Abstract
Background: Breastfeeding is widely recognised as the optimal source of infant nutrition, offering extensive health, developmental, and relational benefits for both mother and infant. Despite this, exclusive breastfeeding rates in New Zealand and globally remain lower than the World Health Organization's recommendation of six months. A leading reason for early cessation of breastfeeding is Perceived Insufficient Milk Supply (PIMS), where mothers believe they are unable to produce enough breast milk to meet their infant's needs, regardless of whether actual insufficiency is present. Perceived Insufficient Milk Supply is most often reported in the first four months postpartum, a period characterised by a mother's physiological adaptation to breastfeeding, learning to feed their infant effectively, and strong social influences. Less is known about mothers with a perception of excess milk supply (herein coined 'PEMS'). Mothers who report PEMS may experience physical discomfort, breast engorgement, mastitis, or a fast let-down reflex, which the Candidate hypothesises may contribute to feeding difficulties that could drive early cessation of breastfeeding, as with PIMS. While research has consistently identified PIMS as a key determinant of breastfeeding cessation, less is known about how any perceptions of milk supply evolve across the early postpartum period and how experiences and external influences may affect maternal confidence in continued breastfeeding decisions.
Aim: To determine the prevalence of PIMS and PEMS in exclusively and fully breastfeeding New Zealand women between birth and four months postpartum, and to describe their breastfeeding experiences and perceptions in the context of breast milk supply between birth and four months postpartum.
Methods: The Māma and Baby Breastfeeding Study (MABBS) was a cross-sectional study conducted in Dunedin (New Zealand). This thesis used a subset of demographic and questionnaire data from fully breastfed infants aged 3 to <4 months and their mothers. Mothers' current perceptions of breast milk supply were assessed at a first visit of five, using a question developed by the research team and answered on a 5-point Likert scale. Responses 1 and 2 were classified as a perception of 'low milk supply' (i.e. PIMS), and responses 4 or 5 indicated a perception of 'high milk supply' (i.e. PEMS). Previous concerns about supply for this infant (from birth to less than 4 months postpartum) were categorised similarly based on maternal responses. If participants selected 'yes' to having had concerns previously about their breast milk supply, they were asked to select from 'not enough milk', 'too much milk', or 'other'. Mothers were classified as perceiving their milk supply to be high or to be low based on their respective responses. The questionnaire also included open-ended questions asking mothers with low or high supply concerns to describe the reasons why they felt that way about their breast milk supply. Quantitative data were analysed using Stata SE and Microsoft Excel; qualitative responses were thematically analysed in NVivo.
Results: The prevalence of any experience of PIMS or PEMS was the same: 16 out of 48 participants (33.3% each). Of mothers who had experienced PIMS, most had concerns at 1-2 months postpartum (56.3%), while 37.5% were experiencing it at the time of participation.
Among mothers who had experienced PEMS, most concerns about excess milk supply arose between 2-3 months postpartum (93.8%). At the time of participation, 75.0% were experiencing PEMS.
Four themes were generated from the responses of mothers who had experienced PIMS: 1) Breast milk quantity diverged from mothers' idea of the norm, 2) Infant behaviours triggered concerns about reduced breastfeeding quality, 3) Mothers felt health professionals prioritised standard advice over individual needs, and 4) Grandparents' input led mothers to doubt their breastfeeding decisions. Two themes were generated from the responses of mothers who had experienced PEMS: 1) Mothers perceived problematic infant behaviours during fast letdown, and 2) Mothers felt discomfort when their breast milk supply exceeded their infant's feeding needs.
Conclusions: While PIMS has been described in previous literature, this study is the first to conceptualise PEMS as a distinct phenomenon within the breastfeeding experience. Across both groups, mothers' perceptions of their milk supply were shaped by how they interpreted their infants' feeding behaviours and physical reactions during breastfeeding. Family members, particularly mothers and mothers-in-law, were also prominent in shaping maternal breastfeeding experiences through comments or advice that reinforced mothers' feeding challenges. Although midwives and Well Child nurses were generally viewed as trusted support people, this study suggests that the framing of their communication may be influential on mothers' perception of their milk supply. While PIMS has now been widely recognised as a key predictor of early breastfeeding cessation, the parallels observed in this study suggest that PEMS may have replicable implications if its associated challenges are not adequately addressed and supported. Longitudinal research examining the feeding trajectories of women experiencing PEMS and its associated challenges would be beneficial in clarifying the possibility of a clinically significant relationship between Perceived Excess Milk Supply and the prevalence of early breastfeeding cessation.