Dysphoric Milk Ejection Reflex: Measurement, Prevalence, Clinical Features, Maternal Mental Health, and Mother–Infant Bonding

<b><i>Introduction:</i></b> Dysphoric milk ejection reflex (D-MER) is a condition affecting lactating women, characterized by abrupt emotions of dysphoria that start shortly before or during milk let-down and progress for several minutes. Research on D-MER, especially with quantitative methodology, is minimal. This study aimed to validate an instrument for D-MER-related emotions, examine its prevalence and clinical features, and explore differences in maternal mental health and mother-infant bonding between mothers with and without D-MER. <b><i>Methods:</i></b> A total of 711 women up to 12 months postpartum participated in an online cross-sectional study. Participants fulfilled the D-MER Questionnaire (D-MERq), Edinburgh Postnatal Depression Scale, Depression, Anxiety, and Stress Scales, and the Postpartum Bonding Questionnaire. <b><i>Results:</i></b> The analysis showed that D-MERq had high reliability and good discriminant and divergent validity. The prevalence of D-MER was 5.9%. For the majority, D-MER manifested intensely, accompanied mostly by agitation- and anxiety-related emotions, and 45% of mothers discontinued breastfeeding due to D-MER. Mothers experiencing D-MER had higher levels of depression, anxiety, stress, previous psychiatric diagnoses, and more mother-infant bonding difficulties compared with mothers without D-MER. <b><i>Conclusion:</i></b> These findings demonstrate that D-MERq is a valuable tool with good psychometric properties and suitable for clinical and research use to facilitate early identification and better understanding of this phenomenon. D-MER affects a noteworthy number of women and is associated with impaired mental health, bonding difficulties, and breastfeeding discontinuation. This highlights the importance of health care providers recognizing D-MER to ensure better outcomes and a more positive breastfeeding experience.