Milk supply regulation

Maureen MinchinGeneral News

Milk production: an outline mums need to understand

The basics: appropriate hormonal stimulation + emptying of milk from breast

So, obviously
1. you need to allow baby to feed as needed, little and often to start;
2. feeding must be effective with no obstacles to milk drainage.

Stimulation creates and maintains a basal level of prolactin, essential to getting increases in supply from birth, and later if supply has dropped . (But by three months a happily breastfeeding mum’s basal prolactin levels are comparable to a non –lactating mum – it is the repeated bouts of sucking-stimulated prolactin level rises that does the job of enabling lactose and so milk production, with prolactin returning to baseline in between if intervals allow).

Initially breasts overproduce on autopilot, and subsequently milk supply drops down to the volume of milk drained from the breast on a daily basis. Lactation is energetically expensive, and throughout human history women have never been able to afford to waste energy, in many cultures eating last and least. So volume is regulated by need, which is measured by what is taken, and the breast responds rapidly (but not instantly) to any change in demand. How?

Regulatory controls are twofold, within the breast itself (autocrine). Firstly, if a feedback chemical (FIL, feedback inhibitor of lactation) reaches a certain level in the breast, it signals that milk is not needed, and milk secretion is inhibited, and eventually stops.

The second internal down-regulator is high pressure. If enough pressure flattens the rectangular-ish secreting cells, then they stop work; over time they can regress and disappear. That pressure can be local, or a whole breast, pressure. So habitual finger pressure that prevents drainage from one area, or an underwire bra that sticks into a particular spot, or surgical scarring, or a tight crop top, can have an effect. As can over-distension of the whole breast because of too long a gap between feeds from a breast. Or pressure from sleeping/lying on one’s stomach, OK for some mums, hopeless for others (if having a massage, it might be best not to be too long facedown, and much massage can be done seated). If pressure gets high enough, it not only squashes the secretory cells, it can cause milk from the ducts and cells to leak into surrounding tissues and trigger inflammation. (Mastitis is breast inflammation, NOT necessarily due to infection) (So feed before any massage, time appointments for the afternoon preferably; be prepared for some leakage. Towels and large absorbent pads in bed can be useful, save bed changes..)

How does milk flow out?

Milk is made continuously, and is mostly water based, with about 7% cream. (Fat is the most variable component of milk, and babies drink less by volume of a rich creamy milk.) The watery part of the milk flows out of the manufacturing cells rapidly, while the fat has to be extruded, sort of squeezed out by the cell into that aqueous fluid. The oxytocin release triggered by suckling contracts tiny muscles around those cells and pushes milk out into the ducts (the let down).

A vacuum in the baby’s mouth is created when the baby’s jaw drops and baby sucks. The seal needed for making a vacuum is created by tongue, cheek pads, and upper gum ridge etc. The vacuum – lower pressure area – allows milk to flow out from the breast – a higher pressure area with letdown pushing milk out, as warmth from the baby’s mouth relaxes a little ring of muscle that contracted stops milk outflow. (In some mums at some times it doesn’t stop the outflow, so they ‘leak’.)

Cream in milk

The relative amount of calorie-rich cream in milk varies over a feed, between feeds, between breasts, over the day, over time, following the general rule that the emptier the breast and the more letdowns it has been exposed to, the higher the fat levels. So after any interfeed interval, milk from the start of the first breast is ‘waterier’ than the milk at the start of the second breast will be, because the second breast has had oxytocin squeezes while the first is being fed from. And swapping back to the first breast after the second can mean an even richer milk again. Babies can be trusted to know when they are satisfied, and it sometimes takes the extra cream of a ‘third’ breast to do so. Or a ‘fourth’!

Breast storage capacity, feed intervals, amounts

Once lactation is established, the interfeed intervals are heavily influenced by the interaction between breast storage volume, and infant stomach volume. Over a day a baby takes an average of about 750mL. A breast with storage capacity of 800mL could theoretically mean one feed a day, except that a baby’s stomach capacity won’t allow that!

SO: a breast with very small storage volume will mean more frequent feeds at shorter intervals.

So too does a small tummy. A baby with a big stomach means fewer feeds per day if the mum’s storage capacity allows that tummy to be filled up (it can even get down to 3-4 feeds in 24 hours in some thriving babies under 6 months old.) It’s said that the size of the baby’s stomach is roughly the size of its fist, but it can be distended comfortably. (If over-distended the baby will blurt back the extra – sometimes too much comes up, so yet another feed is indicated to settle things.) Being creamy, sometimes only a few extra mouthfuls are needed to get bub to drop off looking milk-drunk.

Rates of milk making and breast filling

Rates of milk synthesis vary over the day, and are governed by the degree of breast fullness. When the breast is close to its residual baseline (it’s never truly empty), synthesis rates are faster. When breasts are fuller, synthesis rates are slower. The small breast that empties quickly also refills quickly.

During the night sleep, longer intervals and higher-at-night prolactin levels combine to produce a full breast by morning. Take out a single feed then, and refilling will be slow: the 600mL capacity breast might have dropped to 500mL, but there’s still plenty there, so no rush to refill. By the next feed a few hours later,  volume might be back to 540mL, and drop down to 450 after that feed. Over the day, by evening some mums can  come close to running on empty, with baby staying at breast and drinking pretty much as milk is produced. That milk may move from the stomach on into the small intestine at much the same rate, so baby doesn’t get that satisfactory FULL STOMACH feedback signal and either fall off looking drunk, or else sleep for a short time but wake up and want more. [There’s stuff that could be said here about gastric hormones and signalling, but no need.]

Working with this knowledge

If you take out a lot of milk at the first morning feed, by simultaneously feeding on one side and pumping the other breast, (afterwards letting baby have the second side for as long as wanted) and milk synthesis rates speed up to replace milk in both breasts. The suckling baby triggers letdown in both breasts, and both are well drained. So this is the ideal time to express milk for storage or as a reserve. And having a small frozen stash of milk IS a good idea as  it provides reassurance that baby won’t starve if for some reason supply drops. That lowers maternal anxiety levels and so can become a positive factor for continued lactation, which can be influenced by stress. (Though remember that lactation IS a survival mechanism, and stress has to be extreme before it will suppress lactation – and most women reading this will never experience that sort of distress. In times of war and disaster breastfeeding rates are higher, not lower, and there could be few stresses greater than war!)

While it’s good to have a small stash for a range of reasons, don’t be persuaded to think about expressing after every feed, unless it’s for a medical reason. Doing so creates too much work, keeps breasts cold, and is a real pain, leaving little time for rest and sleep and enjoying baby. And while you would later freeze that extra expressed morning milk, it can be stored in the fridge during the day till it’s clear there’s enough been made to keep baby full that day; if not, you can pour off some and feed it to baby by spoon, cup, syringe, whatever.

I developed this strategy to deal with what I called six o’clock starvation, when I just could not satisfy baby no 3 with a full feed in the evening. Before I tried this, I had to keep her at breast for hours, contentedly getting small dribs of milk but dozing, refusing to leave or drop off to sleep. Topping baby up in the evening with some of the morning milk meant she went off to sleep, my empty breasts refilled before she woke again a few hours later, and in between I got my other two kids to bed and cleaned up. Then she had a full feed and dropped off back to sleep for a long time, and I went to bed!

For early morning one-breast expression like this, the Kaneson pump came in handy. It’s a simple silent no-strain one-handed pump: draw back the outer cylinder a tiny bit to create the slight suction needed to relax the ring of muscle around the nipple, and milk pours out of the second breast when oxytocin hits both breasts and triggers letdown). (Any small one-handed pump can be used except the old rubber bulb variety, which is a microbial nightmare).

But not until mums are comfortably feeding and can multi-task should they think about trying this morning expression technique. Getting position and attachment right, so that baby can feed well and breasts produce well is the first priority. When mums can feed and drink a cuppa, they can do one-handed expression no trouble. If they want to get milk to store. Or to give an older child a glass, or make breastmilk ice blocks. Or to donate. Or whatever it’s needed for.

Warmth and breasts

Breasts being extremities like fingers and toes, they are colder than other parts of the body. They need to be warm for vigorous blood circulation to bring in lots of nutrients for milk making. Simple things like hotpacks or having a small patch of wool, silk or fleece to tuck into the bra around the breast not in use can make a difference to refilling rates. So can an afternoon nap. I never ran dry on days when I snuggled down with a baby and had a full-body after-lunch rest. I always ran dry by evening if I worked through the day and only sat down for feeds.

Some mums can cope with strenuous exercise and still lactate successfully; others can’t. (Babies don’t like the taste in milk of lactic acid created by strenuous exercise, but it disappears after about 30 minutes.)

Increasing milk supply

So increasing milk production means increasing sucking stimulus, and frequency, increasing synthesis rates by breast emptying, and decreasing any competing activities. In short, go to bed with baby and sleep and feed feed feed, and (optional) express first thing in the am. After 2 days of more frequent feeding, basal prolactin levels rise – they may have fallen too far – and milk-making increases. A babymoon it’s sometimes called. Not possible for many mums with children and dogs and household tasks. Using drugs to increase prolactin has its risks and in any case will not work if the problem is insufficient breast emptying and natural feedback down-regulation of supply. Raising prolactin is useful only when prolactin is low, and it can be done by lots more feeding and holding and carrying baby, and by cuddles with children and partners. It is more common where mother and baby are separated, as in neonatal units that are not updating to provide routine skin-to-skin contact for infants.

Decreasing milk supply

Decreasing milk production is equally simple. Increase intervals between feeds, for example by one-breast feeding with only short times on the second breast, back to the emptier first breast for a couple of hours, monitoring the unsuckled breast and expressing only to comfort and to avoid mastitis. Within 24-48 hours of one-breast feeding supply will drop, sometimes catastrophically. It’s disaster to suggest this to new mums with oversupply, as many hospital-based midwives have done. The mums go on for more than 24-48 hours and then wonder why their milk has gone. Lying face down compressing boobs, wearing a tight crop top or bra, creating pressure feedback, and you may achieve the same outcome via mastitis. (In a breast with no skin damage, most mastitis starts with milk leaking into breast tissue where it shouldn’t be, under pressure.)

The feel of the working breast

Mums need to know what an efficient working breast feels like: soft and flexible even when heavy with milk, filling up, softening again after a feed; maybe tight and tense to touch if the interval is too long but immediately relieved by milk removal. Warm but not heated, not reddened skin. Not lumpy, even up in the armpits where there is some glandular tissue in many women. There’s always a reason for any change in breasts and thinking though exactly what’s happened can find it, and prevent recurrences.

Further reading

There is a lot more in Breastfeeding Matters 1998 edition that would be of interest and relevance, in chapters on milk supply, nipple problems and mastitis.. I’ll gradually post these online, though a copy of the book can still be obtained direct from me for A$20 posted in Australia (most of that is postal costs).

Breastfeeding is a skill that has to be learned, and without early practical support and a good understanding of how supply is regulated, women will struggle. Any mother who has been told to feed just one breast per feed is at risk of undersupply, and mother who has been told always to feed both breasts may be at risk of oversupply. Mums get confused because what is said by one adviser is apparently contradicted by another adviser. Yet both suggestions have a reason and consequences. This is why it is the mother who needs to understand how her breasts work, and when to do what patterns of feeding to regulate supply to demand.