Critical Factors in Milk Production

It is very important for all women to understand the basics of lactation whether she is breastfeeding or pumping; and perhaps more important for women who are pumping. What follows are some of the keys aspects of milk production that are critical to understand when exclusively pumping. Understanding how lactation is initiated and regulated can help you establish a strong milk supply and maintain that supply with a breast pump.

Stages of Lactation

Lactogenesis I begins during pregnancy. The mammary glands change from inactive to active preparing for lactation. About half-way through pregnancy, the breasts will begin to produce colostrum. You may or may not experience leaking at this time. Breasts usually enlarge, veins become darker, the areolas enlarge and darken, and the nipples become more erect.

Lactogenesis II begins following the detachment of the placenta. This stage of lactation is triggered by the sharp decline in progesterone following the delivery of the placenta. Any retained placenta can greatly impact a mother’s ability to establish a full milk supply. Colostrum is present at birth and is all a baby requires until milk production increases. Colostrum is high in antibodies and protein, has a laxative effect assisting baby in removing meconium from her system, and coats the gut providing protection from potential pathogens. Formula provided during this time (even just once) changes the normal flora of the gut and it takes days for it to return to normal.

Milk production slowly increases over the first few days post-partum. It usually takes 2-5 days for milk volumes to increase, but it can take longer depending on certain factors. First time mothers will see an increase later than mothers with previous children.

Milk will slowly transition from colostrum to mature milk. Mature milk will usually have a bluish colour but can vary in colour due to mother’s diet. Breast milk is usually quite thin and watery and will separate if expressed and left to sit. It is important to realize that lactogenesis II will happen regardless of whether a woman is choosing to nurse her baby or not since it is a result of hormonal factors.

Hormones Involved (oxytocin and prolactin)

Prolactin--Prolactin is the hormone responsible for triggering milk production. It is also referred to as a “mothering hormone” because it creates mothering responses. Prolactin levels rise sharply following delivery and falls substantially over the first 24-36 hours post-partum. Prolactin is produced by the anterior pituitary gland and causes a decrease in estrogen levels. Levels of this hormone vary throughout the day with highest levels at night; hence the reason why it is so important to pump around the clock and during the night.

Once lactation is established prolactin takes on only a permissive role and opposed to a regulatory role meaning that it no longer drives production but its presence simply allows milk production to continue.

Oxytocin--Oxytocin is vital during both the birthing process (contractions) and lactation (milk ejection reflex). It is also a “loving hormone” assisting in creating affection and social bonds with others.Oxytocin can help to create a relaxed, calm, and euphoric feeling which both the mother and baby experience. Oxytocin is important to the bonding of mother and baby and in the presence of prolactin helps to create a strong bond between mom and baby. Oxytocin levels in the brain soar immediately after delivery- one reason why immediate and uninterrupted one-on-one time following a baby’s birth is so important.

Endocrine and Autocrine Control

Endocrine control refers to the hormonally driven stage of lactation- Lactogenesis II- which will happen regardless of whether a baby is nursing or not. During this time, lactation is established and supply is set. Production will vary depending on stimulation and frequency (i.e different for singleton baby than for twins). And for this reason, it is vitally important whether pumping or breastfeeding that pumping or breastfeeding happens frequently.

Autocrine (local) control is also referred to as lactogenesis III and is the maintenance stage of lactation. This is the process of supply and demand. Milk synthesis is controlled at the breast.

Milk removal is the primary control mechanism for milk supply. It is important to understand current knowledge of milk synthesis. Important aspects of milk production follow: Milk production slows as the breast fills! There are two reasons for this:

  1. Protein in breast milk called Feedback Inhibitor of Lactation (FIL). Therefore as the breast fills, more FIL is present, and production slows. Think of a grocery conveyor belt. As you put groceries onto the belt, you have less and less room to add more and eventually you must stop adding anything because you have run out of room. In order to allow more groceries to be added- or breast milk produced- you must remove some of the groceries- or milk.

  1. When the alveoli (small sacs that contain milk producing cells) are full of milk, their walls expand and the shape of the prolactin receptors change. This does not allow prolactin to enter at these sites and, as a result, slows milk production. As the alveoli empty, the receptors return to their normal shape allowing prolactin to enter and milk production to increase.

The Prolactin Receptor Theory is also an important concept in lactation and has important implications for the exclusively pumping mom. The basic idea of the prolactin receptor theory is that milk production is “set” during the first few days/weeks post-partum. Frequent stimulation increases the number of prolactin receptors in the breast allowing the body to utilize prolactin in the body more effectively. This sets the milk production for the rest of lactation period. Babies naturally feed for short periods but very frequently. This encourages the increase of prolactin receptors and the establishment of a strong milk supply. For mothers who are using a breast pump to initiate their milk supply, it is vitally important to understand this concept of the Prolactin Receptor Theory and ensure a pumping schedule that is provide frequent stimulation and removal of milk.

Storage Capacity and Milk Production

Storage capacity is the amount of milk the breast can hold between nursing or pumping sessions. Storage capacity is not directly related to the size of the breast and can differ between breasts. Storage capacity of the breast impacts the rate of milk production. A large storage capacity will allow milk production to continue on before slowing since the receptors will not “stretch” until full. This has a direct impact on pumping schedules and explains why some women are able to pump relatively infrequently while maintaining a strong supply and yet others must continue to pump frequently throughout their time exclusively pumping in order to maintain a basic level of production. Your storage capacity will directly impact a baby’s feeding pattern if the baby is directly nursing, but as a mother who is pumping, you need to understand how your own storage capacity will affect your pumping schedule.

Think of this concept as a cup--you can drink a large amount of water throughout the day using any size of cup. If you use a small cup you will simply have to refill more often. This is not an indication that a woman with a larger storage capacity can produce more milk, only that a woman with a smaller storage capacity will need to pump more frequently.

Fat Content

The concept of foremilk and hindmilk is a rather outdated concept. Research has shown that fat is released into milk as the breast empties. A baby fed from a full breast will have an increasing amount of fat as the breast empties and a baby fed from a less full breast will have a more consistent level of fat throughout feed. Likewise, milk that is pumped from a full breast will have an increasing amount of fat as the breast empties. You will notice the milk that is first expressed is thinner and waterier. And milk that is expressed from a breast that is not exceedingly full will have a fairly consistent level of fat throughout the pumping session. A baby’s intake and not the amount of fat in breast milk is the ONLY thing that has been connected to infant growth. As long as you are pumping frequently and emptying the breasts as fully as possible during each pumping session, you really do not need to be worrying about fat content of your breast milk.

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