Article Text
PDF
Abstract
Objectives Postpartum depression (PPD) is a prevalent complication of childbearing, with numerous risk factors associated with its onset. Although the risk factors for PPD among postpartum women have been studied, the mechanisms underlying these factors remain inadequately understood. This study aimed to investigate the direct and mediating roles of different coping styles in the relationship between dyadic adjustment status and PPD among women 6 weeks postdelivery.
Design Single-centre, cross-sectional study.
Setting A tertiary care setting in Chengdu City, Sichuan Province, China, from July 2022 to January 2023.
Participants The study involved 626 women 6 weeks post-delivery.
Outcome measures The Dyadic Adjustment Scale, the Simplified Coping Style Questionnaire and the Edinburgh Postnatal Depression Scale (EPDS) were used to evaluate the dyadic adjustment status, coping styles and the depressive condition of postpartum women, respectively. Data analysis encompassed correlation and mediation analyses based on structural equation modelling.
Results EPDS scores were significantly correlated with all four dimensions of dyadic adjustments status as well as with both positive and negative coping styles. Dyadic consensus (β = −0.16, p=0.005), affectional expression (β = −0.14, p=0.008) and dyadic cohesion (β = −0.10, p=0.037) directly correlated with PPD after adjusting for covariates. For dyadic satisfaction, the mediating effects of positive and negative coping styles on PPD were −0.04 (95% CI: −0.08 to –0.01) and −0.07 (95% CI: −0.11 to –0.03), respectively. Moreover, both positive and negative coping styles were identified as mediators in the relationship between dyadic cohesion and PPD, with mediating effects of −0.01 (95% CI: −0.03 to –0.00) and −0.09 (95% CI: −0.14 to –0.04), respectively. No mediation was found in the association between affectional expression and PPD.
Conclusion Our findings suggest that both positive and negative coping styles mediate the relationship between dyadic adjustment status and PPD, especially concerning dyadic satisfaction and dyadic cohesion.
- Depression & mood disorders
- Postpartum Women
- MENTAL HEALTH
Data availability statement
The data were collected and collated by the research team. Due to specific privacy and confidentiality restrictions, they are unavailable for public access.
This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.
Statistics from Altmetric.com
STRENGTHS AND LIMITATIONS OF THIS STUDY
Data collection was conducted by trained and qualified obstetric nursing professionals, who were proficient in recognising the emotions of the delivering women and adept at communicating with the participants, under the supervision of the principal investigator.
The Edinburgh Postnatal Depression Scale, the Simplified Coping Style Questionnaire and the Dyadic Adjustment Scale were used for data collection to evaluate postpartum depression, different coping styles and marital status.
The reliance on convenience sampling data might introduce potential sampling bias.
This study reflected the relationships among variables within a specific time period only, and the cross-sectional design precludes the establishment of causal relationships.
Introduction
Postpartum depression (PPD), a combination of depressed mood, sleep and appetite disturbances, impaired concentration and fatigue, is a common psychiatric disorder that occurs following childbirth. It is particularly prevalent among new mothers and often persists for an extended duration.1 According to epidemiological data, the prevalence of PPD is estimated by using standardised validated instruments to be 17.22% of the global population.2 Recently, the prevalence rate of PPD among Chinese women from the seventh day to the sixth month after childbirth has fluctuated between 29.1% and 38.0%.3 4 Those estimations are higher than the prevalence rate of 8.3% at 8 weeks postpartum, as reported in a cohort study involving 3310 Caucasian women.5 The repercussions of PPD on new mothers could lead to a range of detrimental outcomes, including impaired psychological health, cognitive issues and malnutrition in their offspring. In addition, maternal conditions such as insomnia and anorexia may hinder the ability to provide adequate childcare, generating a stressful environment that adversely affects marital relationships as well.6 7
Various risk factors of PPD have been identified, mainly including personal physical and psychological status, neonatal status, cultural beliefs, socioeconomic status, reporting disparities, differing perspectives on mental health disorders and regional economic factors.8 9 Dyadic adjustment is a specific construct established within social science to explore the role of certain variables in marital adjustment.10 A stable and satisfying marital relationship is considered a protective factor against PPD, while supportive partners significantly contribute to reducing stress and enhancing the psychological well-being of new mothers.11 Although the importance of marital adaption status in postpartum women is recognised, the mechanism through which it impacts these outcomes remains largely unclear.
In addition to dyadic adjustment status, passive coping is another significant predictor of depression that surpasses racial and population differences.12 A longitudinal study conducted in China demonstrated that pregnant women with higher levels of positive coping in the third trimester were less prone to PPD.13 Coping style refers to the cognitive and behavioural changes employed to manage stressful circumstances perceived as demanding, challenging, threatening or potentially harmful.14 Coping styles could be categorised by their nature (positive or negative) and focus (problem or emotion focused).15 16 Engaging in positive coping mechanisms has been shown to help mitigate adverse effects, whereas reliance on passive emotional coping strategies may negatively impact psychological and physical health.17 Positive coping styles can be fostered by healthy marital relationships, as such good relationships promote supportive communication and a preference for constructive stress management.18 A study19 on marital satisfaction among Chinese married individuals demonstrated that positive coping styles had a positive prediction on marital satisfaction, whereas negative coping styles had a negative prediction on it. Specifically, postpartum women with poor marital relationships were prone to adopt dysfunctional coping strategies, such as venting emotions and avoiding problems, which could precipitate PPD. In contrast, women employing positive coping mechanisms were less likely to experience PPD. Besides, a robust matrimonial bond has been found to enhance women’s mental health and improve maternal postnatal attachment.20
Therefore, it is plausible to suggest that dyadic adjustment status, PPD and coping styles are interconnected and interact with one another, with coping styles potentially mediating the relationship between dyadic adjustment status and PPD. In the current study, we aimed to explore the direct and mediating roles of different coping styles in the relationship between dyadic adjustment and PPD in this context. We propose the following three hypotheses: (a) PPD is related to coping styles and dyadic adjustment status, (b) dyadic adjustment status is connected with coping styles and (c) coping styles serve as a mediator in the relationship between dyadic adjustment status and PPD (figure 1). Our findings regarding the potential impacts of coping styles are anticipated to assist in the development of targeted interventions, thereby enhancing the mental health of postpartum women, which in turn benefits their infants.
Hypothesised mediation effect model. AE affectional expression, DCN dyadic cohesion, DCS dyadic consensus, DS dyadic satisfaction, EPDS Edinburgh Postnatal Depression Scale, NEC negative coping styles, POC positive coping styles, PPD postpartum depression.
Methods
Study design and participants
This was a cross-sectional study conducted at Second West China Hospital of Sichuan University. We chose to conduct the survey in the sixth week after giving birth, according to the finding that the peak time for PPD to manifest is approximately 42 days postpartum.21 Postpartum women aged 20 or older were prospectively recruited between July 2022 and January 2023. Convenience sampling was adopted to enrol delivery women who were attending outpatient re-examinations at this hospital. While they were waiting for examination, all eligible women were invited to participate in the study. Participants were required to possess the ability to complete the research independently and have a stable partner. Individuals with severe comorbidities (eg, malignancy and severe pancreatitis) and those with a personal or immediate family history of psychiatric disorders were excluded from the study. The initial assessment and recruitment were performed by obstetric nurses who had undergone uniform training including comprehension of the data collection tools, assessment of the postpartum women, communication and interpersonal skills training. The estimated sample size was calculated using G*Power software, V.3.1.9.7. An effect size of 0.15 was employed, with a significance level of α = 0.05 and a statistical power of 1 − β = 0.90. Accounting for an anticipated inefficiency rate of 10% within the data, the ultimate sample size was consequently determined to be 183.
This study was conducted in accordance with the ethical guidelines of the Declaration of Helsinki, and the protocol (no. 2019 (002)) was reviewed and approved by the ethics committee of West China Second University Hospital of Sichuan University. All participants were provided with a detailed and thorough explanation of the research, and prior to their involvement, they each signed an informed consent form. Basic characteristics of each participant were collected, including age, educational level, monthly family income, residence and relationship with caregiver. In addition, obstetric information (eg, gravity, mode of delivery and complications) and infant-related factors (eg, neonate sex satisfaction, neonate condition and difficulties in breastfeeding) were also considered. A copy of the questionnaire is included in the online supplemental file.
Supplemental material
Measurements
Dyadic adjustment status
The Dyadic Adjustment Scale (DAS), developed by Spanier and later revised by Shek,22 was employed to assess the quality and adjustment status of marriage.23 This scale comprises 32 items that assess four dimensions: affectional expression, dyadic consensus, dyadic cohesion and dyadic satisfaction. Each item is rated on a scale ranging from ‘always consistent’ to ‘always inconsistent’. The total score ranges from 0 to 151, where higher total and subscale scores indicate a more positive appraisal of the marriage. The subscale can be used individually without compromising its reliability or validity. The psychometric properties of this scale have been confirmed in Chinese populations,24 demonstrating good internal consistency with a Cronbach’s alpha coefficient of 0.85 and a retest reliability of 0.88. The DAS exhibited excellent internal consistency, with a Cronbach’s alpha coefficient of 0.93 in our study.
Coping styles
The Simplified Coping Style Questionnaire (SCSQ), revised on the basis of the coping Questionnaire designed by Folkman et al,25 was used to assess coping style. The questionnaire consists of 20 items categorised into two dimensions, namely positive coping style and negative coping style. Positive coping styles include the use of active thinking, viewing problems from a positive perspective and effectively dealing with issues. Conversely, negative coping styles involve intense negative emotions such as irritability, depression or grief, avoidance of reality, rumination and an inability to independently resolve problems.26 Each item is rated on a 4-point scale ranging from ‘never=0’ to ‘always=3’, with higher scores indicating a more frequent use of the respective coping style. The SCSQ demonstrated good internal consistency with a Cronbach’s alpha coefficient of 0.90, and the retest reliability was 0.89. The Chinese version of the SCSQ demonstrated satisfactory reliability among pregnant women.27 In this study, the SCSQ showed good internal consistency, with a Cronbach’s alpha coefficient of 0.82.
Postpartum depression
The Edinburgh Postnatal Depression Scale (EPDS), developed by Cox, is widely regarded as the common standard for measuring PPD in women.28 The psychometric evaluation of the Chinese version of this scale was validated by Wang et al 29 and consists of 10 items. Each item is rated on a 4-point scale ranging from 0 to 3, yielding a total score between 0 and 30. A higher score indicates a higher probability of depression.30 The Cronbach’s alpha for the EPDS was 0.79, and the retest reliability was 0.85. This scale has been extensively used among prenatal and postnatal women in China.31 32 A cutoff score of 10 has been established as valid for the Chinese version of this scale.33 Therefore, a score of 10 has been established as a valid threshold for determining the prevalence of PPD in this study. The EPDS demonstrated good internal consistency, with a Cronbach’s alpha coefficient of 0.83 in our data.
Statistical analysis
Descriptive statistics were used to summarise the basic characteristics of the participants, as well as the scores from the DAS, SCSQ and EPDS. Pearson correlation analysis and multivariate analysis were employed to explore the correlations among dyadic adjustment, coping styles and depression. Structural equation modelling (SEM) was applied to examine the path relationships among measured variables. The goodness of fit for the SEM was evaluated using several indices: chi-square/degrees of freedom (χ²/df<3.00), root mean square error of approximation (RMSEA≤0.08), goodness-of-fit index (GFI>0.90), comparative fit index (CFI≥0.95) and Tucker-Lewis Index (TLI>0.90). Subsequently, SEM was used to investigate whether positive and negative coping styles mediated the association between the dimensions of dyadic adjustment status and PPD, using bias-corrected percentile bootstrap (5000 times). All statistical analyses were performed using SPSS 25.0 and Amos 21.0.
Patient and public involvement
Patients and/or the public were not involved in this study.
Results
Characteristics of participants and scores for dyadic adjustment status, coping styles and PPD
Among the 660 participants initially recruited, 626 individuals were included in the final analysis after applying the exclusion criteria (online supplemental figure S1). The response rate was 94.8%. The mean EPDS score for all women was 8.21 (± 5.58), resulting in a prevalence of PPD of 22.6% based on a cutoff score of 10. The majority of the participants resided in urban areas (91.5%) and had a university-level education (91.2%). Additionally, a significant proportion (86.3%) reported a family income exceeding 5000 CNY per month. Women who experienced delivery complications had higher depression scores (p=0.004). Those with poor caregiver relationships exhibited higher scores on EPDS (p<0.001) and negative coping style (p=0.006), along with lower scores on all dimensions of DAS and positive coping style (p=0.006) (table 1). Moreover, women whose infants faced breastfeeding difficulties demonstrated higher scores in EPDS (p=0.002) and negative coping style (p=0.035). When participants were divided into two groups based on other baseline indicators, no significant differences were observed in DAS, SCSQ or EPDS between the two groups.
Supplemental material
DAS, EDPS and SCSQ scores among participants with different characteristics (n=626)
Correlations among EPDS scores/PPD risk, dyadic adjustments and coping styles
The EPDS scores of women were found to have a negative correlation with dyadic consensus (r: −0.42, 95% CI: −0.35 to –0.50, p<0.001), dyadic satisfaction (r: −0.40, 95% CI: −0.32 to –0.49, p<0.001), affectional expression (r: −0.41, 95% CI: −0.33 to –0.48, p<0.001), dyadic cohesion (r: −0.42, 95% CI: −0.34 to –0.49, p<0.001) and positive coping style (r: −0.33, 95% CI: −0.25 to –0.42, p<0.001) (figure 2). Conversely, EPDS scores were positively correlated with negative coping style (r: 0.48, 95% CI: 0.41 to 0.55, p<0.001). As expected, positive coping style demonstrated a positive correlation with dyadic consensus (r: 0.34, 95% CI: 0.25 to 0.42, p<0.001), dyadic satisfaction (r: 0.52, 95% CI: 0.43 to 0.59, p<0.001), affectional expression (r: 028, 95% CI: 0.20, 0.36 to p<0.001) and dyadic cohesion (r: 0.37, 95% CI: 0.29 to 0.45, p<0.001). Moreover, negative coping style showed a negative correlation with dyadic consensus (r: −0.16, 95% CI: −0.07 to –0.25, p<0.001), dyadic satisfaction (r: −0.30, 95% CI: −0.22 to –0.38, p<0.001), affectional expression (r: −0.16, 95% CI: −0.07 to –0.24, p<0.001) and dyadic cohesion (r: −0.33, 95% CI: −0.25 to –0.41, p<0.001). These findings underscore the interrelation among dyadic adjustment status, coping styles and EPDS scores. Multivariate logistics regression model indicated that dyadic consensus (OR: 0.95, 95% CI: 0.92 to 0.99, p=0.019), affectional expression (OR: 0.83, 95% CI: 0.71 to 0.97, p=0.022), positive coping style (OR: 0.94, 95% CI: 0.91 to 0.98, p=0.002) and negative coping style (OR: 1.18, 95% CI: 1.13 to 1.23, p<0.001) were significantly associated with PPD after adjusting for age, relationship with caregivers, breastfeeding difficulty and complications. Although dyadic satisfaction (OR: 0.92, 95% CI: 0.90 to 0.94, p<0.001) and dyadic cohesion (OR: 0.88, 95% CI: 0.86 to 0.91, p<0.001) were shown to correlate with PPD in univariate analysis, these correlations did not persist in the multivariate model (p>0.05). This discrepancy suggests that their correlation with PPD may be confounded by other factors (table 2).
Pearson correlations analysis among dyadic adjustments, coping styles and PPD risk.
Univariate and multivariate analyses of risk factors of PPD (n=626)
Mediating effect of coping styles in the relationship between dyadic adjustment status and PPD
The mediation model showed a good fit (χ2/df=2.124, RMSEA=0.042, GFI=0.998, CFI=0.997, TLI=0.985). As expected, three dimensions of dyadic adjustment, specifically dyadic consensus (β = −0.16, p=0.005), affectional expression (β = −0.14, p=0.008) and dyadic cohesion (β = −0.10, p=0.037) were negatively related to PPD. Surprisingly, dyadic satisfaction did not exhibit a statistically significant effect on PPD, with a β of 0.06 (p=0.356). All path coefficients have been normalised (figure 3).
Structural model with standardised estimates. Fit indices of model‚ χ²/df=2.124, RMSEA=0.042, GFI=0.998, AGFI=0.973, CFI=0.997, TLI=0.985. AE, affectional expression; DCN, dyadic cohesion; DCS, dyadic consensus; DS, dyadic satisfaction; EPDS, Edinburgh Postnatal Depression Scale; NEC, negative coping styles; POC, positive coping styles; PPD, postpartum depression. ∗p<0.05, ∗∗p<0.01, ∗∗∗p<0.001.
Consequently, we conducted additional mediation analysis by controlling for covariates. Results indicated that dyadic consensus was positively related to positive coping style (β=0.13, p=0.011). Dyadic satisfaction exhibited a positive association with positive coping style (β=0.43, p<0.001) and was negatively associated with negative coping style (β = −0.19, p<0.001). Similarly, dyadic cohesion demonstrated a positive correlation with positive coping style (β=0.10, p=0.018) and a negative correlation with negative coping style (β = −0.24, p<0.001). Both positive and negative coping styles were significantly related to PPD (β = −0.10, p=0.009; β=0.36, p<0.001, respectively). Furthermore, we assessed the mediating effects of coping styles in the relationships between specific dyadic adjustment dimensions and PPD. The mediating effect of positive coping style on the association between dyadic consensus and PPD was −0.01 (95% CI: −0.04 to –0.00). For dyadic satisfaction, the mediating effects of positive and negative coping style on PPD were −0.04 (95% CI: –0.08 to –0.01) and –0.07 (95% CI: –0.11 to –0.03), respectively. Likewise, the mediating effect of positive and negative coping style on the association between dyadic cohesion and PPD were –0.01 (95% CI: –0.03 to –0.00) and –0.09 (95% CI: –0.14 to –0.04), respectively, indicating a considerable mediating role. However, no mediating effect was detected in the relationship between affectional expression and PPD when assessed through either positive or negative coping style as a mediator. Accordingly, our findings support (a) the significant correlations of coping styles and dyadic adjustment status with PPD, (b) the association of dyadic consensus, dyadic satisfaction and dyadic cohesion with positive coping style, alongside the linkage of dyadic satisfaction and dyadic cohesion with negative coping style and (c) the partial mediation of coping styles in the relationship between dyadic adjustment status and PPD.
Discussion
The study explored the associations among dyadic adjustment status, coping styles and PPD in a cohort of 626 participants. The prevalence of PPD in our study was as high as 22.6%, which is consistent with previous reports from China34 35 and other countries.36 37 This indicates that PPD is a widespread issue across diverse geographical regions, including West China, and underscores the need for heightened awareness and proactive intervention measures. Numerous factors associated with PPD have been identified, including gestational and postpartum complications, premenstrual syndrome, a history of depression, socioeconomic factors (such as low income or single parenthood) and intrafamily conflicts.36 38 39 Notably, poor relationships with caregivers and dyadic conflicts have been extensively discussed.40 41 Unstable partner relationships, family conflicts and inadequate emotional support can hinder postpartum women from overcoming challenges and accessing available coping resources,42 thereby leading to an increased prevalence of PPD. Additionally, difficulty in breastfeeding has emerged as a significant factor associated with PPD.35 These findings highlight the importance of focusing on marital quality and family support when addressing the mental health needs of women. It is also noteworthy that recent studies have identified emerging risk factors, such as exposure to pervasive environmental chemicals (eg, phthalates)43 and a history of hormonal contraception-associated depression.44
The current study found a negative relationship between all four dimensions of dyadic adjustment status and PPD, which aligns with previous report8 suggesting a decreased risk of PPD in postnatal women with improved marital adjustment. Notably, the dimensions of dyadic consensus and affectional expression were significantly correlated with the risk of PPD. In essence, positive marital quality enhances women’s resilience in navigating the challenges of the postpartum period.45 Moreover, a meta-analysis42 identified marital status as a predictor of PPD, linking poor dyadic adjustment to deteriorated maternal mental well-being.46 The transition to parenthood often introduces new responsibilities, increased demands, reduced time for couples and heightened marital conflict, all of which contribute to diminished relationship satisfaction and, consequently, an increased risk of PPD.45 However, dyadic satisfaction did not exhibit a significant negative association with PPD in the current study. This outcome may be attributed to the prevalence of modern notions of free love, which foster a generally higher level of marital satisfaction among the majority of participants. The limited number of individuals expressing marital dissatisfaction in our study may have precluded a robust analysis of its potential as a risk factor for depression. This limitation underscores the need for future research specifically designed to explore this aspect in greater depth.
Dyadic adjustment status has previously been identified as a mediator in the relationship between depression, anxiety and partners’ antenatal attachment to the fetus during pregnancy.47 In contrast, our study extends this understanding by demonstrating that dyadic adjustment affects depression through coping styles. We specifically elucidated the mediating roles of both positive and negative coping styles in the relationships between dyadic satisfaction, dyadic cohesion and PPD. A previous study18 indicated that enhanced marital relationships foster more supportive communication and a preference for constructive stress management, culminating in a positive coping style. Women who were content with their partners often experienced better marital relationships, enabling them to proactively confront challenges.48 Moreover, our findings also demonstrated that participants with husbands who regularly expressed affection and engaged in playful activities were more inclined to adopt optimistic and positive problem-solving approaches. In contrast, individuals with less intimacy and fewer shared activities with their partners were more prone to engage in negative coping mechanisms or to avoid addressing issues with their partners. Additionally, a positive coping style serves as a mediator between dyadic consensus and PPD. Women who shared accordant consensus with their husbands on critical matters such as religion, belief and household management tended to adopt a positive outlook.49 As a result, they were more likely to address issues positively when they had a stronger bond with their husbands. Embracing a positive coping strategy allows individuals to perceive and tackle problems from a more optimistic perspective, thereby reducing their susceptibility to depression. Conversely, those who resort to negative coping strategies—such as avoidance and rumination—are more vulnerable to depression.50 Cognitive reappraisal, as suggested by previous research, plays a crucial role in regulating positive emotions and is positively associated with subjective well-being.51 In contrast, coping strategies such as rumination, self-blame, avoidance and rejection have been linked to increased distress, anxiety and depression.52 However, in our study, neither positive nor negative coping styles demonstrated a mediating effect in the relationship between affectional expression and PPD, despite the negative impact of affectional expression on PPD. This discrepancy may be attributed to the essential role of expression in communication. Inadequate expression within a marital relationship can lead to communication issues, thereby exacerbating PPD. Women experiencing more dysfunctional communication within their families are consequently more prone to PPD.53
While the relationship between overall marital adjustment and depression has been explored, our study delves into the connections among depression, coping styles and the specific dimensions of dyadic adjustment status. These nuanced analyses have the potential to lay a theoretical foundation for future research and development of intervention strategies.
We conducted a study to evaluate women’s depressive status at the sixth week after delivery and uncovered the roles of coping styles in the relationship between dyadic adjustment status and PPD. However, a notable limitation of our study is its reflection of the relationships among variables within a specific time period and does not establish causal relationships due to its cross-sectional design. Furthermore, while the participant pool included individuals from various provinces and cities in the southwest region, the single-centre nature of the study constrains the generalisability of our findings. Additionally, convenience sampling was employed, which may introduce sampling bias and potentially influence the representativeness of the sample. Future research could address these limitations by conducting multicentre studies that incorporate a wide range of cultural and socioeconomic backgrounds. Longitudinal studies are recommended to elucidate the causal relationships among dyadic adjustment status, coping styles and PPD.
Conclusion
Coping styles mediate the relationships between dyadic adjustment status and postpartum depression in distinct ways, particularly regarding dyadic satisfaction, and dyadic cohesion. Women with better marital adjustment tend to adopt positive coping strategies, thus reducing the likelihood of depression. Consequently, it is essential to improve marital quality, strengthen family support and assist women in developing positive coping strategies. By recognising and addressing these contextual factors, interventions and support services can be tailored more effectively to meet the unique challenges encountered by postpartum women. This will be beneficial in alleviating the prevalence of PPD and thus enhancing women’s psychological health.
Data availability statement
The data were collected and collated by the research team. Due to specific privacy and confidentiality restrictions, they are unavailable for public access.
Ethics statements
Patient consent for publication
Ethics approval
This study was conducted in accordance with the ethical guidelines of Declaration of Helsinki, and the protocol (no. 2019 (002)) was reviewed and approved by the ethics committee of West China Second University Hospital of Sichuan University. All participants were provided with a detailed and thorough explanation of the research, and prior to their involvement, they each signed an informed consent form.
Acknowledgments
We are grateful to the participants for their contributions to this study.
References
Footnotes
Contributors XG made important intellectual contributions in conception and design of this study. JC, XG and FL were responsible for the acquisition and interpretation of data. JD was responsible for manuscript writing and data analysis with YT. YT, XG and FL contributed considerably to the revision of the manuscript. All authors read and approved the final version of the manuscript. JD is the guarantor.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient and public involvement Patients and/or the public were not involved in the design, conduct, reporting or dissemination plans of this research.
Provenance and peer review Not commissioned; externally peer reviewed.
Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.