Lisa, Hope this isn't too late to be helpful, have had family illness and not much time for Lactnet :( There are several interacting physiological mechanisms responsible for milk supply at different times in lactation. Not all are fully understood or studied, but here is the picture I have as of this moment: First 3 days- milk stim by deliv of the placenta, which removes it's prolactin inhibiting factor (PIF) and allows prolactin to act on the alveoli, stimulating them to rapidly increase milk production. First 6 weeks or so- prolactin receptor formation (theory)- the degree of breast stimulation and milk removal influences the number of prolactin receptors that proliferate on the milk gland cells. Receptors are neccessary for many things to enter cells, the more receptors, the more prolactin can enter the cell at once to stimulate milk production. This seems to be a critical phase, moms who begin to relactate in the first 6 weeks can be more successful than moms who start later, barring pressure induced atrophy from unrelieved engorgement. Degree of Milk Removal- this seems to work hand in hand with prolactin receptors to provide fine control of milk production from feeding to feeding. The more milk is removed from the breast, the less there is to cause feedback reduction of milk production rates. The theory is there is something in the milk itself that feeds back into the stimulation cycle, dampening it. This is active throughout lactation. This is the "autocrine control" theory. There is good experimental evidence that residual milk in the breast causes a reduction in the RATE of milk synthesis between feeds. Then there's the pressure induced atrophy, I suspect this is the emergency exit, the ejector seat- when a catastrophe prevents milk from being needed (fetal demise), the body digests the milk glands in response to unrelieved engorgement. Whether alveolar cells die from lack of blood supply (ischemia) and are then phagocytized (Jay- eaten up by white blood cells, specifically macrophages or "big mouths") or whether there is some other mechanism is not well studied, to my knowlege. My own feeling here is that all these control mechanisms work together to allow real fine tuning of milk supply. If the mom nurses early and often, and baby sucks well, she will develop good prolactin levels, higher calorie milk, more prolactin receptors, and keep all her alveoli by avoiding engorgement. I personally think that early engorgement is the most damaging of insults to supply, with lack of stim in the first few weeks being second. Milk supply seems to be more forgiving later in the process - witness all the weaning toddlers who go days in between nursings without mom losing supply. I usually tell moms that there is usually a better response to efforts to increase milk supply in the first 6 weeks, but that it is not hopeless thereafter. It's sometimes hard to walk that fence between encouraging someone to try and painting the picture either too rosy or too grey... In my practice, moms have regained full milk supplies if they began relactation efforts in the first 7 weeks postpartum. One mom with a 3 m.o. baby was nursing 3x/day and giving formula all other feeds, it took her a month to work up to exclusive bf, but there were suck issues involved as well. Another mom of a 4.5 mo old child had low supply secondary to suck problems, improving positioning and giving some specific oral support led to increase in milk supply/above avg weight gain, baby still nursing at 16 mos of age. These are the outer limits of my experience with developing and rebuilding milk supplies. There, now I've made up for being scarce for the past few weeks! Catherine Watson Genna, IBCLC NYC [log in to unmask]