The present study used data from the Norwegian Mother, Father and Child Cohort Study (MoBa), conducted by the Norwegian Institute of Public Health from 1999 through 2008 (28). All pregnant women in Norway were eligible to participate in MoBa if they were able to read Norwegian. The MoBa cohort included 114,500 children and 95,200 mothers yielding a response rate of around 41% (28). Written informed consent was obtained from all MoBa participants upon recruitment and participants did not receive any financial compensation. The establishment of MoBa and the initial data collection were based on a licence from the Norwegian Data Protection Agency and approval from the Regional Committees for Medical and Health Research Ethics. The MoBa cohort is now based on regulations related to the Norwegian Health Registry Act. The current study was approved by the Regional Committees for Medical and Health Research Ethics (project no; 2017/2199) and is based on version 10 of the MoBa data files. The sample in the present study constitutes 86,724 mothers and children. Due to possible bias, twins (n = 1,480) and triplets (n = 14) were excluded.
Overall quality of life
Quality of life was measured using the Satisfaction With Life Scale (SWLS) (8) six months postpartum. The SWLS includes five items, such as ‘The conditions of my life are excellent’ and ‘I am satisfied with my life’, rated on a Likert scale ranging from 1 = Strongly Disagree, to 7 = Strongly Agree. Mean scores of the five items were computed. The scale revealed a satisfactory internal consistency, with α value 0.89. Several studies have confirmed the validity of (8, 29).
Information on child gender, gestation age and maternal age, maternal educational level, marital status, work status and experience of birth was collected from the MoBa study at 16–20 weeks of pregnancy and six months postpartum.
The Edinburgh Postnatal Depression Scale (EPDS)
Mothers’ mental health was assessed using the Edinburgh Postnatal Depression Scale (EPDS). The EPDS has a sensitivity of 86% and a specificity of 78% (30). Items are scored on a Likert scale ranging from 0 (‘no, never’) to 3 (‘yes, almost all the time’). A 6-item version was used in the MoBa study. The maximum score is 18, with high scores indicating higher levels of postnatal depression. The internal consistency: Cronbachs α was 0.84 (28).
The Differential Emotional Scale (DES)
The Differential Emotional Scale (31) consists of a series of subscales that capture various emotions. In the present study, items were selected from the Enjoyment and Anger subscales (DES-IV), and included 3 items of Joy and 3 items of Anger. The respondents rated how often they felt the different emotions on a scale from 1 to 5 where 1 = seldom/never, and 5 = very often. Mean scores were computed. The DES has been widely used in research on self-rated affect and has shown good psychometric properties (31, 32).
Feelings related to childbirth
Feelings related to childbirth were assessed six months postpartum based on the single statement ‘I felt safe and in good hands’, with the following response options; applies well, applies partly, does not apply.
Sleep duration at six months was assessed using the question, ‘How many hours does your child sleep per day’. Response categories were 10 hours or less, 11 to 12 hours, 13 to 14 hours, and 15 hours or more. We defined that the normal sleep of a child aged around six months was 13 hours or more a day.
Colic was measured at 6 months using one question in the questionnaire, ‘Has your child had the following illness/health problem? Infant colic?’ The response categories were yes or no. Parents thus answered yes if they thought their child had had colic, and no other diagnostic criteria were needed.
Child temperament was measured at six months using the Infant Characteristics Questionnaire (ICQ) (33). The original ICQ consists of 24 items describing infant behaviour. Four subscales have been identified; Fussy/Difficult, Unadaptable, Dull and Unpredictable, with varying internal consistency previously reported (.79, .75, .39, .50) (Bates et al 1979). The scale used in MoBa is the Fussy/Difficult scale (8 items). Mothers rank each item on a 7-point Likert scale (1–7), indicating the level of perceived difficulty of handling the described behaviour. Responses to negatively framed questions on the Fussy/Difficult scale were reversed, so that lower scores reflect more difficulty. The total score ranged from 7 to 49 and the internal consistency was 0.69.
Satisfaction with relationship
Satisfaction with relationship was measured using the Relationship Satisfaction Scale (RS) (34). RS is a 10-item scale developed for the MoBa study based on previously developed scales. The scale is validated, and showed good psychometric properties (34). The RS refers to a ‘partner’ instead of being limited to marital spouses, and includes the items ‘I am satisfied with the relationship with my partner’, ‘My partner and I have problems in our relationship’, ‘I am very happy in my relationship’, ‘My partner is generally understanding’, and ‘We agree on how children should be brought up’. Responses were rated on a 6-point Likert scale ranging from 1 = Strongly Disagree to 6 = Strongly Agree. Negative responses were reversed, and items added to form a sum score with a maximum score of 60.