Table 1 Outcome measures: description and validity of measures as well as time points of their administration

 Maternal sensitivity

Emotional Availability Scales (EA). Observation of behaviours. Score 6 dimensions on a 1 to 7 scale. Validated for international use [79]

Year 1 and year 2

 Child attachment security

Attachment Q-Set (Q-Set). Observation of behaviours. Score on a continuum of secure to insecure. Good convergent and discriminate validity [40]

Year 2

 Child cognitive and language development

Bayley Scales of Infant and Toddler Development Scales, third edition (Bayley-III). Individual administration. Continuous scales produce scores. Validated for UK and Ireland use [43]

Year 2

 Behavioural problems

Child Behaviour Checklist (CBCL).100-item questionnaire. Responses are on a scale of 0 to 2. Validated for international use [45]

Year 2

 Postponed child-bearing

Mother asked about her pregnancy status. Number of months from baseline to the next pregnancy used for analyses. Extensive use with similar studies (e.g. [1])

6 months, year 1, 18 months and year 2

 Maternal mental health

Edinburgh Postnatal Depression (EPDS).10-item questionnaire. Responses are on a scale of 0 to 3. Validated measure of depression [47]

Baseline, year 1 and year 2

 Child quality of life (QoL)

Warwick Child Health and Morbidity Profile (WCHMP). 10-items survey. An incremental cost-effectiveness ratio (ICER) calculated. Validated with low interobserver variation [49]

Year 1 and year 2

 Health and social care resource use

Service Use and Support (SUS). 36-item questionnaire. Cost of services calculated with the Personal Social Services Research Unit (PSSRU). Extensive use in clinical studies (e.g. [80])

Baseline, 6 months, year 1, 18 months and year 2

 Measurement of temperament

Infant Behaviour Questionnaire Revised (IBQ-R). 37-item questionnaire. Responses are on a scale of 1 to 7. Good internal consistency reliability and convergent validity [52]

Year 1

 Sensitivity scale

Maternal and paternal Sense of Mastery (MSM). 7-item questionnaire. Responses are on a 7-item scale (agreement to disagreement). Extensive use with similar sample of young women [53]

Baseline, year 1 and year 2

 Social support

Norbeck Social Support questionnaire (NSSQ). 9-item questionnaire. Responses are on a scale of 0 to 4. Validity and reliability on all measures [57]

Baseline, year 1 and year 2

 Infant health outcome

Health records reviewed at the end of the study and data collected on different issues, including hospitalisation and Social Services’ referrals. Extensive use with similar studies (e.g. [1])

Year 1 and year 2

 Parental representation of their child

Parent Development Interview – Revised (PDI). 20-item interview. Scores are on a scale of 1 to 9. Validity shows links to adult attachment and child attachment [29, 32, 58, 59]

Year 1

 Stress within the parenting role

Parental Stress Inventory Short Form (PSI-SF). 36-item questionnaire. Responses are on a 5-point scale (agreement to disagreement). Short Forms show concurrent validity with the full-length PSI [62]

Year 1 and year 2

 PTSD Checklist Civilian

Posttraumatic stress disorder (PCL-5). 20-item questionnaire Responses are on a scale of 0 to 4. PCL-5 has good psychometric properties [64]

Baseline, year 1 and year 2

 State and trait anxiety

State-Trait Anxiety Inventory (STAI). 40-item questionnaire. Responses are on a scale of 0 to 4. Strong construct and concurrent validity [65, 66]

Baseline, year 1 and year 2

 Adult quality of life (QoL)

EuroQol EQ-5D 3 level (EQ-5D-3 L) 6-item questionnaire. Responses are on a scale of 0 to 2. Extensive use for similar study (e.g. [81, 82])

Baseline, year 1 and year 2

 Treatment experience

Treatment Experience Questionnaire (TEQ). 15-item questionnaire. Responses are on a 5-point scale. Based on questionnaires used in similar studies [68]

Year 1 and year 2