Table 1.

Outcome measures and potential covariates with breastfeeding self-efficacy and breastfeeding outcomes

Measure	Time point	Description
Primary outcome
Modified Breastfeeding Self-Efficacy Scale - Short Form [20]	Baseline; Discharge	18-item scale validated for mothers of ill and/or preterm infants. Assesses a mother’s confidence in her ability to breastfeed. Internal consistency (0.88) is high.
Secondary outcome
Breastmilk feeding	Baseline; Discharge	Labbok and Krasovek [41] classification system, modified to include additives and fortification. 24-h maternal recall.
Co-variates and potential confounders
Parental Stressor Scale: NICU [62]	Baseline; Discharge	50-item scale that captures parental perceptions of stress in the NICU: (1) sights and sounds; (2) appearance and behaviour of the infant; (3) impact on the parental role and relationship with the infant; and (4) parental relationship and communications with staff. Internal consistency (0.89 to 0.94 for the total scale) and test-retest (0.87) reliabilities are high. Potential confounding: Decreasing maternal anxiety and stress may have a physiologic impact on breastmilk production [63, 64].
Edinburgh Postnatal Depression Scale [65]	Baseline; Discharge	The most commonly used pre- and post-natal depression screener validated for mothers. Consists of 10 items and has a sensitivity of 0.86 and specificity of 0.78, with a positive predictive value of 73%. Potential confounding: Successful breastfeeding is predictive of lower maternal depressive symptomology. Depressive symptoms may be predictive of reduced breastfeeding rates [66].
State-Trait Anxiety Inventory [67]a	Baseline; Discharge	40-item scale that captures dispositional/trait anxiety (20 items) and current state anxiety (20 items). Internal consistency (0.86 to 0.95) and test-retest (0.73 to 0.86) reliabilities are high. Scores on the STAI and PSS: NICU are correlated [62]. Potential confounding: Mothers who demonstrate high rates of anxiety or depressive symptomology routinely have lower breastfeeding rates than mothers that do not [66].
Perceived Maternal Parenting Self-Efficacy scale [68]	Baseline; Discharge	20-item measure of parenting self-efficacy validated for mothers of preterm infants. Captures maternal perceptions of ability to (1) give basic care; (2) elicit change in infant behaviour; (3) recognize infant behaviour; and (4) judge interactions with her infant. Exploratory factor analysis confirms four factors; internal consistency (0.91) and test-retest (0.96) reliabilities are high. Potential confounding: Concurrent validity between general self-efficacy and BSES-SF [22].

^aAt admission, both State and Trait forms are completed; at discharge only State form is completed. Adapted from Benzies et al. [30]