The Multiple Mediating Effects of Internalized Weight Stigma, Breastfeeding Difficulties, and Breastfeeding Self-Efficacy on the Association Between Pre-pregnancy Overweight/Obesity and Exclusive Breastfeeding at 6 Months Postpartum: A Prospective Cohort Study

doi:10.21203/rs.3.rs-5031866/v1

Background

Despite the World Health Organization's (WHO) emphasis on the essential role of exclusive breastfeeding for both maternal and infant health, exclusive breastfeeding rates among women with pre-pregnancy overweight/obesity remain suboptimal. The underlying mechanisms driving this negative association are not well-understood. This study aimed to explore these mechanisms by examining the independent and sequential mediation effects of internalized weight stigma, breastfeeding difficulties, and breastfeeding self-efficacy on the relationship between pre-pregnancy overweight/obesity and exclusive breastfeeding at six months postpartum.

Methods

In this prospective cohort study, 296 primiparous women were stratified by pre-pregnancy body mass index (BMI) into two groups: pre-pregnancy overweight/obese (n = 146) and normal BMI (n = 150). Data were collected via questionnaires during the antenatal period and at 6 months postpartum. After adjusting for covariates, structural equation modeling with maximum likelihood estimation was utilized, along with bias-corrected bootstrap testing, to estimate and assess the mediation effects in the negative association between maternal pre-pregnancy overweight/obesity and exclusive breastfeeding at 6 months postpartum.

Results

The study confirmed a negative correlation between pre-pregnancy overweight/obesity and exclusive breastfeeding at 6 months postpartum. Significant indirect paths were identified from pre-pregnancy overweight/obesity to exclusive breastfeeding at 6 months postpartum through internalized weight stigma (β = −0.217, p = 0.001), breastfeeding difficulties (β = −0.078, p = 0.018), and breastfeeding self-efficacy (β = −0.052, p = 0.025), each contributing separately. Additionally, a significant indirect path was found through the serial mediation of breastfeeding difficulties and breastfeeding self-efficacy (β = −0.053, p = 0.001).

Conclusions

This study elucidated the complex relationship between pre-pregnancy overweight/obesity and reduced exclusive breastfeeding rates at 6 months postpartum, identifying internalized weight stigma, breastfeeding difficulties, and decreased breastfeeding self-efficacy as significant mediating factors. Future research should concentrate on developing targeted interventions to overcome these obstacles, potentially including psychological therapies, hands-on breastfeeding support, and self-efficacy enhancement.

Trial registration

This study was registered at the Chinese Clinical Trial Registry (http://www.chictr.org.cn/, registry number: ChiCTR2200057038). The trial registration date was (26/02/2022).

Pre-pregnancy body mass index

Internalized weight stigma

Breastfeeding difficulties

Breastfeeding self-efficacy

Exculsive breastfeeding

Breastfeeding is recognized as the gold standard in infant nutrition, facilitating the acceptance and preference for healthy foods after weaning, which is crucial for preventing childhood obesity [1, 2]. Research has indicated that breastfeeding for 1 month can lower the risk of childhood obesity by 36% while extending breastfeeding to beyond 6 months further reduces the risk by 42% [3]. The World Health Organization emphatically recommends exclusive breastfeeding during the first 6 months of life [4]. Despite these guidelines, the prevalence of exclusive breastfeeding in China remains alarmingly low at 29.2% [5]. However, those who stand to benefit most from extended breastfeeding periods often face substantial barriers to adhering to exclusive or recommended breastfeeding durations. Accumulating evidence has revealed that women with pre-pregnancy overweight/obesity are less likely to sustain exclusive breastfeeding or to follow recommendations for the delayed introduction of solid foods sooner than normal-weight women [6, 7]. Amid the escalating rates of overweight and obesity among women of childbearing age worldwide, the success of breastfeeding in this population is crucial for meeting community nutrition objectives [8, 9]. Nonetheless, the mechanisms underlying the negative association between pre-pregnancy overweight/obesity and exclusive breastfeeding remain inadequately explored.

However, weight-related issues, along with factors such as poor latch, difficulties in infant positioning, and inadequate milk ejection, may significantly impact breastfeeding [10, 11]. Social misconceptions about individuals with overweight/obesity, known as weight stigma, can lead to both external weight-based discrimination and internalized weight stigma (IWS) [12]. IWS manifests as self-devaluation resulting from negative weight-based attitudes and stereotypes and encompasses a fear of stigma [12]. Specifically, IWS is characterized by the acceptance and incorporation of society’s negative stereotypes about weight into one’s sense of self and personal value system [13]. In the obstetric setting, subtle forms of weight discrimination, such as accusatory communication from healthcare professionals, coexist with overt discrimination, including verbal remarks and refusal to treat women with overweight/obesity seeking pregnancy care [14]. Additionally, the perinatal period is a time when women experience dramatic changes in body shape and weight (e.g., increased breast size, thickening of the waist, and widening of the hips) that diverge from societal standards favoring a slender and thin body type, thereby exacerbating weight stigma [15, 16]. The weight-based stereotypes and discrimination faced by perinatal individuals with overweight/obesity lay the groundwork for the perpetuation of IWS [17]. IWS adversely influences health behaviors, potentially lowering the probability of meeting personal breastfeeding goals or national benchmarks for breastfeeding success [17, 18]. Gold and Vander Weg discovered a significant relationship between parental weight stigma and feeding practices[19]. This suggested that parents who had experienced or internalized weight stigma might have adopted feeding strategies that were markedly different from those of parents without such experiences, potentially leading to restrictive feeding practices or impacting their ability to achieve breastfeeding goals. This effect may help explain the association between higher pre-pregnancy body mass index (BMI) and lower rates of breastfeeding. Indeed, higher BMI and accompanying internalized weight bias may lead some women to be less comfortable and self-efficacious when breastfeeding with others present or in public due to the increased focus and awareness of the stigma, which might be accompanied by negative thoughts and emotions [10, 17]. Furthermore, De Jager et al. found that lower breastfeeding self-efficacy mediated the relationship between perceived weight and shorter exclusive breastfeeding duration [20]. Despite these insights, there remains a notable lack of research exploring the role of weight stigma in the relationship between pre-pregnancy overweight/obesity and poor exclusive breastfeeding outcomes. This gap in the literature highlights an important area for further study.

Additionally, qualitative research from both healthcare providers and obese women themselves has indicated that women with pre-pregnancy overweight/obesity frequently face multiple challenges with breastfeeding that are either unique or exacerbated by their obesity [21, 22]. Two quantitative studies revealed that compared to their normal-weight counterparts, women with pre-pregnancy overweight/obesity experienced significantly greater challenges with breastfeeding during their postpartum hospital stay, as well as at 1 and 3 months postpartum, and this disparity contributed to their notably lower rates of breastfeeding [23, 24]. Moreover, O'Sullivan et al. found that early challenges linked to inadequate milk supply could elucidate the correlation between obesity and suboptimal exclusive breastfeeding outcomes [11]. Prior investigations have identified distinct obstacles that pre-pregnancy overweight/obese women face during breastfeeding, such as the delayed initiation of lactogenesis II, increased breast size, flattened nipples, challenges with infant breast positioning, and ineffective latch [25-27]. These issues may undermine the breastfeeding self-efficacy of women with pre-pregnancy overweight/obesity. Nonetheless, there remains a significant gap in the research regarding the use of quantitative tools to evaluate specific breastfeeding difficulties experienced by this demographic. Frequently, research aggregated these issues into an overall construct of “breastfeeding difficulties,” largely derived from maternal self-reports of “Yes” or “No.” To date, no research has examined the relationship between upstream factors such as breastfeeding difficulties and IWS, and their impact on breastfeeding self-efficacy. Additionally, data are scarce regarding how these factors affect breastfeeding behaviors among women with pre-pregnancy overweight/obesity.

Taken together, the present study aimed to examine: (1) whether pre-pregnancy overweight/obesity is associated with lower rates of exclusive breastfeeding at 6 months, and (2) whether IWS, breastfeeding difficulties, and breastfeeding self-efficacy mediate the relationship between pre-pregnancy overweight/obesity and exclusive breastfeeding at 6 months, both independently and sequentially, to identify modifiable factors that may serve as intervention targets. Based on objectification theory and literature review, we proposed the following hypotheses: first, pre-pregnancy overweight/obesity would be negatively linked to exclusive breastfeeding at 6 months (H1). Second, the negative link from pre-pregnancy overweight/obesity to exclusive breastfeeding at 6 months would be mediated by IWS (H2), breastfeeding difficulties (H3), and breastfeeding self-efficacy (H4). Third, the negative relationship between pre-pregnancy overweight/obesity and exclusive breastfeeding at 6 months would be mediated by IWS and breastfeeding self-efficacy serially (H5). Fourth, the negative relationship would be serially mediated by breastfeeding difficulties and breastfeeding self-efficacy (H6). The proposed conceptual model is shown in Fig. 1.

2.1 Participants and procedure

In this prospective cohort study, two members of the research team recruited 320 pregnant women with singleton pregnancies at 35–37 weeks of gestation during their scheduled prenatal visits between September 2022 and March 2023 at Nanjing Maternity and Child Health Care Hospital. This hospital, designated as "baby-friendly" since 1993, delivers approximately 24,800 newborns annually. The inclusion criteria were as follows: women with a BMI of ≥18.5 kg/m² who expressed an intention to breastfeed, primiparas aged 20–35 years, and those who delivered healthy full-term newborns (≥ 37 weeks gestation). The exclusion criteria encompassed severe psychiatric illnesses, cardiovascular or pulmonary diseases, a history of breast surgery or injury, or a diagnosis of mammary dysplasia that could hinder the establishment of effective breastfeeding. All participants were followed for at least six months postpartum.

2.2 Measures

2.2.1 Independent variable

Pre-pregnancy BMI was directly obtained from the obstetric clinic’s system, and self-reported by the participants at their initial prenatal visit. Pre-pregnancy BMI was calculated as weight in kilograms divided by the square of height in meters (kg/m²) and classified according to Chinese standards into four categories: underweight (BMI < 18.5 kg/m²), normal BMI (BMI 18.5–23.9 kg/m²), overweight (BMI 24.0–27.9 kg/m²), and obese (BMI ≥ 28.0 kg/m²) [28]. For this study, participants were divided into two groups: normal BMI (BMI 18.5–23.9 kg/m²) and overweight/obese (BMI ≥ 24.0 kg/m²).

2.2.2 Dependent variables

The outcome analyzed in this study was exclusive breastfeeding up to 6 months postpartum. Exclusive breastfeeding status at this time point was assessed using a 7-day dietary recall method for infants, based on mothers’ self-reports concerning the frequency and amount of breastfeeding and formula milk supplementation. Infants solely receiving breast milk, with no intake of other solids or liquids over the previous 7 days, were classified as “exclusive breastfeeding.” Those who ingested any breast milk during the same timeframe were classified as “any breastfeeding.”

2.2.3 Potential mediating variables

2.2.3.1 IWS

IWS was assessed with the Weight Bias Internalization Scale (WBIS). WBIS offers a precise measure for assessing weight-bias internalization, clearly distinguishing this construct from anti-fat attitudes, self-esteem, and body image. This scale includes 11 items, each rated on a Likert scale ranging from 1 (strongly disagree) to 5 (strongly agree). Reverse coding of two specific items (items 1 and 9) is required before summing the scores, which total up to a maximum of 55. The WBIS exhibits satisfactory internal consistency, with a Cronbach’s alpha of 0.9. Higher aggregate scores indicate a more pronounced internalization of weight stigma [12]. The Chinese version of the WBIS modifies the term “overweight” to “weight” to better suit individuals across various weight statuses. For example, the item “I hate myself for being overweight” is adapted to “I hate myself because of my weight.” The Chinese version of the WBIS demonstrates robust internal consistency in research conducted with Chinese children, adolescents, and postpartum populations [29, 30].

2.2.3.2 Breastfeeding difficulties

Drawing from the Breastfeeding Problems Inventory utilized in the research by O'Sullivan et al. [11], this study evaluated the extent of maternal breastfeeding difficulties at 6 months postpartum. If the mother discontinued breastfeeding within the first 6 months postpartum, difficulties encountered during the final period of breastfeeding should be reported. The questionnaire, having undergone expert validation and preliminary surveys, has been adapted to reflect the clinical realities of breastfeeding in China. It comprises 17 questions across four dimensions: insufficient milk production, breast dysfunction, infant feeding difficulties, and excessive lactation. During the survey, mothers were asked, “In the past week, have you experienced any of the following problems while breastfeeding your infant?” They were directed to identify applicable issues from a list of 17 potential breastfeeding problems, scoring each on a binary scale: 1 for “yes” and 0 for “no.” The total possible score ranges from 0 to 17, with higher scores indicating greater breastfeeding challenges faced by the mother.

2.2.3.3 Breastfeeding self-efficacy

To assess breastfeeding self-efficacy, we utilized the Breastfeeding Self-Efficacy Scale-Short Form (BSES-SF), as developed by Dennis [31], which demonstrated excellent reliability with a Cronbach’s alpha of 0.927. This scale comprises 14 items, each scores on a 5-point Likert scale ranging from 1 (“completely lack confidence”) to 5 (“extremely confident”). Higher scores reflect greater self-efficacy in breastfeeding. The BSES-SF, which has undergone international validation, has been translated into multiple languages, such as Polish and Spanish [32, 33], with Cronbach’s alpha coefficients ranging from 0.85 to 0.95. The Chinese version of BSES-SF had good reliability and validity, with a Cronbach’s alpha coefficient of 0.927 [34].

2.2.4 Covariates

We utilized a multimodal data collection strategy encompassing structured interviews, self-administered questionnaires, and comprehensive review of medical records to assess confounders and precision variables. Sociodemographic variables were systematically recorded, including maternal age, educational attainment, employment status before pregnancy, household income, and gestational weight gain (GWG). We classified GWG as “inadequate”, “adequate”, or “excessive” according to the Institute of Medicine 2009 GWG guideline[35]. Postpartum data collection involved a detailed examination of medical records for each mother-infant dyad, documenting the mode of delivery, any complications arising during delivery, gestational age at birth, infant birth weight, and incidences of each mother-infant separation or neonatal complications.

2.3 Sample size estimation

We utilized Power Analysis & Sample Size (PASS) software version 15.0 (NCSS Statistical Software, LLC, Kaysville, UT, USA) to determine the required sample size, drawing on data from our previous study. In our previous study, the exclusive breastfeeding rate at 6 months postpartum was 14.0% among the overweight/obese group and 34.0% in the normal-BMI group. To ensure robust statistical power, we recruited women with pre-pregnancy overweight/obesity and normal BMI in a 1:1 ratio, targeting 90% power at a 5% significance level, and accounting for a potential 20% attrition rate. Consequently, a minimum of 89 participants per group was deemed necessary. Additionally, Kline suggested an acceptable sample size for studies using structural equation modeling (SEM), which is about 200 cases [36]. The sample for this study included 296 participants, exceeding both the previously determined sample size of 178 and the recommended threshold for SEM analysis.

2.4 Statistical analysis

We conducted primary analyses using SPSS version 25.0 (IBM Corp., Armonk, NY, USA). Preliminary analyses explored bivariate associations between pre-pregnancy overweight/obesity and other model variables. Our hypotheses were theoretically grounded and based on literature, and they were specified before data treatment. To test these hypotheses, we conducted SEM analyses using Mplus version 8.3.

This study aimed to clarify the mechanisms by which pre-pregnancy overweight/obesity, compared to women with normal BMI, influenced the rate of exclusive breastfeeding at 6 months postpartum. Pre-pregnancy BMI was considered as the independent variable (assigned as normal-BMI = 0, pre-pregnancy overweight/obesity = 1). IWS, breastfeeding difficulties, and breastfeeding self-efficacy were set as mediating variables. The binary outcome of exclusive breastfeeding at 6 months postpartum (non-exclusive = 0, exclusive = 1) served as the dependent variable. Using a multiple mediation model, we were able to uncover complex interaction pathways among variables, enhance the explanatory power of our analysis, and detect indirect effects through the interconnected influence of multiple mediators. We utilized SEM with maximum likelihood estimation, along with bias-corrected bootstrap testing provided by the Mplus 8.3 software package, to estimate and assess the mediation effects. Total effects (X on Y), direct effects (X on Y, adjusted for mediating effects), and specific indirect effects (X on Y through a specific mediator) were estimated with the use of a cumulative logistic regression-based, path-analytic framework. Mediation analyses incorporated a bias-corrected bootstrap method with 95% confidence intervals (CIs, 1,000 resamples) to estimate the magnitude of the total, direct, and indirect effects. The bootstrap method is the most extensively employed approach for directly testing the product of coefficients, ab, in mediation analysis. This method involves repeatedly drawing bootstrap samples and computing estimates of a and b, to derive the bootstrap 95% confidence interval for the product ab. If this confidence interval does not include zero, the mediating effect is deemed statistically significant; conversely, if the interval includes zero, the mediating effect is considered not significant. Furthermore, we controlled for the influence of potential confounders, such as gestational weight gain, mode of childbirth, comorbidity, and infant birth weight, in all mediation analyses. It should be noted, however, that the term “effect” referred to a statistical and not a causal effect in our mediation analysis.

3.1 Characteristics of the study participants

Fig. 2 illustrates the progression of participants from recruitment through to data analysis. Our study included a final sample of 296 mother-infant dyads, with Table 1 presenting the demographic and clinical characteristics of the groups. Compared to their normal-BMI counterparts, mothers in the pre-pregnancy overweight/obese group were significantly more likely to experience excessive weight gain during pregnancy (p < 0.001), display increased comorbidities (p = 0.017), and undergo cesarean sections (p = 0.004); correspondingly, their infants were born with significantly higher birth weights than those from the normal-BMI group (p < 0.001). Their BMIs at childbirth also remained significantly elevated in comparison to the normal-BMI group (p < 0.001). We found no significant differences between groups concerning maternal age, educational level, employment status, monthly per-capita household income, and gestational age (all p > 0.05). Furthermore, there were no significant differences in the demographic and clinical characteristics between the lost-to-follow-up group and the surveyed group (p > 0.05).

3.2 Analysis of IWS, breastfeeding difficulties, breastfeeding self-efficacy, and breastfeeding prevalence by pre-pregnancy BMI status

Compared with women showing a normal BMI, those with pre-pregnancy overweight/obesity exhibited a higher IWS, reported greater breastfeeding difficulties, and demonstrated reduced self-efficacy in breastfeeding, as detailed in Table 2. There was no discernible difference in postpartum depression rates between the pre-pregnancy BMI groups. By six months postpartum, 93.33% of women with a normal BMI and 79.97% of obese women were still breastfeeding. Among these, 40% of women with normal BMI and 13.7% of women with pre-pregnancy overweight/obesity were exclusively breastfeeding. Normal-BMI primiparous women were signiffcantly more likely to be exclusively breastfeeding at 6 months postpartum compared to their overweight/obese counterparts.

3.3 Primary analyses

We conducted the mediation analyses after adjusting for covariates. We assigned values to the binary variables of the mode of childbirth（vaginal = 0, cesarean = 1). The multiclass variables of GWG (assigned: inadequate = 0, adequate =1, excessive =2); and comorbidity (assigned: none = 0, gestational diabetes mellitus = 1, thyroid disease = 2, gestational hypertension = 3, postpartum hemorrhage = 4, other complications = 5) were pre-set as dummy variables.

3.3.1 Standardized path coefficients in the mediation analysis

As shown in Table 3, pre-pregnancy overweight/obesity reflected a significant positive impact on IWS (a₁, β = 0.654, p < 0.001) and breastfeeding difficulties (a₂, β = 0.306, p < 0.001). Conversely, we found that pre-pregnancy overweight/obesity was negatively associated with breastfeeding self-efficacy (a₃, β = −0.146, p = 0.015). Furthermore, breastfeeding difficulties was found to inversely affect breastfeeding self-efficacy at 6 months postpartum significantly (d₂, β = −0.493, p < 0.001). However, IWS did not demonstrate a significant negative impact on breastfeeding self-efficacy within the model (d₁, β = −0.080, p = 0.254). Moreover, both IWS (b₁, β = −0.332, p = 0.001) and breastfeeding difficulties (b₂, β = −0.255, p = 0.011) exhibited significant negative associations with exclusive breastfeeding outcomes at 6 months postpartum. Meanwhile, breastfeeding self-efficacy (b₃, β = 0.354, p < 0.001) was positively associated with exclusive breastfeeding outcomes at 6 months postpartum (Fig. 3).

3.3.2 Testing for the mediation effects

The adjusted mediation model, which accounted for covariates such as GWG, comorbidity, mode of childbirth, and infant birth weight, revealed a significant total negative effect of pre-pregnancy overweight/obesity on exclusive breastfeeding at 6 months postpartum (β = −0.431, 95% CI, −0.532 to −0.303, p < 0.001). Furthermore, the total indirect effect was significant (β = −0.419, 95% CI: −0.551 to −0.310, p < 0.001), with specific indirect pathways through IWS (β = −0.217, 95% CI: −0.377 to −0.107, p = 0.001), breastfeeding difficulties (β = −0.078, 95% CI: −0.148 to −0.020, p = 0.018), and breastfeeding self-efficacy (β = −0.052, 95% CI: −0.110 to −0.015, p = 0.025) being significant. Additionally, a sequential mediation effect was observed, where breastfeeding difficulties and breastfeeding self-efficacy played significant chain roles in mediating the relationship between pre-pregnancy overweight/obesity and exclusive breastfeeding at 6 months postpartum (β = −0.053, 95% CI: −0.091 to −0.027, p = 0.001). However, no evidence was found supporting a chained mediation involving IWS and breastfeeding self-efficacy (Table 4).

The adjusted analysis yielded a bias-corrected 95% bootstrapped CIs for the direct effect of pre-pregnancy overweight/obesity on exclusive breastfeeding at 6 months postpartum, ranging from −0.169 to 0.156, which included zero as detailed in Table 4. This lack of statistical significance indicated that the direct effect was not substantial. Consequently, our results suggested a fully mediated model, where the negative effect of pre-pregnancy overweight/obesity on exclusive breastfeeding was predominantly mediated through pathways involving IWS, breastfeeding difficulties, and an indirect path via breastfeeding self-efficacy (Fig. 3).

In this prospective cohort study, we established that compared to women with normal BMI, increased IWS, significant breastfeeding difficulties, and lower breastfeeding self-efficacy serve as mediators in the negative association between pre-pregnancy overweight/obesity and exclusive breastfeeding at 6 months postpartum among primiparous women. IWS, stemming from sociocultural influences, along with breastfeeding difficulties and reduced self-efficacy, collectively elevate the risk of early cessation of exclusive breastfeeding in women with pre-pregnancy overweight/obesity. This suggests that interventions targeting these psychosocial and behavioral aspects, rather than focusing solely on body weight, may offer a more effective strategy for enhancing breastfeeding outcomes.

4.1 The mediating effect of IWS

As hypothesized, IWS served as a significant indirect mediating factor in the association between pre-pregnancy overweight/obesity and the practice of exclusive breastfeeding for 6 months. Few prior studies have directly examined the association between weight stigma internalization and breastfeeding among pre-pregnancy overweight/obese women. Contrary to our findings, Dieterich et al. reported that IWS did not influence breastfeeding behavior in their sample [37]. However, previous research has demonstrated that individuals with higher body weight often experience weight stigma and receive unequal breastfeeding support from healthcare professionals, which may impact breastfeeding behavior and outcomes [21, 30, 38]. Internalized stigmatization may deter breastfeeding efforts in women with pre-pregnancy overweight/obesity through several direct and indirect mechanisms. These include blame directed at obese women by healthcare professionals and inadequate postpartum care and support, which may hinder effective communication and the establishment of a harmonious doctor-patient relationship [39]. The presence of weight stigma in the medical environment can affect pre-pregnancy overweight/obese women’s willingness to seek breastfeeding support, ask feeding-related questions, and discuss their concerns about infant care [21, 40]. Additionally, IWS may undermine parental breastfeeding goals and efforts by being associated with perinatal mood disorders. Research indicated that experiencing weight stigma during pregnancy was linked to the onset of postpartum depressive symptoms within the first month following childbirth [17]. These depressive symptoms, in turn, were correlated with an increased risk of discontinuing breastfeeding at both 4 and 8 weeks postpartum [41]. Furthermore, postpartum depressive symptoms were associated with diminished breastfeeding self-efficacy, which further correlated with lower initiation rates and shorter durations of both any and exclusive breastfeeding [42, 43]. Despite these established associations, we did not reveal any significant difference in postpartum depression scores between the groups, nor did we uncover a sequential mediating effect of IWS and breastfeeding self-efficacy between pre-pregnancy overweight/obesity and exclusive breastfeeding outcomes in this study. These findings suggest the need for more detailed investigation in future research to explore these complex relationships further. Furthermore, although not addressed in the current study, it is crucial to note that IWS during pregnancy and postpartum may also indirectly affect breastfeeding outcomes through biophysical stress mechanisms. Research has shown that IWS functions as a physiological stressor, leading to elevated cortisol levels [44]. Maternal cortisol can be transferred from plasma to breast milk and hair [45]. Several studies have identified an association between cortisol levels in breast milk and infant behavior, potentially causing infants to be irritable, restless, and less likely to successfully latch during breastfeeding [46]. Additionally, maternal anxiety and elevated hair cortisol levels were positively correlated with delayed lactogenesis, indicating that both perceived and biophysical stress contributed to delayed milk production in postpartum individuals [47]. This issue is particularly concerning for individuals with a higher BMI, as they are already at an increased risk of delayed lactogenesis, irrespective of maternal biopsychosocial stress [27]. Nonetheless, the influence of cortisol levels as a potential factor influencing the relationship between IWS and subsequent breastfeeding behaviors remains unexamined. Future research should investigate the biological correlates of IWS to provide a more comprehensive understanding of its impact on breastfeeding behaviors.

4.2 The mediating effect of breastfeeding difficulties

This study found that breastfeeding difficulties were a key mechanism through which pre-pregnancy overweight/obesity affected exclusive breastfeeding rates at 6 months postpartum, compared to those of women with a normal BMI. Women with pre-pregnancy overweight/obesity had significantly higher breastfeeding difficulty scores than those with normal BMI at 6 months postpartum. Breastfeeding difficulties directly affected the rate of exclusive breastfeeding at 6 months postpartum, and additionally, they exerted an indirect influence on this rate through a chain-mediated effect on breastfeeding self-efficacy. Previous qualitative studies have shown that overweight/obese women face numerous breastfeeding challenges [21, 22]. These women reported concerns such as the risk of infant suffocation due to larger breasts, difficulties with infant positioning and latch-on, sucking issues, and trouble finding appropriate nursing bras. These challenges can undermine their confidence and breastfeeding self-efficacy, thereby impacting their ability to initiate and maintain exclusive breastfeeding [21, 48]. Besides, evidence suggested that some healthcare professionals may not recognize overweight/obesity as risk factors for adverse breastfeeding outcomes, which reduced the likelihood of offering additional support to these mothers [49]. This lack of awareness could contribute to the persistent breastfeeding challenges experienced by overweight/obese women, ultimately impacting their exclusive breastfeeding success and maintence. Moreover, in a case-control study, Mok et al. found that obese women (56.7%) experienced significantly higher rates of breastfeeding difficulties during hospitalization compared to women with normal pre-pregnancy weight (13.3%) [23]. Similarly, a large retrospective cohort study identified that obese women were significantly more likely to experience nipple pain, cracking, or bleeding, which were factors contributing to breastfeeding cessation among American women [50]. In contrast to previous studies that focused solely on specific types of breastfeeding difficulties or relied on subjective reports from obese mothers, our research utilized the breastfeeding problem checklist, as used in the study by O'Sullivan et al. [11]. By analyzing the yes/no responses provided by the participants and scoring these difficulties, we were able to quantitatively evaluate the severity of breastfeeding challenges faced by overweight and obese women. However, currently, there is a dearth of reliable clinical instruments for evaluating and predicting breastfeeding difficulties. Future developments in this area are necessary to equip healthcare professionals with the tools to proactively devise care plans for pre-pregnancy overweight/obese women, addressing potential difficulties in breastfeeding both in hospital and home settings.

4.3 The mediating effect of breastfeeding self-efficacy

As expected, our study revealed that breastfeeding self-efficacy was a significant mediating factor in the negative association between pre-pregnancy overweight/obesity and exclusive breastfeeding at 6 months. Breastfeeding self-efficacy reflects a mother’s confidence in breastfeeding and is a modifiable factor that can potentially improve breastfeeding rates [51]. However, there is a paucity of studies exploring the determinants of low breastfeeding self-efficacy among mothers with pre-pregnancy overweight/obesity. We speculate that several factors may contribute to this issue. For instance, our results, along with those of several other authors, indicated that women with higher pre-pregnancy BMIs were more likely to report greater breastfeeding difficulties [24, 26]. Additionally, mothers were not be adequately prepared for the breastfeeding challenges they encountered after childbirth, which could be related to lower breastfeeding self-efficacy in this population. Moreover, various psychological disturbances experienced during the postpartum period may further compromise breastfeeding self-efficacy. Previous research has established a correlation between obesity and adverse mental health outcomes during the perinatal period [52]. Although our study did not observe significant differences in postpartum depression across pre-pregnancy BMI categories at 6 months postpartum, other psychological factors, particularly in the early weeks postpartum, may explain the mediating role of breastfeeding self-efficacy in the association between pre-pregnancy overweight/obesity and less favorable exclusive-breastfeeding outcomes. Therefore, it is imperative to identify the determinants of breastfeeding self-efficacy among women with pre-pregnancy overweight/obesity, as this remains a critical area for future investigation.

4.4 Limitations and implications

Several limitations of this study warrant careful consideration. First, our sample, drawn from a single large general hospital in China, presented a homogeneous demographic profile, potentially limiting the generalizability of our findings. Second, this study only analyzed longitudinal data at a single follow-up point, making it unfeasible to draw clear causal inferences. Future research should employ longitudinal studies with data collected at multiple time points and incorporate experimental approaches to more effectively elucidate the causal relationships between variables. Third, in this study, those with high pre-pregnancy BMI who lack breastfeeding intentions were excluded from the study population. However, this group also represents a potential target for breastfeeding interventions. The mechanisms influencing their intentions to breastfeed and their final breastfeeding decisions are worth further in-depth exploration. Additionally, approximately 30% of women with pre-pregnancy overweight/obesity ceased breastfeeding by 6 months postpartum. This observation highlights the urgent need to explore the mechanisms by which pre-pregnancy overweight/obesity influences breastfeeding duration, to enhance clinical intervention strategies. More importantly, despite our study being grounded in theory and literature review, we could not completely dismiss the mediating roles of unmeasured variables. Potential future directions include tracking breastfeeding status and duration at multiple time points and beyond 6 months postpartum, evaluating additional heterogeneous samples, and exploring ancillary mediating factors, given that the intricacies of these relationships are not yet comprehensively understood.

Despite its limitations, the current study offers several implications. It addresses gaps in the existing research within the Chinese context and enhances our understanding of how pre-pregnancy overweight/obesity correlates with lower rates of exclusive breastfeeding by testing the mediating roles of IWS, breastfeeding difficulties and breastfeeding self-efficacy. Although healthcare workers are not the only source of weight stigma, studies have shown that such stigma is prevalent among medical students, healthcare professionals, and even researchers specializing in obesity studies. Therefore, our research underscores the need to take proactive steps to enhance internal management within healthcare facilities. This includes developing policies and educational materials specifically aimed at training clinical staff about weight stigma. By deepening their understanding of its detrimental effects and aiding in the identification of its sources, these initiatives are critical for establishing a discrimination-free, safe, supportive, and respectful environment for pregnant and postpartum women. Furthermore, enhancing the training and education of medical personnel is essential to increase their awareness and understanding of the unique breastfeeding challenges faced by pre-pregnancy overweight or obese mothers. Special attention must be given to the timing and substance of the support provided to these women, addressing potential feelings of shame and embarrassment to facilitate effective, tailored breastfeeding support. To further improve these women's breastfeeding self-efficacy, it is crucial to implement comprehensive, multifaceted educational programs that not only educate about breastfeeding techniques but also reinforce the psychological support necessary to bolster confidence and resilience in breastfeeding.

This study revealed a negative correlation between pre-pregnancy overweight/obesity and exclusive breastfeeding at 6 months postpartum. This relationship was mediated by factors such as IWS, breastfeeding difficulties, and breastfeeding self-efficacy, each impacting the outcome both individually and in sequence. These findings highlight the urgent clinical need to address weight stigma and enhance support for breastfeeding among women with pre-pregnancy overweight/obesity. It is imperative for healthcare professionals to practice unbiased medical care, employing inclusive language and providing customized breastfeeding support. Moreover, educating mothers on effective breastfeeding techniques, resolving lactation issues, and strengthening self-efficacy are essential strategies. By concentrating on these critical areas, we can shape public health strategies and clinical practices that are specifically designed to address the obesity-related breastfeeding challenges, thereby significantly enhancing exclusive breastfeeding rates.

WHO: World Health Organization; BMI: Body mass index; IWS: Internalized weight stigma; WBIS: Weight Bias Internalization Scale; BSES-SF: Breastfeeding Self-Efficacy Scale-Short Form; GWG: Gestational weight gain; PASS: Power Analysis & Sample Size; SEM: Structural equation modeling; CIs: Confidence intervals; SD: Standard deviation; GWG = Gestational weight gain; GDM = Gestational diabetes mellitus; BF: breastfeeding; EBF: exclusive breastfeeding; ABF: any breastfeeding; SE: standard estimate; LLCI: Lower limit of confidence interval; ULCI: Upper limit of confidence interval.

Ethics approval and consent to participate

This study was conducted in accordance with the Declaration of Helsinki and approved by the Ethics Committee of Nanjing Maternity and Child Health Care Hospital (2021KY-085). All procedures complied with relevant laws and institutional guidelines. The privacy rights of human subjects were protected, and all participants provided informed consent before completing the initial questionnaire. As a token of appreciation for their valuable contribution, each participant received a one-time child healthcare guidance session after completing the survey.

Consent for publication

Not Applicable.

Data Available Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Declaration of competing interest

The authors declare that they have no conflict of interest concerning the research, authorship, and/or publication of this article.

Funding

This work was supported by the Funding of Nursing Scientific Research at Fudan University [grant number: FNF202102] and the National Natural Science Foundation of China Youth Program (grant number: 72204123).

Author Contributions

ZQR contributed to the conceptualization, methodology, investigation, data curation, analysis, and interpretation; drafted and critically revised the manuscript; and took responsibility for the integrity of the data and the accuracy of the data analysis. HTT managed the conceptualization, participants’ recruitment, investigation, data curation, and manuscript revision. XMF and JYF handled the participants’ recruitment, data curation, and the review and editing of the manuscript. AXZ directed the methodology, manuscript drafting and revision, study supervision, and gave final approval of the version to be submitted.

Acknowledgments

We extend our heartfelt gratitude to the doctors and nurses of the Department of Obstetrics at the Nanjing Maternity and Child Health Care Hospital for their invaluable support and cooperation during specimen collection. We are also deeply appreciative of all the participants and their caregivers for their assistance with this study. Special thanks are owed to Jiejing Sheng from the Hospital of Obstetrics and Gynecology, Fudan University, for the expert guidance on breastfeeding.

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Table 1 Demographic and clinical characteristics of the included participants and their infants by pre-pregnancy BMI category

Characteristics	Maternal pre-pregnancy BMI category			t^a/Χ²^b/Z^c	p value
Characteristics	Normal BMI (n =150)	Overweight/obese (n = 146)
Maternal age, mean (SD), y	28.86 ± 2.93		29.52 ± 3.39	−1.796^a	0.074
Pre-pregnancy BMI, mean (SD), kg/m²	20.85 ± 1.52		29.96 ± 3.47	14.873^c	<0.001^**
Maternal BMI at childbirth, kg/m²	25.81 ± 2.04		34.60 ± 3.74	14.723^c	<0.001^**
GWG, no. (%)
Inadequate	16 10.67)		15 (10.27)	29.352^b	<0.001^**
Adequate	80 (53.33)		35 (23.97)
Excessive	54 (36.00)		96 (65.75)
Educational level, no. (%)
≤ Junior high school	1 (0.67)		3 (2.05)	5.928^b	0.106
High school/technical secondary school	14 (9.33)		14 (9.59)
Associates degree/some college	111 (74.00)		118 (80.82)	1.160^b	0.345
≥ Graduate degree	24 (16.00)		11 (7.53)
Employment status, no. (%)
Employed	117 (78.00)		106 (72.60)
Unemployed/paid leave	33 (22.00)		40 (27.40)
Monthly per-capita household income (RMB), no. (%)
≤3000	1 (0.67)		3 (2.05)	1.231^b	0.534
3000–5000	32 (21.33)		34 (23.29)
≥5000	117 (78.00)		109 (74.66)
Comorbidity, no. (%)
GDM	38 (25.33)		48 (32.88)	13.449^b	0.017^*
Thyroid dysfunction	14 (9.33)		13 (8.90)
Gestational hypertension	6 (4.00)		11 (7.53)
Postpartum hemorrhage	4 (2.67)		7 (4.79)
Other comorbidities	12 (8.00)		1 (0.68)
None	76 (50.67)		66 (45.21)
Mode of childbirth, no. (%)
Vaginal	106 (70.67)		79 (54.11)	8.654^b	0.004^*
Caesarean	44 (29.33)		67 (45.89)
Gestational age, mean (SD), w	39.76 ± 1.01		39.72 ± 1.04	0.380^a	0.704
Infant birth weight, mean (SD), g	3341.20 ± 405.16		3533.42 ± 468.00	−3.781^a	<0.001^**

Notes: ^aIndependent-sample t-test; ^bChi-squared/Fisher’s exact test; ^cMann–Whitney U test.

Abbreviations: BMI = body mass index; SD = standard deviation; GWG = gestational weight gain; GDM = gestational diabetes mellitus. ^*p < 0.05; ^**p < 0.001.

Table 2 IWS, Breastfeeding Difficulties, and Breastfeeding Self-Efficacy variables and prevalence of breastfeeding outcomes at 6 months postpartum by pre-pregnancy BMI category

Variables	Maternal pre-pregnancy BMI category		t^a/Χ²^b/Z^c	p value
Variables	Normal BMI (n = 150)	Overweight/obese (n = 146)
IWS, mean (SD), score	22.42 ± 3.75	30.73 ± 5.71	11.584^c	<0.001^**
BF difficulties, mean (SD), score	2.47 ± 1.56	3.76 ± 2.40	4.868^c	<0.001^**
BF self-efficacy, mean (SD), score	55.08 ± 8.53	48.21 ± 10.05	−5.379^c	<0.001^**
Postpartum depression, mean (SD), score	5.85 ± 3.47	6.40 ± 3.50	−1.360^a	0.175
Outcome, no. (%)
EBF at 6 months postpartum	60 (40.00)	20 (13.70)	25.951^b	<0.001^**
ABF at 6 months postpartum	140 (93.33)	108 (73.97)	20.412^b	<0.001^**
Artificial feeding at 6 months postpartum	10 (6.67)	38 (26.03)

Notes: ^aIndependent-sample t-test; ^bChi-squared/Fisher’s exact test; ^cMann–Whitney U test.

Abbreviations: IWS = internalized weight stigma; BMI = body mass index; SD = standard deviation; BF = breastfeeding; EBF = exclusive breastfeeding; ABF = any breastfeeding. ^*p < 0.05; ^**p < 0.001.

Table 3 Path coefficients in adjusted mediation models of the association between pre-pregnancy overweight/obesity and EBF at 6 months postpartum

Paths	Point estimate	t/Z	p value
Pre-pregnancy overweight/obesity to mediator
a₁, IWS	0.654	22.948	<0.001^**
a₂, BF difficulties	0.306	6.243	<0.001^**
a₃, BF self-efficacy	−0.146	−2.440	0.015^*
Mediator to EBF at 6 months postpartum
b₁, IWS	−0.332	−3.306	0.001^*
b₂, BF difficulties	−0.255	−2.551	0.011^*
b₃, BF self-efficacy	0.354	4.426	<0.001^**
Mediator to BF self-efficacy
d₁, IWS	−0.080	−1.141	0.254
d₂, BF difficulties	−0.493	−9.405	<0.001^**

Notes: Abbreviations: EBF = exclusive breastfeeding; IWS = internalized weight stigma; BF = breastfeeding.

^*p < 0.05; ^**p < 0.001.

Table 4 Mediation analysis results of the association between pre-pregnancy overweight/obesity (X) and EBF at 6 months postpartum (Y）

Type of effect (paths)	Point estimate	Boot SE	Boot 95%CI		p value
Type of effect (paths)	Point estimate	Boot SE	LLCI	ULCI	p value
Total effect	−0.431	0.058	−0.532	−0.303	<0.001^**
Direct effect	−0.012	0.084	−0.169	0.156	0.886
Total indirect effect	−0.419	0.060	−0.551	−0.310	<0.001^**
Pre-pregnancy overweight/obesity→IWS→EBF at 6 months postpartum	−0.217	0.066	−0.377	−0.107	0.001^*
Pre-pregnancy overweight/obesity→BF difficulties→EBF at 6 months postpartum	−0.078	0.033	−0.148	−0.020	0.018^*
Pre-pregnancy overweight/obesity→BF self-efficacy→EBF at 6 months postpartum	−0.052	0.023	−0.110	−0.015	0.025^*
Pre-pregnancy overweight/obesity→IWS→BF self-efficacy→EBF at 6 months postpartum	−0.019	0.019	−0.067	0.009	0.315
Pre-pregnancy overweight/obesity→BF difficulties→BF self-efficacy→EBF at 6 months postpartum	−0.053	0.016	−0.091	−0.027	0.001^*

Notes: Abbreviations: EBF = exclusive breastfeeding; SE = standard estimate; LLCI = lower limit of confidence interval; ULCI = upper limit of confidence interval; IWS = internalized weight stigma; BF = breastfeeding. ^* p < 0.05; ^** p < 0.001.

No competing interests reported.

The Multiple Mediating Effects of Internalized Weight Stigma, Breastfeeding Difficulties, and Breastfeeding Self-Efficacy on the Association Between Pre-pregnancy Overweight/Obesity and Exclusive Breastfeeding at 6 Months Postpartum: A Prospective Cohort Study

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Abstract

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1. Introduction

2. Methods

3. Results

4. Discussion

5. Conclusions

Abbreviations

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References

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