Participants

Participants were recruited by the Bipolar Disorder Research Network (BDRN; bdrn.org) as part of a large ongoing UK study into the genetic and non-genetic causes of mood disorders. The study has UK National Health Service (NHS) Research Ethics Committee approval and local Research and Development approval in all participating NHS Trusts/Health Boards. Informed consent was obtained from each participant. Participants were recruited systematically, via community mental health teams from across the UK, and non-systematically, via local and national media coverage and via advertisements placed in local general practitioner surgeries, on the BDRN website and circulated by the national charity, Bipolar UK.

Participants are included in the BDRN research programme if they meet the following inclusion criteria: 1) aged 18 years or older; 2) able to provide voluntary written informed consent; 3) are of UK White ethnicity, due to a focus on molecular genetics and 4) meet DSM-IV [3] criteria for major affective disorder. Individuals are excluded if they: 1) have only experienced affective illness in relation to or as a result of alcohol or substance misuse; 2) have only experienced affective illness as a result of medical illness or medication; 3) have an organic neurological or other cognitive impairment, which limits their ability to complete the assessments; or 4) are biologically related to another study participant.

Parous women with a best-estimate main lifetime diagnosis of DSM-IV bipolar I disorder (BD-I, recruited between 06/2001–03/15) who had completed at least one of the questionnaires listed below were included in the current study and stratified to two groups according to their lifetime perinatal psychiatric history:

I. PP group - women who had experienced an episode of mania or psychosis within 6 weeks of delivery (n = 284). As there is currently no consensus regarding the temporal cut-off that should be used to define the postpartum period, we used a definition of 6 weeks to be consistent with our previous studies and both DSM-5 (4 weeks) and ICD-11 [52] (6 weeks) postpartum onset criteria. II. No perinatal mood episode (No PME) group – parous women without a history of mood episodes with onset during pregnancy or within 6 months following delivery (n = 268).

Psychiatric assessment

Lifetime psychopathology was assessed via interview by a trained member of BDRN (research psychologist or psychiatrist) using the Schedules for Clinical Assessment in Psychiatry (SCAN, [50]). All participants were asked about the lifetime occurrence of pregnancies and lifetime occurrence of psychiatric episodes in the perinatal period. Where available, psychiatric case notes were also reviewed. Interview and case note data were combined for each participant to make key lifetime clinical and diagnostic ratings. In cases of doubt, diagnostic and clinical ratings were made by at least two members of the research team blind to each other’s ratings and consensus was reached via discussion where necessary. Inter-rater reliability was formally assessed using 20 random cases. Mean kappa statistics were 0.85 for DSM–IV diagnosis, 0.97 for lifetime perinatal psychiatric history, and ranged between 0.81 and 0.99 for other key clinical categorical variables. Mean intra-class correlation coefficients were between 0.91 and 0.97 for key clinical continuous variables (for example, age at illness onset).

Questionnaires

Participants were asked to complete a battery of self-report questionnaires, either at the time of the initial clinical interview or subsequently as part of a questionnaire mail out.

As questionnaires were administered at different stages of the recruitment process, and completion optional, not all participants completed all questionnaires.

Six widely-used self-report questionnaires, all with demonstrated validity and reliability, were used in this study based on their measurements of personality traits, cognitive styles and affective temperaments that have previously been associated with BD.

1. Eysenck Personality Questionnaire (EPQ)

The 90-item version of the EPQ [16] was used in this study. Each item is rated ‘yes’ or ‘no’ by respondents, resulting in scores for three personality dimensions: extraversion (EPQ-E), neuroticism (EPQ-N) and psychoticism (EPQ-P). Only EPQ-E and EPQ-N were considered in this study due to their previous association with BD. Scores for EPQ-E range from 0 to 21 and EPQ-N from 0 to 23. Higher scores indicate higher levels of extraversion and neuroticism respectively.

2. Kings Schizotypy Questionnaire (KSQ)

The KSQ [29] is a 63-item questionnaire, which measures schizotypal personality traits on 7 subscales: recurrent illusions 1, social isolation, social anxiety, magical thinking, recurrent illusions 2, paranoid ideation and ideas of reference. Each item is rated ‘yes’ or ‘no’ by respondents. Total scores range from 0 to 63 and subscale scores from 0 to 9. Higher total and subscale scores indicate higher levels of schizotypy.

3. Barratt Impulsiveness Scale (BIS)

The BIS [37] is a 30-item questionnaire that measures trait impulsivity. Items are rated from 1 (absent) to 4 (most extreme). Total scores range from 30 to 120. Higher scores indicate higher levels of impulsivity.

4. Rosenberg Self-Esteem Questionnaire (SEQ)

The SEQ [41] is a 10-item questionnaire, which measures trait self-esteem. 5 questions are positively phrased and 5 questions are negatively phrased, corresponding to a positive and negative subscale respectively. Items are rated from 1 (strongly agree) to 4 (strongly disagree). Total scores range from 10 to 40, with higher scores indicating higher levels of self-esteem. Subscale scores range from 5 to 20, with high scores on the positive subscale indicating high positive self-esteem and high scores on the negative subscale indicating low negative self-esteem.

5. Dysfunctional Attitude Scale (DAS)

The DAS [40] measures underlying pervasive dysfunctional beliefs and attitudes. The 24 items are rated from 1 (totally agree) to 7 (totally disagree). Total scores range from 24 to 168. Three subscales are also scored (achievement, dependence, self-control), ranging from 0 to 56. Higher scores indicate a higher level of dysfunctional attitudes.

6. Temperament Evaluation of Memphis, Pisa, Paris and San Diego Auto-questionnaire Version (TEMPS-A)

TEMPS-A [1] is a 39-item questionnaire, which measures affective temperament on 5 subscales: cyclothymic, hyperthymic, depressive, irritable and anxious. TEMPS-A was developed specifically for use in an affectively ill population. Each item is rated ‘true’ or ‘false’ by respondents. With the exception of cyclothymic and anxious temperaments (scored from 0 to 12 and 0–3 respectively), subscale scores range from 0 to 8. Higher scores indicate higher affinity for each temperament.

Measures of current mood state

Responses to the personality, cognitive style and affective temperament questionnaires can be affected by current mood symptoms. Therefore two widely used self-report measures of current mood symptoms, the Beck Depression Inventory (BDI) and the Altman Mania Scale (AMS), were administered alongside all questionnaires.

The BDI [4] is a 21-item questionnaire measuring the severity of current depression symptoms. Total scores range from 0 to 63. Higher scores indicate greater severity of depression.

The AMS [2] is a 5-item questionnaire measuring the severity of current manic symptoms. Total scores range from 0 to 20. Higher scores indicate greater severity of mania.

Statistical analysis

Statistical analyses were carried out using the Statistical Package for the Social Sciences (SPSS) version 24.0. Categorical data (including demographic, clinical and pregnancy-related variables) were compared between the PP and No PME groups using chi-squared tests. Continuous data were not normally distributed; therefore medians, interquartile ranges and ranges are used to describe these data. Continuous data (including all questionnaire and subscale scores) were compared between the two groups using Mann-Whitney U tests. A stringent level of significance was set at 1% for the personality, cognitive style and affective temperament questionnaires to account for multiple testing.

Binary logistic regression analyses, using the enter method, were conducted to determine if any personality, cognitive style and affective temperament measures predicted group membership (PP versus No PME) controlling for potential demographic and clinical confounders (method of recruitment, age at interview, highest educational attainment and age at illness onset) and current mood state (BDI and AMS scores).