Table 1 Primary and secondary outcome variables and measurement
Variable | Measurement | Source | Assessment timing |
|---|---|---|---|
Primary Outcome Variables | |||
Breastfeeding exclusivity | Current provision of only participant’s own milk to infant | Survey item adapted from Infant Feeding Practices Survey-II (IFPS-II) [34] | PP wk. 2 |
Breastfeeding self-efficacy | Sum scale score on instrument assessing extent of agreement with statements about breastfeeding confidence on Likert scale | Prenatal and Postpartum Breastfeeding Self-Efficacy Scale-SF [32]a (14 items) | Enrollment; PP wk. 2 |
Secondary Outcome Variables (*indicates an outcome that is also a mediating variable) | |||
Breastfeeding exclusivity | Estimated proportion of participant’s own milk feeds in: a) past week; and b) since birth (2 weeks pp); proportion of participant’s own milk feeds during birth center admittance; recall of infant age (days/weeks) to first formula use | Survey items adapted from Infant Feeding Practices Survey-II (IFPS-II) [34] and National Immunization Survey (NIS) [35]; electronic health record (EHR) | Birth center admittance; PP wks 2, 6, 12; 6 & 12 mos |
Breastfeeding duration | Current provision and birth center provision of participant’s own milk; recall of infant age when feeds of participant’s own milk ceased | Survey items adapted from NIS; birth center data abstracted from EHR | Birth center admittance; PP wks 2, 6, 12; 6 & 12 mos |
Breastfeeding self-efficacy | Sum scale score on instrument assessing extent of agreement with statements about breastfeeding confidence on Likert scale | Prenatal and Postpartum Breastfeeding Self-Efficacy Scale-SF [32]a (14 items) | Enrollment; PP wks, 6, 12 |
*Onset of lactogenesis II | Recall of lactogenesis II in post-birth days with item “When did your milk come in after your baby was born (i.e., when did you notice a big increase in the amount of milk)?” and answer options of “1 day or less,” “2 days,” “3 days,” “4 days,” “more than 4 days,” “my milk never came in,” and “unsure/don’t remember” | Survey item adapted from 2 items validated with infant test-weight data [36] | PP wk. 2 |
*Perceived milk supply | Sum subscale score on Likert scale instrument measuring perceived infant satisfaction with breastfeeding/breast milk received; Checklist item in problem list (“not enough milk”) and forced choice item classifying perception of milk supply ("too much," "about the right amount", or "not enough") | PIBSS subscale of H & H Lactation Scale (5 item) [33]; investigator-created items | PP wks 2, 6, 12 |
Interim prenatal breastfeeding confidence | Five-point Likert scale assessing agreement with single item, “I am feeling confident and well-prepared to breastfeed after my baby is born.” | Investigator-created item | At conclusion of each prenatal study visit, after intervention delivery |