An approach to low milk supply from pregnancy through the 4th B.  


So, first we need breasts that go through normal estrogen-mediated growth during puberty.  Then we need the pregnant breast to create the ducts, lobules and supporting structures to create milk.  These are created by prolactin, progesterone and chorionic gonadotropin (HCG-the thing that pregnancy tests check for). Breast growth in pregnancy, unlike puberty, has little to do with estrogen. 


Estrogen in pregnancy helps increase prolactin, the hormone that makes milk. The creation of milk also needs insulin, to help increase the number of supporting structures. Cortisol needs to be around to help with the formation of alveoli.


Breastmilk can be secreted by 16 weeks of gestation, but isn’t because milk secretion is held in check by progesterone and lactogen, both of which are formed by the placenta.  The receptors that help with making milk like both prolactin and placental lactogen, but usually the placental lactogen hogs most of them.


So, so far, we need adequate insulin and sensitivity to it, progesterone and lactogen (in other words, a working placenta), estrogen, prolactin, cortisol.  One of the questions we can ask when we approach low milk supply is “Did you experience breast growth during pregnancy?”  If we get “no” as an answer, we have several culprits.  Maybe the mother has hypoplastic (underdeveloped) breasts from puberty.  Perhaps we are dealing with poorly controlled diabetes which would affect insulin and its actions.  Maybe we have a mother with polycystic ovarian syndrome (PCOS) where the body doesn’t respond to insulin the way it’s supposed to. And there are many hormones that control prolactin.  An abnormality of any of them may impact supply.  If the answer to our breast growth question is “no” then we might need to set some realistic expectations for milk supply.  If we didn’t create the structures, we’ll have milk production issues.




The hormones responsible for the regulation of milk creation are oxytocin and prolactin.  Oxytocin is a product of the posterior (back part) pituitary gland.  Prolactin comes from the anterior (front) part of the pituitary gland. Oxytocin can be released under a variety of circumstances and doesn’t need direct suckling at the breast to work.  It is responsible for the milk ejection reflex (the “let-down”).  It can be inhibited by stress.  Cool plan.  If you were running away from tigers, you’d hardly want to be leaking milk behind you.  They could track you. 


Prolactin however is only released by stimulation of the breast.  The 4th intercostal (literally, “between ribs”) nerve is responsible for taking the information about suckling to the brain. Prolactin is the only hormone that is constantly prevented from being released.  Most hormones have a mechanism where if it gets too high, something lowers it.  Or if it gets too low, something increases it.  But not prolactin.  Dopamine keeps it in check until suckling begins.  The info from the nerve comes in, dopamine decreases and prolactin does its stuff.


Prolactin can be affected by insulin, cortisol, thyroid hormones, parathyroid hormones and growth hormone. So low milk supply issues here could come from insulin issues, again, or disorders of any of that list of hormones.  I often check thyroid hormones in mothers who have supply issues I can’t seem to get a handle on.


Low milk supply may also occur because of previous trauma (car accidents, biopsies…) or breast surgery that may impact the 4th intercostal nerve.  Breast reduction comes into play here because when they do that surgery, they often remove the nipple entirely (sorry for the visual) and those nerves are cut.  When that happens, the brain has a very, very hard time getting the suckling information from the breast and no prolactin would be released.  Those nerves do grow back, slowly. (We estimate about 1mm per year.)  If the mother has areolar sensation, we have a chance of achieving a milk supply, maybe not a full one (again, setting realistic expectations) but something.


Dopamine- enhancing medications, like many of the medications used to treat ADHD and the antidepressant/ smoking cessation medication Wellbutrin, may cause some decrease in supply because they increase dopamine, and therefore may decrease prolactin.


And tigers.  Define “tiger” however you’d like, but stress of any sort can inhibit the milk ejection reflex.  Alcohol can inhibit oxytocin as well.  Alcohol is another discussion however, so just know for milk supply purposes that it can make it hard to express milk.  I see that as a good plan actually.



The first several days


So during pregnancy, the cells that make up the structure of the breast are leaky- things can passbetween them. This also happens during episodes of mastitis and when you wean and the breast structures involute (go away) but that’s for another day.


At birth, those cells get lots less leaky.  The “gap junctions” close. That keeps sodium and chloride from getting in and lactose from getting out.  Over those next couple of days, lactose, which is a sugar, pulls water in with it and the milk “comes in” which is a term, as I have mentioned in other notes, that I really don’t like.


What makes this happen?  The placenta comes out and with it progesterone levels drop way down.  With progesterone gone, milk synthesis increases.  Cool.  Then we need insulin, prolactin and cortisol to continue production.  So, the milk secretion in the first few days is an endocrine process, not "demand and supply” until the 3rd or 4th day, when milk supply drops if the milk is not removed from the breast.  The baby still needs to nurse frequently and with a correct latch, get skin-to-skin and all those good things, but the process here is endocrine, so it’s very, very unusual for a mother to have “nothing.”  Colostrum can be secreted without the baby’s help.


Poor supply here?  Well, things that keep progesterone around, like retained placental fragments. And here’s where we would encourage women to be educated about Depo-provera as a contraceptive.  Depo is a progesterone hormone, maybe not the exact hormone that the placenta makes, but awfully close.  We have no idea who will have a drop in supply because of that Depo injection.  And as far as I know, we have no Depo-sucking machine that can get that 3- month injection out of your system if it does affect your supply.  If you choose to use contraception right after birth, and that’s up to you, we’d suggest that you try something like a progestin only pill that you can stop if it drops your supply.  Better yet, barrier methods might be better.    And kudos for wanting to have sex.


Again, insulin is very necessary here.  If the mother had insulin dependent or gestational diabetes or PCOS, we may see a delay in the transition to a larger milk supply.  If she needed metformin or other medication to get and stay pregnant, I usually encourage mothers to stay on it.


C-sections (which I’d place in the category of stress) may cause a delay in transitioning to a larger milk supply.  We’re not sure what the mechanism is here, but I would guess that the mom’s body is protecting her (she did just have abdominal surgery) before she tries to care for someone else.  I think post-partum heavy bleeding falls into this section as well.


After the first few days


Now we have demand and supply.  We need a good latch.  And if we have a poor supply here, the first things on the list are latch, latch, latch, get the point.  The more milk out, the more you get.  Poor supply here can come from any number of latch issues and things like tongue-tie or other baby anatomical issues like cleft lip and palate.


What’s the biggest factor here other than latch for poor supply?  Confidence. Which I talk about here.


We mess this up in every way we can.  My 3 “B”s -- birth weight, bilirubin and blood sugar-- come into play.  Maybe I need another “B”—bad advice.  We get something called “insufficient milk supply syndrome” in many women.  And yes, I’m an allopathic doctor- we named a disease process after confidence-rotting interventions.  This is where we need to support mom, give a consistent message, avoid supplementation, avoid  solid foods until 6 months and keep cheerleading, no matter who you are with relationship to that new mom.  




Jenny Thomas, MD, IBCLC, FAAP, FABM