Sometimes we just don't know what may have undermined a mother's ability to
lactate.  Recently worked with a mom who breastfed her first baby with
complete success.  Six years later she could produce only 2 oz q24h.  No
history of surgery or illness in the intervening years.

Possibilities -

1.  Insufficient glandular tissue
Should be considered when breasts very asymmetrical.  Sometimes very small --
seem frozen at adolescent stage - widely separated at base.  Sometimes
tubular -- narrow at base and perhaps wider at areola.

2.  Surgery
Sometimes even a biopsy can do damage to the biopsied brease.  Reduction is
almost always a problem.  Augumentation is suspect when the incision is
periareolar.

3.  Insufficient emptying in first 72 hours
I understand the mechanism at work here very poorly but have definitely seen
the results in terms of low or almost zero milk production.  Relates to
"mammary epithelial cell tight junction integrity".  Tight junctions are
supposed to occur in first 48 hours in response to emptying of colostrum.
 Alveoli subsequently produce high quantities of lactose and fat.  When these
tight junctions do not occur alveoli continue to secrete low quantities of a
high sodium milk.  May be irreversible.

Reviewed my records recently for some women who had very low milk production
despite frequent nursing and noticed that each time I had assessed a poor
latch (usually tongue under nipple not cupping areola) with unusual weight
loss (excess of 10%).

I don't accept that "latch is good" unless I have seen it myself.  I have
heard over and over again "the nurse said my latch is fine" and found that,
though things superficially look ok, baby is not latched in a way that allows
emptying of the lacteal sinuses.  It's not how it looks -- it's whether the
baby is swallowing that counts.

4.  Thyroid disease

Hope this helps.
Joanna Koch IBCLC in Los Altos, Ca