While acute iron-deficiency anemia brought on by a significant postpartum
blood loss could play a role in delayed lactogenesis, it need not do so.
(Anemic women have been shown to be at greater risk of mastitis, however.) 
I think the delay may be a combination of direct effects on fluid and
colloid balance after blood loss, and indirect effects such as someone else
taking over care of the baby to let the mother rest, depriving the breasts
of stimulation which drives supply.

Sheehan's syndrome is a serious, permanent endocrine disorder involving
necrosis of the anterior pituitary gland, following hypoxic injury due to
shock.  It is not the drop in hemoglobin, but the drop in blood pressure
accompanying a serious postpartum hemorrhage which causes the problem.  In
classic Sheehan's syndrome, lactogenesis 2 is not delayed, it is absent.
There is no prolactin produced at all. The posterior pituitary (oxytocin),
consistent with its different histology and function, has a separate
vascular system from the anterior and is not affected by shock in the same way.

I've worked with numerous women who have experienced postpartum blood losses
of several liters who have established a normal milk supply by breastfeeding
like anyone else, and some who have struggled to maintain their supplies.
Don't think I have seen a case of Sheehan's yet, though I know of a woman
who survived an amniotic fluid embolism and DIC, involving complete
circulatory collapse, who did not go on to breastfeed.  I believe she was
given cabergoline and I don't know all the details, but she would have been
at high risk for Sheehan's.  It's an extreme situation and not one you are
likely to see if you work in a hospital with trained birth attendants and
high-level emergency care.

Rachel Myr
Kristiansand, Norway

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