Postnatal depression (PND) is a depressive disorder for which onset is within one month after childbirth [1American Psychiatric Association. Diagnostic and statistical manual of mental disorders 5^th ed. 2013.]. Its prevalence is approximately 13% [2Beck CT. Predictors of postpartum depression: An update. Nurs Res 2001; 50(5): 275-85.
[http://dx.doi.org/10.1097/00006199-200109000-00004] [PMID: 115 70712] , 3O’hara MW, Swain AM. Rates and risk of postpartum depression—a meta-analysis. Int Rev Psychiatry 1996; 8(1): 37-54.
[http://dx.doi.org/10.3109/09540269609037816] ] worldwide and, in Japan, it is approximately 5% [4Kitamura T, Yoshida K, Okano T, et al. Multicentre prospective study of perinatal depression in Japan: Incidence and correlates of antenatal and postnatal depression. Arch Women Ment Health 2006; 9(3): 121-30.
[http://dx.doi.org/10.1007/s00737-006-0122-3] [PMID: 16547826] ]. PND is a mental health issue for both women and their children. For example, the prevalence of perinatal women who have thoughts of self-harm is 5–14%, and the prevalence of suicides as the cause of women’s death within one year after childbirth reaches 20% [5Lindahl V, Pearson JL, Colpe L. Prevalence of suicidality during pregnancy and the postpartum. Arch Women Ment Health 2005; 8(2): 77-87 .
[http://dx.doi.org/10.1007/s00737-005-0080-1] ]. PND also has negative effects on early mother-infant relationships and child development [6Moehler E, Brunner R, Wiebel A, Reck C, Resch F. Maternal depressive symptoms in the postnatal period are associated with long-term impairment of mother-child bonding. Arch Women Ment Health 2006; 9(5): 273-8.
[http://dx.doi.org/10.1007/s00737-006-0149-5] [PMID: 16937313] , 7Wan MW, Green J. The impact of maternal psychopathology on child-mother attachment. Arch Women Ment Health 2009; 12(3): 123-34.
[http://dx.doi.org/10.1007/s00737-009-0066-5] ]. The child-caring ability of mothers with PND is impaired [8Leiferman JA, Ollendick TH, Kunkel D, et al. Mothers' mental distress and parenting practices with infants and toddlers. Arch Women Ment Health 2005; 8(4): 243-47.-10Paulson JF, Dauber S, Leiferman JA. Individual and combined effects of postpartum depression in mothers and fathers on parenting behavior. Pediatrics 2006; 118(2): 659-68.
[http://dx.doi.org/10.1542/peds.2005-2948] [PMID: 16882821] ]. Thus, PND is a major health issue for families.

As a means of PND screening, many instruments have been developed [11Boyd RC, Le HN, Somberg R. Review of screening instruments for postpartum depression. Arch Women Ment Health 2005; 8(3): 141-53.
[http://dx.doi.org/10.1007/s00737-005-0096-6] [PMID: 16133785] , 12Brodey BB, Goodman SH, Baldasaro RE, et al. Development of the Perinatal Depression Inventory (PDI)-14 using item response theory: a comparison of the BDI-II, EPDS, PDI, and PHQ-9. Arch Women Ment Health 2016; 19(2): 307-16.
[http://dx.doi.org/10.1007/s00737-015-0553-9] [PMID: 26271280] ] Among them is the Edinburgh Postnatal Depression Scale (EPDS; Cox, Holden & Sagovsky, 1987) [13Cox JL, Holden JM, Sagovsky R. Detection of postnatal depression. Development of the 10-item Edinburgh Postnatal Depression Scale. Br J Psychiatry 1987; 150(6): 782-6.
[http://dx.doi.org/10.1192/bjp.150.6.782] [PMID: 3651732] ], which was translated into multiple languages and evaluated in many countries including Japan [14Okano T, Murata M, Masuji F, et al. Validation and reliability of Japanese version of the EPDS. Arch Psychiatr Diagn Clin Evaluation 1996; 74: 525-33. [in Japanese].]. Although the EPDS was developed as a screening instrument with a cut-off point to identify women who are likely to suffer from PND, it has also been used as a measure of PND severity [15Chen C, Gao J, Zhang J, Jia L, Yu T, Zheng Y. Serum leptin level measured 48 h after delivery is associated with development of postpartum depressive symptoms: A 3-month follow-up study. Arch Women Ment Health 2016; 19(6): 1001-8.
[http://dx.doi.org/10.1007/s00737-016-0647-z] [PMID: 27295066] -19Takehara K, Tachibana Y, Yoshida K, Mori R, Kakee N, Kubo T. Prevalence trends of pre- and postnatal depression in Japanese women: A population-based longitudinal study. J Affect Disord 2018; 225: 389-94.
[http://dx.doi.org/10.1016/j.jad.2017.08.008] [PMID: 28846961] ].

Similar to other types of depression, the symptomatology of PND is multifaceted. The number of factors of PND symptomatology differs from one to three in previous studies. Thus, configural invariance remains debatable. For example, a Norwegian study of the EPDS [20Berle JØ, Aarre TF, Mykletun A, Dahl AA, Holsten F. Screening for postnatal depression. Validation of the Norwegian version of the Edinburgh Postnatal Depression Scale, and assessment of risk factors for postnatal depression. J Affect Disord 2003; 76(1-3): 151-6.
[http://dx.doi.org/10.1016/S0165-0327(02)00082-4] [PMID: 12943 945] ] was reported to have a single-component structure by Principal Component Analysis (PCA) in a sample of 411 women at six to 12 weeks postpartum. The French version of the EPDS was also examined by PCA, and a two-component structure was detected in a sample of 87 women in the first four months postpartum [21Guedeney N, Fermanian J. Validation study of the French version of the Edinburgh Postnatal Depression Scale (EPDS): New results about use and psychometric properties. Eur Psychiatry 1998; 13(2): 83-9.
[http://dx.doi.org/10.1016/S0924-9338(98)80023-0] [PMID: 19698 604] ]. Tuohy et al. [22Tuohy A, McVey C. Subscales measuring symptoms of non-specific depression, anhedonia, and anxiety in the Edinburgh Postnatal Depression Scale. Br J Clin Psychol 2008; 47(Pt 2): 153-69.
[http://dx.doi.org/10.1111/j.2044-8260.2008.tb00463.x] [PMID: 177 61026] ], in a PCA study, reported that the English version of the EPDS had a three-component structure including anhedonia, anxiety, and depression. Similarly, the Vietnamese, Turkish, and Filipino versions of the scale by PCA at six to nine months postpartum were examined and it was reported that these versions of the EPDS had a three-component structure [23Small R, Lumley J, Yelland J, Brown S. The performance of the Edinburgh Postnatal Depression Scale in English speaking and non-English speaking populations in Australia. Soc Psychiatry Psychiatr Epidemiol 2007; 42(1): 70-8.
[http://dx.doi.org/10.1007/s00127-006-0134-3] [PMID: 17102922] ]. Previously, PCAs and EFAs that were statistically different [24Yong AG, Pearce S. A beginner’s guide to factor analysis: Focusing on exploratory factor analysis. Tutor Quant Methods Psychol 2013; 9(2): 79-94.
[http://dx.doi.org/10.20982/tqmp.09.2.p079] ] were not distinguished and were treated as if they were interchangeable [25Ross LE, Gilbert Evans SE, Sellers EM, Romach MK. Measurement issues in postpartum depression part 1: Anxiety as a feature of postpartum depression. Arch Women Ment Health 2003; 6(1): 51-7.]. EFAs are preferable to PCAs because PCAs are the only data reduction method without regard to any underlying structure caused by latent variables [26Costello AB, Osborne JW. Best practices in explanatory factor analysis: Four recommendations for getting the most from your analysis. Pract Assess, Res Eval 2005; 10(7): 1-9.]. The component calculation is based on using all the variance of the indicators. This is in contrast to the idea of EFAs where researchers analyse data with a Priori theory of internal structures.

Many studies reported that the EPDS had a three-factor structure. Kubota et al. [27Kubota C, Okada T, Aleksic B, et al. Factor structure of the Japanese version of the Edinburgh Postnatal Depression Scale in the postpartum period. PLoS One 2014; 9(8)e103941
[http://dx.doi.org/10.1371/journal.pone.0103941] [PMID: 25089523] ], in a sample of 690 women at one-month postpartum, used the Japanese version of the EPDS where three factors emerged: anhedonia, anxiety, and depression. Takehara et al. [19Takehara K, Tachibana Y, Yoshida K, Mori R, Kakee N, Kubo T. Prevalence trends of pre- and postnatal depression in Japanese women: A population-based longitudinal study. J Affect Disord 2018; 225: 389-94.
[http://dx.doi.org/10.1016/j.jad.2017.08.008] [PMID: 28846961] ] re-examined the three-factor structure of the Japanese version of the EPDS reported by Kubota et al. [27Kubota C, Okada T, Aleksic B, et al. Factor structure of the Japanese version of the Edinburgh Postnatal Depression Scale in the postpartum period. PLoS One 2014; 9(8)e103941
[http://dx.doi.org/10.1371/journal.pone.0103941] [PMID: 25089523] ]. This was a six-time-point study from pregnancy to postpartum in a sample of 1,311 women in Japan. The same three-factor structure was confirmed.

A drawback of EFAs is the choice of the number of factors that are subjectively defined by the researchers. This results in different models of the factor structure. To identify the best factor structure of the EPDS, Confirmatory Factor Analysis (CFA) is necessary.

The model fit of the past investigations of the EPDS CFA studies is presented in Table 1. The Comparative Fit Index (CFI) ranged from 0.93 to 0.999 and was less than 0.97 approximately half the time. The Root Mean Square Error of Approximation (RMSEA) ranged from 0.00 to 0.10 and it was greater than 0.05 approximately 60% of the time. Therefore, the fit of the factor structure model of the EPDS among the past studies was only modest.

Table 1
The EPDS CFA studies.

This may mean that a simple first-order one-factor model of the EPDS factor structure did not necessarily represent the real picture of the item structure. Little has been argued regarding whether a higher order (or hierarchical) structure of PND exists. For example, in addition to subscales of PND including anhedonia, anxiety, and depression, we may expect a general factor of PND severity. This echoes the general factor of intelligence [28Brunner M, Nagy G, Wilhelm O. A tutorial on hierarchically structured constructs. J Pers 2012; 80(4): 796-846.
[http://dx.doi.org/10.1111/j.1467-6494.2011.00749.x] [PMID: 2209 1867] ].

In EFAs, the number of factors ranges between one and the number of items of the instrument. Thus, in the EPDS that consisted of 10 items, the number of factors in EFAs could range between one and 10. We compare in CFAs different factor structure models derived from EFAs. A single-factor model is the most parsimonious model (Fig. 1). This model predicts that individual differences in all the EPDS items are caused by individual differences in only one common latent factor. The influence of this general factor is represented by a factor loading that is depicted in the figure as a single-headed arrow. A single factor model has the greatest number of df. When the single-factor model does not fit the data satisfactorily, we should consider a first-order factor model with more than one latent factor; for example, a two-factor model. In this model, each EPDS item is considered to be influenced by one of the first-order factors (Figs. 2 and 3). In a two-factor model of the EPDS, for example, items 1 and 2 are influenced only by the second factor, whereas the other eight items are influenced only by the first factor. The first-order factors are considered to be correlated with each other. If all the factor correlations in a first-factor model are fixed to r =1.0, it is equivalent to the single-factor model. Therefore, the former nests the latter. The df of a first-order factor model is lower than that of a single-factor model. If χ² decreases significantly for the df difference, we adopt the first-order model,whereas if χ² does not decrease significantly for the df difference between the two models, we retain the single-factor model as the best model for the sake of parsimony. This procedure will be continued to a model with a greater number of factors until the χ² difference does not reach the significance level.

The difference between single- and first-order factor models lies in the fact that the former focuses on general abilities (e.g., severity of depression), whereas the latter focuses on several specific abilities (e.g., anhedonia, anxiety, and dysphoria among depression symptoms). We consider that the general and specific abilities are located at different levels of the ability hierarchy. Neither model addresses both general and specific abilities simultaneously. When, as is the case of many psychological measurements, the models of a single- or first-factor structure do not satisfactorily fit the data, it is plausible to consider higher-order factor and bifactor models. These models take into account the general and specific abilities in their entirety [28Brunner M, Nagy G, Wilhelm O. A tutorial on hierarchically structured constructs. J Pers 2012; 80(4): 796-846.
[http://dx.doi.org/10.1111/j.1467-6494.2011.00749.x] [PMID: 2209 1867] ]. In a higher-order factor model (also known as a second-order model or an indirect hierarchical model), as in the single- or first-order factor models, each indicator is influenced by one of the first-order factors. In addition, each first-order factor is influenced by the general factor (Fig. 4). The shared variance of the higher-order factors is accounted for by the second-order general factor, which is unlikely with the first-order factor models. In other words, the first-order factor model assumes that factors are correlated and that the construct (e.g., postnatal depression) is multidimensional and explained by obliquely related dimensions. In contrast, the second-order model assumes that the factors are uncorrelated and represented by a general depression construct. Therefore, the general factor influences each indicator indirectly via first-order factors.

Fig. (1) Single-factor model of the EPDS items. CFI, Comparative Fit Index; RMSEA, Root Mean Square Error of Approximation; AIC, Akaike Information Criteria. Paths are standardised. The Names of Error Variables are Deleted.

Fig. (2) Two-factor model of the EPDS items. CFI, Comparative Fit Index; RMSEA, Root Mean Square Error of Approximation; AIC, Akaike Information Criteria. Paths are standardised. The names of error variables are deleted.

Fig. (3) Three-factor model of the EPDS items. CFI, Comparative Fit Index; RMSEA, Root Mean Square Error of Approximation; AIC, Akaike Information Criteria. Paths are standardised. The names of error variables are deleted.

Fig. (4) Second-order factor model of the EPDS items. CFI, Comparative Fit Index; RMSEA, Root Mean Square Error of Approximation; AIC, Akaike Information Criteria. Paths are standardised. The names of error variables are deleted.

In the bifactor model (also known as a hierarchical factor model or an indirect hierarchical factor model), the general factor influences all the indicators directly but not via the first-order factors (Fig. 5). The idea is that all the indicators differ according to the general factor, whereas groups of indicators are dependent on each first-factor they belong to independently from the influence of the general factor. Here, the general factor and the first-order factors are independent of each other. For example, an indicator (e.g., “cannot see the funny side of things” is a reflection of a specific aspect (e.g., anhedonia) as well as the general severity (of depression). In our study, we compared different models of EPDS factor structures. We also compared our models with that proposed by Kubota et al. [27Kubota C, Okada T, Aleksic B, et al. Factor structure of the Japanese version of the Edinburgh Postnatal Depression Scale in the postpartum period. PLoS One 2014; 9(8)e103941
[http://dx.doi.org/10.1371/journal.pone.0103941] [PMID: 25089523] ].

The above argument implies not only statistical precision but also causal as well as consequential issues. For example, even though scores of a subscale were correlated with a possible predictor, it may be a spurious product confounded by the general factor. Such a hypothesis can be examined by Structural Equation Modelling (SEM) where the external variable (a predictor) sends paths to the subscale factors and the general factor (Fig. 6). Also, the case is the influence of specific and general factors on outcome variables (e.g., parenting difficulties in the case of PND). Our study tries to explore different associations of the factor structure we identify as the best fit with the data with demographic, obstetric, and psychosocial variables. We consider that such results may contribute to the construct validity of the model statistically identified [29Messick S. Validity of psychological assessment: Validation of inferences from persons’ responses and performances as scientific inquiry into score meaning. Am Psychol 1995; 50(9): 741-9.
[http://dx.doi.org/10.1037/0003-066X.50.9.741] ].

Fig. (5) Bifactor model of the EPDS items. CFI, comparative fit index; RMSEA, root mean square error of approximation; AIC, Akaike information criteria. Paths are standardised. Significant paths are in bold. The names of error variables are deleted. Paths with significant (p< .05) coefficients are in bold.

Fig. (6) Predictors and the EPDS general and subscale scores. The names of error variables are deleted.

In this study, we selected variables related to Negative Life Events (NLEs) occurring after childbirth and coping styles and behaviours as external indicators. The postnatal period may be characterised as a life stage with many stressors. This period sees a dynamic role transition related to the parental role, adaptation to physical changes, and altered relationships with the spouse, other children, co-workers, or significant others [30Condon JT, Boyce P, Corkindale CJ. The First-Time Fathers Study: A prospective study of the mental health and wellbeing of men during the transition to parenthood. Aust N Z J Psychiatry 2004; 38(1-2): 56-64.
[http://dx.doi.org/10.1177/000486740403800102] [PMID: 14731195] -38Simpson JA, Rholes WS, Campbell L, Tran S, Wilson CL. Adult attachment, the transition to parenthood, and depressive symptoms. J Pers Soc Psychol 2003; 84(6): 1172-87.]. Mothers of infants must adapt to the physical and social changes brought about by pregnancy, adopt their new role as a mother, and build new relationships. Hence, they are likely to experience emotional conflicts in themselves and social problems with others. Maternal identity should be established and mothers must learn new social skills to cooperate with others as well as to build a new family. Interpersonal conflict may manifest after childbirth. This may be related to childcare responsibilities and managing the newborn. This, coupled with a poor marital relationship, may lead to psychological maladjustment. Mothers may also have feelings of isolation because they have less time to communicate with other adults compared during non-childbearing periods. Thus, the postpartum period is stressful for women because of the increased incidence of these NLEs. This study explores specific associations that different aspects of PND symptomatology have with different types of NLEs.

Coping is the perception or behaviours people have or take when expecting or facing NLEs [39Lazarus RS, Folkman S. Stress, appraisal, and coping 1984., 40Snyder CR, Ford CE, Eds. Coping with negative life events: Clinical and social psychological perspectives 1987.
[http://dx.doi.org/10.1007/978-1-4757-9865-4] ]. The concept of coping has two components [41Beutler LE, Moos RH, Lane G. Coping, treatment planning, and treatment outcome: discussion. J Clin Psychol 2003; 59(10): 1151-67.
[http://dx.doi.org/10.1002/jclp.10216] [PMID: 12968279] , 42Moos RH, Holahan CJ. Dispositional and contextual perspectives on coping: toward an integrative framework. J Clin Psychol 2003; 59(12): 1387-403.
[http://dx.doi.org/10.1002/jclp.10229] [PMID: 14618606] ]. One is a stable coping style or styles that characterise an individual’s reactions to stressful situations. Another is a set of skills or techniques (coping behaviours) that people use to manage specific stressful situations. The former is dispositional and is part of ones personality [43O'Brien TB, DeLongis A. The interactional context of problem-, emotion-, and relationship-focused coping: The role of the big five personality factors. J Pers 1996; 64(4): 775-813., 44Vollrath M, Torgersen S, Alnæs R. Personality as long-term predictor of coping. Pers Individ Dif 1995; 18(1): 117-25.
[http://dx.doi.org/10.1016/0191-8869(94)00110-E] ]. In contrast, the coping behaviours may be determined more by one’s current situation [45McCrae RR. Situational determinants of coping responses: Loss, threat, and challenge. J Pers Soc Psychol 1984; 46(4): 919-28.
[http://dx.doi.org/10.1037/0022-3514.46.4.919] [PMID: 6737200] ]. The choice of coping behaviours is determined by the specificity of a situation. The coping styles and coping behaviours are moderately correlated [46Shikai N, Nagata T, Kitamura T. Do people cope with situations as they say? Relationship between perceived coping style and actual coping response. Psychiatry Clin Neurosci 2014; 68(2): 154-9.
[http://dx.doi.org/10.1111/pcn.12094] [PMID: 24118236] ]. This study explores specific associations that different aspects of PND symptomatology have with different aspects of coping characteristics.

These methodological considerations based on the recent development of statistics related to factor structure prompted us to reanalyse the data we collected in the previous studies conducted several years ago.

The present study showed that among the three-factor structure models of the full EPDS―the single-, two-, and three-factor models―the three-factor model showed the best fit with the model. However, the three-factor model of Kubota et al. (2014) [27Kubota C, Okada T, Aleksic B, et al. Factor structure of the Japanese version of the Edinburgh Postnatal Depression Scale in the postpartum period. PLoS One 2014; 9(8)e103941
[http://dx.doi.org/10.1371/journal.pone.0103941] [PMID: 25089523] ], which excluded items 6 ‘things have been getting on top of me’ and 10 ‘thought of harming myself’ fit better than ours. Item 6 showed a factor loading >0.3 in none of the three models in our study. This is in accordance with previous studies [22Tuohy A, McVey C. Subscales measuring symptoms of non-specific depression, anhedonia, and anxiety in the Edinburgh Postnatal Depression Scale. Br J Clin Psychol 2008; 47(Pt 2): 153-69.
[http://dx.doi.org/10.1111/j.2044-8260.2008.tb00463.x] [PMID: 177 61026] , 27Kubota C, Okada T, Aleksic B, et al. Factor structure of the Japanese version of the Edinburgh Postnatal Depression Scale in the postpartum period. PLoS One 2014; 9(8)e103941
[http://dx.doi.org/10.1371/journal.pone.0103941] [PMID: 25089523] , 60Cunningham NK, Brown PM, Page AC. Does the Edinburgh Postnatal Depression Scale measure the same constructs across time? Arch Women Ment Health 2015; 18(6): 793-804.
[http://dx.doi.org/10.1007/s00737-014-0485-9] [PMID: 25510935] ]. These results suggest that item 6 is unstable as an indicator of the EPDS. Item 10 showed a factor loading > 0.3, but it was skewed (> 3.0). Despite its clinical relevance (suicidality), its psychometric value may cast doubt on its use as a screening instrument or indicator of PND severity.

Another unique factor of our study is the application of the bifactor model. This resulted in an extremely better fit of the model with the data. Reichenheim et al. [61Reichenheim ME, Moraes CL, Oliveira AS, Lobato G. Revisiting the dimensional structure of the Edinburgh Postnatal Depression Scale (EPDS): Empirical evidence for a general factor. BMC Med Res Methodol 2011; 11: 93.
[http://dx.doi.org/10.1186/1471-2288-11-93] [PMID: 21689442] ] proposed bifactor modes of EPDS using 10 items and suggested that using all EPDS items is suited to clinical practices. However, our model, which consists of eight items, showed better fit indices than the three-factor model with all 10 items. A scale that consists of fewer items is usually more useful for clinicians. Therefore, we recommend using the eight-item version. This model comprised a single general dimension alongside three distinct subfactors (anhedonia, anxiety, and dysphoria). The structural conceptualisation of PND in terms of a bifactor model should help us understand the interplay between the general condition and dimensions of symptoms of PND.

Scrutiny of the factor loadings of this bifactor model indicates characteristics of PND symptomatology (Fig. 5). Although items 7, 8, and 9 were indicators of the dysphoria factor, their factor loadings were not significant. Items 7 and 9 were loaded on the general depression factor significantly. These findings may mean that these three items reflect the severity of PND, in general, more than the specific aspect of dysphoria. In contrast, items 3, 4, and 5 were loaded significantly on the anxiety factor but not significantly on the general depression factor. Hence, they may be more specific indicators, as are items 1 and 2, which were indicators of anhedonia. However, item 2 was significantly loaded on the general depression factor.

As we expected, a single general dimension alongside three distinct subfactors (anhedonia, anxiety, and dysphoria) was predicted by different predictor variables. We identified five variables as predictors: Interpersonal Relationships and Out-of-Home Activities, Parenting and Newborn Behaviours, Enacted Problem Solving, Enacted Denial, and Enacted Turning to Others. As reported previously [48Ohashi Y, Takegata M, Haruna M, Kitamura T, Takauma F, Tada K. Association of specific negative life events with depression severity one month after childbirth in community-dwelling mothers. Int J Nurs Health Sci 2015; 2(2): 13-20.], among the four predictors related to NLEs, two were identified: (a) Interpersonal Relationships and Out-of-Home Activities;and (b) Parenting and Neonatal Behaviours. Two other NLEs-Physical Symptoms and Body Image, and Lifestyle Changes and Financial Problems-showed no association with the EPDS subscale and general scores. Therefore, PND symptomatology has a specificity of the life event type. Furthermore, the variable Interpersonal Relationships and Out-of-Home Activities was associated with anhedonia and dysphoria, whereas Parenting and Neonatal Behaviours was associated with the general severity of PND. The inverse relationship between Parenting and Neonatal Behaviours and dysphoria is difficult to interpret (Fig. 10). Excessive crying and feeding problems and infants’ sleeping problems were associated with mothers’ depression and anxiety [62Nolvi S, Karlsson L, Bridgett DJ, Pajulo M, Tolvanen M, Karlsson H. Maternal postnatal psychiatric symptoms and infant temperament affect early mother-infant bonding. Infant Behav Dev 2016; 43: 13-23.
[http://dx.doi.org/10.1016/j.infbeh.2016.03.003] [PMID: 27054496] -64Tikotzky L. Postpartum maternal sleep, maternal depressive symptoms and self-perceived mother-infant emotional relationship. Behav Sleep Med 2016; 14(1): 5-22.
[http://dx.doi.org/10.1080/15402002.2014.940111] [PMID: 25127316] ]. Our results suggest that such an association is through the increased PND severity rather than direct effects on the subscale dysphoria. It may be that difficulties associated with childrearing lead to more severe PND in general and when this is controlled, focusing on childcare may prevent women from paying attention to their own mood states [65Nolen-Hoeksema S. The role of rumination in depressive disorders and mixed anxiety/depressive symptoms. J Abnorm Psychol 2000; 109(3): 504-11.
[http://dx.doi.org/10.1037/0021-843X.109.3.504] [PMID: 11016119] -68Nolen-Hoeksema S, Parker LE, Larson J. Ruminative coping with depressed mood following loss. J Pers Soc Psychol 1994; 67(1): 92-104.
[http://dx.doi.org/10.1037/0022-3514.67.1.92] [PMID: 8046585] ].

The effects of age and parity on the EPDS subscale and general scores were mediated by these NLEs. First-time mothers were more likely to experience interpersonal problems, whereas mothers with more than one child were more likely to experience childrearing difficulties. The role transition from being a marital partner only to having a dual role as a wife and mother may be more stressful for first-time mothers, whereas rearing more than one baby simultaneously may be more stressful for mothers with multiple babies.

Enacted coping behaviours were differentially associated with the general and subscale scores of the EPDS. Thus, the general depression factor was more severe when the participants used denial and problem solving more frequently, whereas anhedonia was more severe when the participants used problem-solving less frequently. Anxiety was more severe when the participants used Turning to Others more frequently. The association between PND severity and denial as the coping behaviour may be due to the widely held notion that denial is a maladaptive coping strategy [69Terry DJ, Mayocchi L, Hynes GJ. Depressive symptomatology in new mothers: A stress and coping perspective. J Abnorm Psychol 1996; 105(2): 220-31.
[http://dx.doi.org/10.1037/0021-843X.105.2.220] [PMID: 8723003] ]. Of interest is the negative association between problem-solving and PND severity. This coping pattern is usually regarded as adaptive in many studies [50Folkman S, Lazarus RS. If it changes it must be a process: Study of emotion and coping during three stages of a college examination. J Pers Soc Psychol 1985; 48(1): 150-70.
[http://dx.doi.org/10.1037/0022-3514.48.1.150] [PMID: 2980281] , 70Endler NS, Parker JD. Multidimensional assessment of coping: A critical evaluation. J Pers Soc Psychol 1990; 58(5): 844-54.
[http://dx.doi.org/10.1037/0022-3514.58.5.844] [PMID: 2348372] ]. People using problem-solving to cope in difficult situations carefully consider the causes of the difficulty and try to solve it by themselves. However, the NLEs experienced during the postnatal period are unique and often difficult to solve singlehandedly such as a baby’s cry in the night. In such a situation, the best coping strategy may be to ask for help from others. Thus, Turning to Others did not predict PND severity but, in our study, was associated with anxiety. Such behaviours may induce anxious moods, or, alternatively, anxious mothers may be likely to ask for help from others (e.g., their partner). Parity was also associated with coping behaviours. Thus, experienced mothers are likely to solve problems by themselves as well as ask for help from others.

We should discuss the clinical implications of our study. Our report suggests that parenting education and support in coping behaviours would be recommended as an intervention for PND. This is because of the severity of depression, in general, was significantly predicted by Parenting and Newborn Behaviours, Enacted Denial, and Enacted Problem Solving. Careful observation of a mother’s perceived difficulty with child care may encourage clinicians to provide child care assistance (e.g., support from family members and relatives, and NPOs such as Home Start). It has been reported that a doula’s emotional support enhances positive parenting and parent-child interactions [71Scott KD, Klaus PH, Klaus MH. The obstetrical and postpartum benefits of continuous support during childbirth. J Womens Health Gend Based Med 1999; 8(10): 1257-64.
[http://dx.doi.org/10.1089/jwh.1.1999.8.1257] [PMID: 10643833] , 72Thomas MP, Ammann G, Brazier E, Noyes P, Maybank A. Doula services within a healthy start program: Increasing access for an underserved population. Matern Child Health J 2017; 21(Suppl. 1): 59-64.
[http://dx.doi.org/10.1007/s10995-017-2402-0] [PMID: 29198051] ]. Continuous community-based support from the pregnancy to postnatal periods (e.g., home visiting) by doulas would be helpful. Neither denial nor problem solving should be recommended, but mothers should be advised to ask for support from others. Mothers may hesitate to ask for help from others. Nevertheless, excessive support seeking may be linked to anxiety. Anxious mothers who seek help from others excessively may be consulted in anxiety reduction. Difficulties with interpersonal relationships are another important clinical observation among first-time mothers in particular. Approaching these difficulties with interpersonal psychotherapy may be used as a means of intervention or prevention. Such ‘custom-made’ care and intervention may help mothers avoid PND.

Regarding the limitations of the present study, we should be cautious because this was based on only two observation points. Confounders of the results may be found in variables during the pregnancy period. Research should be extended to the whole perinatal period. NLEs after childbirth were rated by mothers themselves one month after birth simultaneously with the EPDS. The occurrence of NLEs may be a result of depression or anxiety [73Hammen C. Stress generation in depression: Reflections on origins, research, and future directions. J Clin Psychol 2006; 62(9): 1065-82.
[http://dx.doi.org/10.1002/jclp.20293] [PMID: 16810666] -75Wichers M, Maes HH, Jacobs N, Derom C, Thiery E, Kendler KS. Disentangling the causal inter-relationship between negative life events and depressive symptoms in women: A longitudinal twin study. Psychol Med 2012; 42(9): 1801-14.
[http://dx.doi.org/10.1017/S003329171100300X] [PMID: 22273464] ]. Mothers with anxiety or depression may perceive events as more stressful than other mothers. Neonatal behaviours should be rated independently by researchers, such as observation of a mother’s neonatal temperament. We were unable to make clinical diagnoses of mood and anxiety disorders. Detection of clinical cases may yield different findings. It was desirable to conduct a diagnostic interview with the mothers. Another point which needs further research is the scale’s cultural context. Obviously, we identified the factor structure of the EPDS only in Japanese culture (and language). We believe that the subscales we identified capture the different aspects of postnatal depression symptomatology. This should be compared with reports from the other cultures using different languages in the same framework of the factor structure.

Despite these drawbacks, our study expanded on a previous factor structural study of the EPDS and developed the multidimensional model. Also, this study explored different associations of the factor structure with psychological variables contributing to the construct validity of the model. The present results confirmed the presence of a general factor alongside anhedonia, anxiety, and dysphoria, presumably reflecting different aspects of the PND symptoms. Perinatal health care professionals should be encouraged to use the three subscales and the total EPDS score.