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. Author manuscript; available in PMC: 2024 Jan 1.
Published in final edited form as: J Contextual Behav Sci. 2022 Nov 24;27:11–15. doi: 10.1016/j.jcbs.2022.11.005

Examining psychological inflexibility as a mediator of postpartum depressive symptoms: A longitudinal observational study of perinatal depression

Emily B K Thomas 1, Michelle L Miller 2, Rebecca Grekin 1,3, Michael W O’Hara 1
PMCID: PMC9770600  NIHMSID: NIHMS1853803  PMID: 36570435

Abstract

Background:

Depression is a common, serious complication during the postpartum period. Predictors of postpartum depression characterize who is at-risk for persistent symptoms. This study explored how psychological inflexibility affects depressive symptoms at 4 and 12 weeks postpartum.

Methods:

Participants receiving prenatal care at a medical center were recruited during the second trimester. Participants (n = 180) completed online assessments and diagnostic interviews during the third trimester (≥ 28 weeks gestation), and at 4-, 8-, and 12-weeks postpartum. Online assessments measured psychological inflexibility (PI) and depressive symptoms, while diagnostic interviews measured lifetime history of depression.

Results:

Mediation analysis examined pathways between 4-weeks postpartum depression, 8-weeks postpartum PI, and 12-weeks postpartum depression. Depressive symptoms at 4-weeks postpartum predicted PI at 8-weeks postpartum (β = 0.31, SE = 0.06, t(177) = 6.06, p < .001). Depressive symptoms at 4-weeks postpartum (β = 0.42, SE = 0.06, t(176) = 7.12, p < .001) and PI at 8-weeks postpartum (β = 0.32, SE = .08, t(176) = 4.09, p < .001) predicted depressive symptoms at 12-weeks postpartum. Depressive symptoms at 4-weeks, 8-week PI, and lifetime history of depression accounted for 42% of the variance in 12-week depressive symptoms (R2 = 0.42). The confidence interval of the indirect effect (0.04, 0.18) did not include zero, indicating significant mediation by PI.

Conclusions:

PI mediated the relation between 4- and 12-weeks postpartum depressive symptoms when controlling for lifetime history of depression. Psychological inflexibility is a transdiagnostic target for future prevention and intervention research during the postpartum period.

Keywords: postpartum depression, psychological inflexibility, perinatal period, longitudinal, mediation

Introduction

Depression is one of the most common medical complications of the perinatal period (pregnancy through 12 months postpartum), affecting approximately one in five women (O’Hara & McCabe, 2013). Importantly, the costs of perinatal depression are life-encompassing and include increased distress in mothers and families, impairment in daily functioning, comorbid anxiety, mother-infant bonding difficulties, and increased risk for emotional and behavioral disorders in offspring (Beebe et al., 2008; Henrichs et al., 2010; Li et al., 2009; O’Donnell et al., 2014). Despite these costly outcomes, barriers remain in adequately identifying, assessing, and treating those at-risk.

A particularly cumbersome hurdle in addressing perinatal mental health is the time interval specifier for perinatal depression in the current iteration of the DSM (Diagnostic and Statistical Manual of Mental Disorders (DSM-5-TR®), 2022), wherein the perinatal specifier is identified as during pregnancy or in the first 4 weeks postpartum. Conversely, clinicians and researchers define the postpartum period as the first 12 months following delivery, rather than the first 4 weeks, as a period of increased vulnerability of onset/exacerbation of depressive, anxiety, OCD, and psychosis symptoms (Kroska & Stowe, 2020). Given this discrepancy in diagnostic and research definitions, it is important to identify predictors of depressive symptoms that persist beyond the 4-week postpartum window to understand who may be most at-risk for persistent symptoms. Moreover, these differing definitions lack clarity for patients, providers, and systems as they navigate how to screen for and treat perinatal mood and anxiety symptoms. Identifying predictors early in the postpartum period is critical so that we can more efficiently treat mothers who are suffering during this critical familial developmental period.

A recent review summarized the last decade of research regarding predictors of postpartum depression (Guintivano et al., 2018), including static predictors such as race, history of depression, trauma history, and age. However, increasing literature has identified modifiable processes in the postpartum period. For example, negative affect present within the first three days postpartum predicted depression at 12 weeks postpartum (Miller et al., 2017). Determining modifiable and transdiagnostic processes early in the postpartum period will allow for more targeted psychotherapeutic interventions that can reduce risk.

One such modifiable process may be psychological inflexibility (PI), defined as rigid response patterns to internal experiences (e.g., thoughts, emotions, memories, urges), resulting in dominance of avoidant versus values-based behaviors (S. C. Hayes et al., 2006). PI has been shown to be a psychological process underlying a spectrum of emotional disorders, like major depression, anxiety, and substance use (Levin et al., 2014). PI is increasingly being studied as an important variable in maternal health. One study examined PI among mothers of medically vulnerable infants, finding that PI mediated the relation between early and later maternal postpartum depressive symptoms (Stotts et al., 2019). Furthermore, experiential avoidance, a facet of PI, was found to be the strongest predictor of maternal depressive and anxiety symptoms in a hierarchical regression analysis including infant birth weight, experiential avoidance, relationship satisfaction, prenatal expectations, and postpartum support (Evans et al., 2012). Experiential avoidance has also been shown to mediate the relation between dysfunctional beliefs about motherhood and postpartum depressive and anxiety symptoms (Fonseca et al., 2018). The extant literature provides strong indications that psychological inflexibility and its components are important and modifiable therapeutic processes that are likely important in the maintenance of perinatal psychopathology. Notably, many of the studies utilized self-report measures to characterize the sample’s psychiatric symptoms, whereas diagnostic interviews are optimal for measurement of psychopathology.

The current study aimed to expand upon the current literature by examining what role PI plays in maintaining depressive symptoms across the postpartum period while controlling for history of depression. We assessed participants during pregnancy and throughout the postpartum period at 4-, 8-, and 12-weeks postpartum. Given that the DSM-5-TR denotes the peripartum period as ending at 4-weeks postpartum, we examined whether PI at 8-weeks postpartum mediated the relation between 4- and 12-week depressive symptoms. Importantly, most postpartum medical visits occur during the early postpartum period (usually at 6 weeks, with new initiatives to include 1-, 3-, and 12-week visits). Identifying malleable risk factors for depression that can be identified early in the postpartum period could translate to implementing interventions for postpartum women at times they are most likely to interact with healthcare. Moreover, this would offer potential to expand options for integrated care (e.g., warm handoffs while the woman is physically in the clinic). Additionally, the measurement time periods chosen were consistent with the limited literature. One study measured depressive symptoms and PI in a sample of postpartum women whose infants had been admitted to the neonatal intensive care unit (NICU; Stotts et al., 2019). Depressive symptoms were measured 1-2 weeks after delivery and NICU admission and again at 2-3 months postpartum; PI was measured at 2-weeks postpartum. PI was found to mediate the relation between depressive symptoms at baseline and 2-3-month follow-up. However, measurement dates corresponded with infant discharge from the NICU and weeks postpartum. Utilizing similar time points among a community sample, rather than a sample of mothers of medically vulnerable infants, was intended to provide further evidence as to the relation between depressive symptoms and PI. We hypothesized that higher levels of PI at 8-weeks postpartum would mediate a positive relation between depressive symptoms at 4- and 12-weeks postpartum in a community sample.

Method

Participants

The current sample was drawn from a larger study wherein participants were recruited in their third trimester of pregnancy, who received their prenatal care at a large hospital in the midwestern United States of America. Participants were primarily White, highly educated, high-income, and married or cohabitating. Given that this study focused on postpartum depressive symptoms, eligible participants completed the first postpartum assessment at 4-weeks postpartum (n = 231). Moreover, 4 participants did not complete the diagnostic assessment, and as such, were not included in the analyses (n = 227). Attrition was observed between time points, with 201 participants completing the 8-weeks postpartum assessment, and 201 participants completing the 12-weeks postpartum assessment. Note that some participants opted to respond to one assessment time point and not others, meaning that the 201 participants at the 8- and 12- week timepoints were comprised of somewhat different individuals. As such, only the 180 participants who completed all postpartum time points, as well as the psychiatric interview during pregnancy, were included in the mediation analysis. To determine whether there were demographic differences between those who responded to all assessments and those who did not, we conducted preliminary analyses to compare these groups. The groups did not differ in terms of age, t(216) = 0.88, p = 0.38. The groups differed in third trimester depressive symptoms, t(228) = −2.40, p = 0.02, with those who completed all assessments reported lower depressive symptoms (M = 34.40, SD = 8.20) than those who did not (M = 38.20, SD = 14.60). Excluding those (n = 4) who did not complete the structured interview, no differences were observed between completers and non-completers in history of depression, X2(1) = 0.51, p = 0.47. There were no differences in education level between completers and non-completers, X2(3) = 5.45, p = 0.14, nor income level, X2(2) = 2.15, p = 0.34. Given insufficient sample size for racial, ethnic, and marital status in some groups, comparisons were not able to be reliably conducted between completers and non-completers as related to these variables.

Study Procedures

All study procedures were approved by the University’s Institutional Review Board. Female patients who were pregnant between April and December 2015 were identified by the Institute for Clinical and Translational Science and sent informational letters near 28-weeks gestation. Unless they initially declined participation, potential participants were contacted to determine interest in the study. Research staff confirmed eligibility (28-32-weeks gestation, ≥18 years old) and mailed a consent form, which was reviewed by telephone. Written informed consent was obtained before study procedures began in compliance with the IRB protocol.

Assessment Procedures

Participants completed online assessments and diagnostic interviews during the third trimester (starting at 28-weeks gestation), and at 4-, 8-, and 12-weeks postpartum. Data collection and management was conducted using REDCap electronic data capture, hosted at the University of Iowa (Research Electronic Data Capture; Harris et al., 2009). REDCap is a secure, web-based application designed to support longitudinal data capture for research studies.

Measures

Depressive symptoms.

The Inventory of Depression and Anxiety Symptoms – General Depression Scale (IDAS-GD; Watson et al., 2007, 2008) is a 20-item self-report measure that assesses depressive symptoms over the past two weeks. Participants are asked to rate each item on a 5-point scale (1 = not at all to 5 = extremely). Higher scores indicate more severe depressive symptoms. Coefficient alpha for the current study was good at 4-weeks (α = 0.91) and 12-weeks postpartum (α = 0.86).

Lifetime history of depression.

The Structured Clinical Interview for DSM-5 Disorders (SCID-5; First et al., 2016) SCID is a well-validated, semi-structured interview for assessing DSM-5 diagnoses. The Major Depression module was administered during pregnancy to measure lifetime history and current depression. History of depression was quantified categorically for presence or absence of current or past depression. Other modules of the SCID were administered but not included in the present analyses, including mania, obsessive-compulsive disorder, and posttraumatic stress disorder.

Psychological inflexibility.

The Acceptance and Action Questionnaire – II (AAQ-II; Bond et al., 2011) is a seven-item self-report measure that assesses psychologically inflexible responding to aversive internal experiences. Participants are asked to rate how true each statement is in their experience on a 7-point scale (1 = never true to 7 = always true). Higher scores indicate more psychologically inflexible responding. The questionnaire has established construct validity and internal consistency in prior work (Bond et al., 2011), but the limitations of this measure in assessing all aspects of psychological inflexibility have been noted (Ong et al., 2019; Tyndall et al., 2019). Notably, at the time of data collection, some of the more recent measures that assess multiple facets of ACT processes (for example, see (Francis et al., 2016)) were not yet published. Internal consistency of the AAQ-II in the current sample was adequate (α = 0.90).

Statistical Analyses

Analyses were conducted in SPSS, version 27, using the PROCESS macro (A. F. Hayes, 2022). Preliminary analyses examined outliers. If identified, outliers were examined for valid responding and data coding errors. No outliers were excluded from analyses, as the primary reason was high levels of symptoms among a community sample with generally lower symptom severity. Item-level missing data were imputed using person-mean if ≥80% of the items were complete on the scale. Descriptive characteristics of the sample are reported in Table 1.

Table 1.

Sample characteristics, n = 231

Variable Frequency (%)
Race, n = 227
American Indian/Alaska Native 1 (0.4%)
Asian 6 (2.6%)
Native Hawaiian or Pacific Islander 0 (0%)
Black or African American 4 (1.8%)
White 212 (93.4%)
More than one race 4 (1.8%)
Ethnicity, n = 229
Hispanic or Latino/a/x 10 (4.3%)
Not Hispanic or Latino/a/x 219 (95.6%%)
Education Level, n = 230
Less than Bachelor’s 66 (28.7%)
Bachelor’s 78 (33.9%)
Masters 49 (21.3%)
Doctoral/Professional Degree 37 (16.1%)
Income Level, n = 230
<30,000 38 (16.5%)
30-70,000 86 (37.4%)
>70,000 106 (46.1%)
Marital Status, n = 231
Single 23 (10%)
Married/Co-Habitating 206 (89.2%)
Separated/Divorced 2 (0.9%)
Age, M(SD), n = 229 37.93 (7.20)
Study Measures M(SD)
Depressive symptoms, 4-weeks postpartum, n = 231 34.88 (9.79)
Psychological Inflexibility, 8-weeks postpartum, n = 201 14.16 (6.44)
Depressive symptoms, 12-weeks postpartum, n = 201 31.46 (7.91)
Lifetime history of depression, n (%), n = 227 63 (27.8%)
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Note. All ns are reported to reflect missingness and attrition.

Descriptive statistics include participants who completed the first self-report postpartum assessment (4-weeks postpartum), required for inclusion in this analysis.

The mediation analysis examined four pathways: 1) 4-weeks postpartum depression to 8-weeks postpartum PI; 2) 8-weeks postpartum PI to 12-weeks postpartum depression; 3) 4-weeks postpartum depression to 12-weeks postpartum depression (direct effect); and 4) 4-weeks postpartum depression to 12-weeks postpartum depression through 8-weeks postpartum PI (indirect effect). The total effect c represents the sum of the direct and indirect effects. Included as a covariate in the model was lifetime history of depression, as measured by the SCID-5, as this variable has been identified in prior work as a predictor of postpartum depression.

Results

Depressive symptoms at 4-weeks postpartum predicted psychological inflexibility at 8-weeks postpartum (β = 0.32, SE = 0.05, t(177) = 6.06, p < .001). Lifetime history of major depression was not a significant covariate the first step (p > .05). Psychological inflexibility at 8-weeks postpartum predicted depressive symptoms at 12-weeks postpartum (β = 0.32, SE = .08, t(176) = 4.09, p < .001), as did depressive symptoms at 4-weeks postpartum (β = 0.42, SE = 0.06, t(176) = 7.12, p < .001). History of depression was not a significant covariate in this step (p > .05). With 4-week depressive symptoms, 8-week psychological inflexibility, and lifetime history of depression in the model, 42% of the variance in 12-week depressive symptoms was accounted for (R2 = 0.42). The direct effect of 4-week depressive symptoms on 12-week depressive symptoms accounted for 36% of the variance in the model when controlling for history of depression. The confidence interval of the indirect effect of 4-week depressive symptoms through 8-week psychological inflexibility on 12-week depressive symptoms did not include zero (Effect = .10, Bootstrapped SE = 0.04, Bootstrapped CI = [0.04, 0.18]), indicating a significant indirect effect of psychological inflexibility. Standardized indirect effect values are included for reference (Effect = 0.11, Bootstrapped SE = 0.03, Bootstrapped CI = [0.05, 0.18]). See Figure 1 for visual depiction of the findings.

Figure 1.

Figure 1.

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Examining the mediating role of psychological inflexibility in the relation between 4-weeks and 12-weeks postpartum depression.

Note. Depressive symptoms at 4-weeks postpartum and 12-weeks postpartum were measured using the IDAS-GD. Psychological inflexibility was measured using the AAQ – II. Lifetime history of depression, as assessed with the SCID-5, was included as a covariate. n = 180. a is the path from 4-weeks postpartum depression to 8-weeks psychological inflexibility with history of depression as a covariate. b is the path from 8-weeks psychological inflexibility predicting 12-weeks postpartum depression, controlling for 4-weeks postpartum depression and history of depression. c is the total effect, including the direct and indirect effects. c’ is the direct effect.

Discussion

The present study sought to evaluate psychological inflexibility, a transdiagnostic process that the authors supposed is related to maintenance of depressive symptoms throughout the postpartum period. The objective was to identify a therapeutic process that may be utilized in future research to evaluate the effectiveness of behavioral interventions during the perinatal period. The findings determined that PI mediated the relation between 4- and 12-week postpartum depressive symptoms. The model accounted for 42% of the variance in 12-week postpartum depressive symptoms, and the direct effect accounted for the majority of the variance (36%). As such, these findings identify a relatively small effect of psychological inflexibility on depressive symptoms throughout the postpartum period among a community sample. The results are notable in that they highlight a target for future intervention and prevention work. Furthermore, work with clinical, at-risk, and diverse samples are important next steps to extend this work.

Prior work has identified PI and its key component part – experiential avoidance – as a transdiagnostic process that is targeted in Acceptance and Commitment Therapy (ACT) and several other behavioral therapies (Kashdan et al., 2006; Levin et al., 2014). The AAQ-II has also been linked to depressive symptoms in clinical (Rueda & Valls, 2016) and non-clinical samples (Levin et al., 2014). Importantly, research has also utilized the AAQ as a longitudinal predictor of mood and anxiety symptoms in multiple samples (Mellick et al., 2019; Spinhoven et al., 2014). Several aforementioned studies have examined PI and its components among perinatal samples, with indications that higher levels of PI are associated with poorer outcomes (Evans et al., 2012; Fonseca et al., 2018; Stotts et al., 2019). In summary, the results of the present investigation align well with prior research. Importantly, the extant literature utilizes primarily self-report measures of symptoms that impede diagnostic conclusions. The present study assessed lifetime history of major depression with the SCID-5 during pregnancy to characterize the sample’s history of depression, as this is known to be a robust risk factor for postpartum depression (Kroska & Stowe, 2020).

Given that the DSM-5-TR’s time specification for the perinatal period (pregnancy – 4-weeks postpartum), it is critical to identify modifiable therapeutic processes that play a role in the maintenance or alleviation of symptoms during this important period of familial development. The results suggest that PI is one such modifiable process. Psychological inflexibility mediated a positive relation between 4- and 12-weeks postpartum depressive symptoms, suggesting that those reporting more inflexibility were experiencing greater symptom maintenance across the postpartum period. The findings highlight a possible target for future intervention research. ACT is one approach that has targeted inflexibility and rigid behavioral responding through facilitating awareness of internal experiences, functional awareness, and values-based behavior. From an ACT perspective, and congruent with the literature, inflexible responses may provide short-term relief from the difficult thoughts or emotions, but in the longer term, these responses are likely to increase contact with the painful stimuli (Chawla & Ostafin, 2007). Most importantly, inflexibility reduces contact with valued life directions, resulting in fewer opportunities for positive reinforcement (S. C. Hayes et al., 2006). For example, a postpartum parent may feel shame in asking others for help with their child, and in response, not ask for help or support when needed. This functionally avoidant behavior would likely result in short-term relief from shame, but in the long-term, the parent may experience symptoms of depression and may feel disconnected from key social supports. An ACT therapist may discuss alternative responses to shame, build functional awareness of behaviors, and encourage values-based behavior. PI is a target that has the potential to impact many facets of a parent’s psychological functioning, as well as the parent’s connection with vitality and sources of meaning. Given the many physical, social, psychological, and familial changes that are occurring simultaneously for parents and families during this period, a transdiagnostic therapeutic modality is particularly important to provide optimal applicability of learned skills and to maximize efficiency during this relatively short, but critical, interval.

Future Research

The present study should be considered with several limitations in mind. First, the community sample was largely homogenous, as most participants were White, well-educated, and married or cohabitating. Biological sex was measured, not gender identity, which is a notable limitation in measurement that should be included in future research. Second, all participants were receiving at least some prenatal care, and as such, future research should examine similar constructs among more diverse samples, including pregnant people who are not receiving prenatal care. Third, the online assessments that measured PI during the postpartum period were self-report instruments, which introduces social desirability biases. Additionally, the AAQ-II has notable limitations (Ong et al., 2019; Tyndall et al., 2019), including that many of the references in this manuscript differ in terms of the specific construct the measure is purported to measure (i.e., psychological inflexibility or experiential avoidance). Though the AAQ-II is validated, clinician-administered interviews assessing PI should also be validated and used in future research so that additional context can be provided, and relations with diagnostic conclusions can be derived. Finally, the sample reported relatively low levels of symptoms across mood and anxiety disorders and throughout the perinatal period, which is congruent with expectations for a community sample.

In conclusion, the present study identified PI as a mediator of the relation between 4- and 12-weeks postpartum depressive symptoms, while controlling for lifetime history of depression. Given that the early postpartum period is a critical window for parents, children, and families, identification of key therapeutic processes is important. The present sample was a community sample of women seeking prenatal care at a large academic medical center, and future work should consider examining similar questions in clinical, at-risk, and diverse samples to further expand this area of research. Moreover, these findings emphasize the importance of PI as a possible transdiagnostic target for future intervention research. Given that ACT interventions target psychological inflexibility, this study positions ACT as an intervention that may be well-suited to women experiencing postpartum depression. Further intervention research is needed to establish the efficacy of ACT for postpartum depression and examine psychological inflexibility as a mechanism of action in treatment outcome research. As parents and families navigate early postpartum adjustment, identification of therapeutic processes that may facilitate reduction in depression is important. The findings herein suggest one such process, psychological inflexibility, and provide several directions for expansion of this important area of research.

Highlights.

  • Depression is common during the postpartum period and can have serious consequences

  • Psychological inflexibility is a transdiagnostic and modifiable therapeutic process

  • Women were recruited and completed assessments during pregnancy and postpartum

  • Psychological inflexibility mediated depression from 4- to 12-weeks postpartum

  • Psychological inflexibility may be a target for improving perinatal depression

Funding:

Study data were collected and managed using REDCap electronic data capture tools hosted at the University of Iowa. The Institute for Clinical and Translational Science provided contact information for all pregnant women at a large Midwestern hospital. The Institute for Clinical and Translational Science at the University of Iowa is supported by the National Institutes of Health (NIH) Clinical and Translational Science Award (CTSA) program, grant U54TR001356. The CTSA program is led by the NIH’s National Center for Advancing Translational Sciences (NCATS). This publication’s contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIH.

Footnotes

Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Conflicts of Interest: The authors do not have relevant conflicts of interest to disclose related to this work. Given their role as an Editorial Board Member, Emily B.K. Thomas had no involvement in the peer-review of this article and had no access to information regarding its peer-review.

Ethical Approval: This study was approved by the University of Iowa’s IRB, and all subjects provided written informed consent before taking part in study procedures.

Data Availability Statement:

Data is available upon reasonable request.

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Data Availability Statement

Data is available upon reasonable request.

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