Maternal perceptions of human milk expression output: An experimental design using photographs of milk

The widespread use of breast pumps in the United States is a recent phenomenon that is reshaping how individuals understand and perceive lactation. In the 1990s, adequacy of milk supply was primarily measured indirectly by infant weight gain and/or diapers; now >95% of all lactating persons in the United States use breast pumps and are seeing their milk regularly. How seeing milk impacts the perception of lactation sufficiency is an important area of research. Research aim/question: To understand personal and intersubjective influences of seeing expressed human milk on perceptions of milk supply among participants who express milk for their infants.

We surveyed 805 lactating participants from the United States about their pumping practices using an online survey. Participants described pumping practices, milk output, and beliefs. They were then randomized to view one of three photographs of expressed milk (<2 oz, 4 oz, >6oz) and asked to imagine they had just pumped that amount and provide a written response; this created 4 exposure groups (2 increase and 2 decrease) and a control group (no difference).

Participants randomized to a higher volume reported more positive feelings and used the terms "good", "great", and "accomplished" to describe emotional responses to output. Participants randomized to lower milk volumes reported more feelings of "bad" or "depressed." A subset of participants reported feeling "annoyed" about small volumes of milk.

Participants in this study were very conscious of the volume of milk pumped each session; both increases and decreases were associated with emotional responses that could contribute to decisions about pumping practices, perceived milk supply, and lactation duration.