1) Lactogenesis I
Lactogenesis I is when the breasts make colostrum. This starts as early as 16 weeks and as late as 22 weeks into pregnancy (Lawrence 2016).
2) Lactogenesis II
Lactogenesis II is when the breasts change from making colostrum to making transitional milk.
The placenta makes the hormone progesterone, which blocks the action of prolactin, one of the hormones needed to start milk production. When the mother delivers the placenta, the level of progesterone quickly falls triggering lactogenesis II (Ostrom 1990).
Mothers will start making milk 24 to 96 hours (average 60 hours) after delivery. This is also called milk “coming in” or secretory activation. The amount of transitional milk is much larger than that of colostrum and as a result most mothers will notice definite changes in their breasts as the milk comes in.
The first feed at the breast should be within one hour after birth. If breastfeeding is not possible, mothers should express within one hour after birth. From then, milk must regularly be removed from the breast for it to maximize the amount of milk made. This can be done by effective breastfeeding or regular, effective expressing.
The amount of milk made over the long term depends very much on establishing milk production within the first two weeks. During this time, milk cells lining the alveoli and the number of prolactin receptors on these cells increase in number (Meier 2012).
3) Lactogenesis III
Lactogenesis III is when the breast makes steady amounts of mature milk. This starts in the third week after birth and continues until weaning starts. On-going milk production needs regular milk removal.
4) Lactogenesis IV
Lactogenesis IV is when the breast stops making milk as weaning happens. Weaning milk has differences in some of the nutrients compared to mature milk. Weaning can proceed at different rates and this will determine how long milk continues to be produced by the breast.