What is delayed secretory activation?

Delayed onset of lactation is a commonly used term, but is scientifically inaccurate, since lactation commences during pregnancy, with secretory differentiation. You can read about lactogenesis here. The more accurate term is delayed onset of secretory activation.

Delayed onset of secretory activation is independently associated with shorter breastfeeding duration. It is currently defined as the milk coming in later than 72 hours after delivery.

However, research has shown that secretory activation may occur up to five days postbirth in otherwise well women who go on to breastfeed successfully, and this tension between prevailing definitions and research findings need to be borne in mind by the clinician.

How do we measure onset of secretory activation?

Women's own physical experience of her milk coming in has been shown to be a reliable indicator of secretory activation.

• She feels physical symptoms 24 hours after the changes which herald transitional milk can be measured in her colostrum.

• Some women won't have a feeling of the milk coming in because they are feeding frequently and flexibly.

• Other women who feed frequently and flexibly experience engorgement. The engorgement acts as a brake on a genetically generous milk production.

What are risk factors for delayed secretory activation?

Risk factors for delayed onset of secretory activation include

• Primiparity

• High maternal body mass index

• Diabetes

• Other metabolic conditions

• Obstetric complications

  • Caesarean birth

  • Postpartum haemorrhage

• Suboptimal infant breastfeeding behaviours resulting in impaired milk transfer.

Are programmed endocrine factors or environmental factors more important in determining when women report that their milk comes in?

The relative contribution that milk removal and effective suckling make to delayed secretory activation is unclear.

• One perspective is that milk removal is not needed for the programmed physiological changes that bring about secretory activation.

• However, other studies have found that prelacteal formula feeding is associated with delayed onset of secretory activation.

In my view, both endocrine programming post-birth, genetic factors, and environmental factors are interacting in the complex system of the mother and baby immediately post-birth. Secretory activation is a programmed and endocrine controlled event. However,

• The amount of milk produced as an endocrine controlled event may be strongly influenced by genetic factors.

• Modulation of amount of milk produced with secretory activation is impacted by environmental factors, most powerfully, the effect of frequent flexible milk removal from birth.

What is the prevalence of delayed onset of secretory activation?

A 2007 Australian study of 453 Australian women by Scott et al found an incidence of 11.7% of delayed onset of lactation, using the 72 hour definition, which is much lower than reported for women in the USA (22-35%). This suggests that delayed onset of lactation is modifiable according to cultural practices of birth and infant feeding.

In the 2007 Australian study there was no independent association between delayed onset of secretory activation and formula use, length of time after birth before the infant was put to breast, or any other factors which may promote or interfere with effective suckling. This study also suggests that it is normal for primiparous mothers to experience breast fullness after 72 hours.

Selected references

Moorhead A, Forster DA, Donath SM. Does antenatal expressing affect onset of lactogenesis for women with diabetes? Results from a randomised controlled trial and cohort study. ANZJOB. 2024:https://doi.org/10.1111/ajo.13929.

Scott JA, Binns CW, Oddy WH. Predictors of delayed onset of lactation. Maternal and Child Nutrition. 2007;3:186-193.

Spatz D, Rodriguez SA, Benjilany S. Having enough milk to sustain a lactation journey: a call to action. Nursing for Women's Health. 2024;28(4):256-262.