Table 1 Overview of variables and the survey questions they originate from, adapted from [4]

Outcome – Infant feeding related measures

Duration of any breastfeeding

Did you ever breastfeed your youngest child(ren) (including expressing)? Yes, No, Prefer not to say

Are you currently providing any breastmilk to your youngest child(ren), either exclusively or alongside formula and/or solids? Yes, No

Approximately, how long did you provide any breastmilk your youngest child(ren)? Specify number and select unit (days, weeks, months)

Maternal subjective experience

How would you describe your overall experience around feeding your youngest child(ren)? Please tick all that apply. Option list included: ‘enjoyable’ and ‘rewarding’, ‘good for bonding’, ‘hard work’, ‘stressful’, ‘emotionally draining’, ‘none of the above’, and ‘prefer not to say’

Exposure – Health visitor social support measures

Informational support

Thinking back to the first few weeks after giving birth to your youngest child(ren)… on a scale of 1 to 5 with 1 being "very helpful" and 5 being "very unhelpful," how helpful did you find the health visitors advice and/or information overall? ‘very helpful’, ‘helpful’, ‘neither helpful nor unhelpful’, ‘unhelpful’, ‘very unhelpful’, ‘not applicable’

Emotional support

Thinking back to the first few weeks after giving birth to your youngest child(ren)…how emotionally supported did you feel by your health visitor? ‘very supported’, ‘supported’, ‘neither supported nor unsupported’, ‘unsupported’, ‘very unsupported’, ‘not applicable’

Controls

Age of mother

In what year were you born (yyyy)

Educational attainment

What is your highest qualification level? GCSEs or equivalent, AS/A-levels or equivalent, Graduate or equivalent, Postgraduate or equivalent, Other

Intention to breastfeed

I planned to breastfeed my baby(ies). Yes, no

Breastfeeding exposure

Thinking back to before you gave birth to your youngest child(ren), what were your thoughts and experiences around feeding your baby(ies)? Please select all that apply… ‘I knew people who were breastfeeding / had breastfed their baby(ies)’

Mother breastfed

Were you breastfed as a baby? ‘Yes’, ‘no’, ‘don’t know’

Parity

In total, how many children do you have?

Annual income

Approximately, what is your total annual household income? ‘Less than £10,000’, ‘Between £10,000 and £20,000’,’ Between £20,000 and £30,000’, ‘Between £30,000 and £40,000’, ‘Between £40,000 and £50,000’,’ Between £50,000 and £60,000’, ‘Between £60,000 and £70,000’, ‘Between £70,000 and £80,000’, ‘£80,000 or more’, ‘don’t know’, ‘Prefer not to say’