]. A study in southern China found that 2.63% of pregnant women had a history of smoking; of these, 52.15% were also exposed to secondhand smoke during their pregnancy [8].
Pregnant and postnatal women are more likely to be exposed to secondhand smoking in public place and home settings. A study from Jordan found that considerable percentages of pregnant women were exposed to secondhand cigarette smoke (51.4%), and waterpipe smoke (48.7%) at home and in public spaces (31.4% and 21.4%, respectively). Within the home environment, husbands were the most common source of secondhand smoking [9]. A Chinese study found that public spaces were the most common setting of exposure to secondhand smoking (35.9% before pregnancy, and 37.2% during pregnancy, respectively), and more than 70% of women were exposed to secondhand smoking for 15-59 min/day [3].
Frequent correlates of secondhand smoking exposure during and/or after pregnancy included lower education level, and poorer mental health status [6,[8][9][10].
Secondhand smoking is common in China, with approximately 740 million secondhand smokers nationwide [3]. Smoking behaviour is determined by sociocultural factors and economic status [11], therefore, ndings derived from Western contexts may not be applicable to Chinese populations. Furthermore, although some relevant studies have been conducted in China, generalizations to the larger population cannot be made due to several limitations, such as small sample sizes and single-site study designs [12]. To the best of our knowledge, no studies to date have examined exposure to secondhand smoking among pregnant/postnatal women in China at multicenter settings [12]. In addition, quality of life (QOL) was de ned as individuals' perception of their lives in terms of culture and value systems in their living environment in relation to their goals, expectations and concerns [13]. No speci c studies on the association between exposure to secondhand smoking and QOL among pregnant/postnatal women were published in China. To address each of these gaps, we conducted this multicenter, cross-sectional study exploring the prevalence of exposure to secondhand smoking, its demographic correlates, and its association with QOL and depression among pregnant and postnatal women in China.

Methods
This study was conducted between February and October, 2019. Participants were consecutively recruited from eight territory hospitals located in eight municipality and provinces in China (i.e., Beijing, Xinjiang, Liaoning, Guangdong, Qinghai, Hubei, Jiangsu and Sichuan). Patients who were undertaking treatment in the participating hospitals during the study period were invited to take part in this study. Eligibility criteria included: 1) age 18 years or older, 2) currently pregnant or postnatal period (i.e., 1 week after child birth), and 3) ability to understand Chinese and provide written informed consent. Patients were excluded if they had severe physical diseases of any kind. Ethical approvals were obtained from respective hospitals. All participants were approached and invited by research nurses who explained the study aims and procedure. After obtaining written informed consent, face-to-face interviews were conducted.
A predesigned data collection sheet was used to collect basic demographic information (i.e., maternal age, education level, marital status, employment status, gestation, personal monthly income, history of miscarriage, placenta proposition, and physical comorbidities). Secondhand smoking was assessed by querying 1) frequency of exposure to secondhand smoking (≥15min/day) in the last 12 months via three options: '0' = < 1 day/week, '1' = 1-3 days/week, and '2' = 4-7 days/week. Those who endorsed option 1 or 2 were considered to be 'secondhand smokers'. Location of secondhand smoking (i.e., home, workplace, or public space) were also assessed [14].
The 10-item Edinburgh Postnatal Depression Scale (EPDS), Chinese version, was used to assess severity of self-reported depressive symptoms in the past week during pregnancy or the postnatal period [15].
Total EPDS scores range from 0 to 30, with higher scores indicating more severe depressive symptoms. The Chinese version of the EPDS has demonstrated excellent psychometric properties [16].
The World Health Organization Quality of Life Questionnaire (WHOQOL-BREF) was used to evaluate quality of life in physical, psychological, social and environmental domains [17]. Each item was scored from 1 to 5, with higher total scores indicating higher QOL. The Chinese version of the WHOQOL-BREF has satisfactory psychometric properties [18].

Data analysis
Kolmogorov-Smirnov tests were performed to examine normality in distributions of continuous variables.
Differences in basic demographics and clinical variables between pregnant/postnatal women exposed to secondhand smoking versus unexposed peers were assessed using independent samples t-tests, Chisquare tests or Mann-Whitney U tests, as appropriate. Multiple logistic regression analysis was performed to examine the independent demographic and clinical correlates of exposure to secondhand smoking. Secondhand smoking was the dependent variable, while measures on which there were signi cant group differences in univariate analyses were entered as independent variables. Group differences in QOL between women exposed to secondhand smoking and unexposed women were examined using analyses of covariance (ANCOVA) controlling for other variables on which these groups differed in univariate analyses. Data analyses were performed using SPSS V24.0. The signi cance level was set at 0.05 (twotailed) for each analysis.

Results
A total of 1,140 women were invited to join this study and 992 (87.02%) completed all measures. From the entire sample, 211 women (21.3%, 95%CI=18.7-23.8%) suffered from secondhand smoking. Secondhand smoking exposure was more common in public areas (56.4%) than home environment (20.5%). Demographic and clinical characteristics of participants are presented in Table 1.
In univariate analyses, women who were younger (P<0.001) or in their third trimester (P=0.015), and those with physical comorbidities (P=0.023) were more likely to report secondhand smoking exposure. Those living in urban areas (P<0.001), having higher education levels (P<0.001), and earning higher monthly incomes (P=0.011) were less likely to report secondhand smoking exposure. Finally, there were no signi cant differences in depressive symptoms or QOL domains between women who were exposed to secondhand smoking exposure and non-exposed peers.
Multiple logistic regression analysis revealed that women who reported physical comorbidities were more likely to report secondhand smoking exposure (

Discussion
This is the rst multicenter, large-scale study to examine the prevalence of secondhand smoking and its association with QOL among pregnant and postnatal women in China. Over one-fth (21.3%) of pregnant and postnatal women experienced secondhand smoking in the sample, a rate that is noticeably lower than gures reported by previous research based on single study sites [8,10,19]. For example, Wen et al. (2016) reported that 52.1% of pregnant Chinese women had been exposed to secondhand cigarette smoking during their pregnancy while Yang et al. [10] found that 75.1% of non-smoking pregnant women reported regular exposure to secondhand smoking through their smoking husband. Caution is warranted in interpreting generalizability of ndings from previous studies based on participants recruited from only one Chinese province [12]. In more recent years, there seems to be a heightened awareness of harmful effects of smoking on perinatal health and health of unborn infants [20], so pregnancy is considered to be a golden opportunity for smoking cessation [21]. In addition, comprehensive tobacco control policies and anti-nicotine educational campaigns have been well-developed and implemented in China over the past few years. Anti-smoking policy development and heightened public awareness may explain the relatively lower prevalence of secondhand smoking in this study compared to past work.
Physical comorbidities were positively associated with secondhand smoking, a nding that echoes previous research linking secondhand smoking during pregnancy to various negative health outcomes, such as preterm delivery, fetal growth restriction, spontaneous abortion, birth defects, and fetal death [1,2]. Secondhand smoking can also increase risk for atherosclerosis and cardiovascular diseases, lung cancers, oral and esophageal cancers, and bone marrow myeloid leukemia [9]. Potential mechanisms for physical comorbidities include decreased oxygen supply and the enhanced production of free radicals [22] that impair cellular constituents, in uence protein oxidation, and even cause damage to the DNA. Dovetailing with results of previous studies [7,8,10], we found that less educated women were more likely to be exposed to secondhand smoking than women with higher education levels. People with higher education levels often have more awareness of potential harm induced by passive smoking behaviors [7]. Based on this assumption, anti-nicotine educational programs targeting at women of reproductive age and their spouses to decease tobacco consumption behaviour and provide a smoke-free environment may be especially useful for reducing exposure to secondhand smoking among pregnant/postnatal women and their infants.
Associations between residence and women's active and passive (secondhand smoking) behaviors have been inconsistent. Some studies have found that pregnant women in rural areas are more likely to be exposed to secondhand smoking [3,7], which other research has found no such relationship [19]. In this large-scale study, women in urban areas were less likely to report secondhand smoking during pregnancy than did rural cohorts. One plausible hypothesis that may contribute to this difference is that women and their spouses living in rural area may receive less public health advice and guidance about negative health outcomes of smoking behaviour during pregnancy. In addition, tobacco control policies and measures are more often poorly enforced in rural areas. Taken together, these contentions suggest geographical region and anti-smoking policy enforcement may play a pivotal role in active and secondhand smoking behavior among pregnant and postnatal women. Previous research has not found signi cant associations between pregnancy phase and secondhand smoking [3,9,19]. However, in this study, women in their second trimester were less likely to experience secondhand smoking. In light of its novelty, this nding warrants additional attention in future work to evaluate its replicability.
Finally, there were no statistically signi cant differences between women exposed to secondhand smoking and non-exposed peers in relation to self-reported depressive symptoms or QOL domains. Our ndings con ict with results from two systematic reviews that have linked exposure to secondhand smoking during pregnancy to increased risk for depressive symptoms, which could impede QOL [23,24]. This discrepancy could be due to variations in sample size, use of different assessment tools, and socioeconomic status differences between studies. Arguably, the WHOQOL-BREF is a generic measure that may not be sensitive enough to detect minor changes of QOL in pregnant and postnatal women. Conversely, given that theoretical bases for links between exposure to secondhand smoking and QOL are not well developed, other correlates of exposure such as socioeconomic status may be more critical in uences on this relationship.
Strengths of this study included its multicenter design, large sample size, and use of standardized measurements on depressive symptoms and QOL. However, several limitations should be noted. First, casual relationships between sociodemographic, clinical variables and secondhand smoking cannot be established due to the cross-sectional design. Second, the impact of recall biases on ndings cannot be ruled out given that data were collected using self-reported instruments. Third, unmeasured correlates of secondhand smoking behaviors, such as, interpersonal relationships, violence experience, and family support were not investigated in this study but have potential relevance to exposure [25,26].

Conclusion
In conclusion, the prevalence of exposure to secondhand smoking was lower among pregnant and postnatal Chinese women in this study compared to ndings reported in previous studies based on smaller, less general samples. Considering the detrimental impact of secondhand smoking on health of pregnant and/or postnatal women and their infants, it is important to establish smoke-free environments in both public and private places for this group, particularly for those who are less-educated, living in rural areas, and have physical comorbidities. Anti-smoking education and tobacco control policies should extend beyond urban areas to rural areas of China. Psychosocial interventions to facilitate smoking cessation should also be considered given that bene cial health outcomes may result for mothers, infants, and their families.

Declarations
Acknowledgements None. Sources of Funding The study was supported by the University of Macau Hospital. All participants provided informed consent form. Availability of data and material The data of the investigation will be made publicly available if necessary. Consent for publication Not applicable. Contribution to the eld Smoking behaviour is determined by sociocultural factors and economic status, ndings derived from Western contexts may not be applicable to Chinese populations. This study found that the prevalence of exposure to secondhand smoking is becoming lower among pregnant and postnatal women in China. About 21.3% women had been exposed to secondhand smoking. Secondhand smoking was most common in public areas (56.4%). Women with physical comorbidities were more likely to report exposure, while younger women, women living in urban areas, and those with higher education level were less likely to report.