Breastfeeding: Encyclopedia II - Breastfeeding - Beginning lactation

Breastfeeding - Beginning lactation

Main article: Breast milk

Throughout the last two trimesters of pregnancy a woman's body produces hormones which stimulate the growth of the milk duct system in the breasts:

• Progesterone -- influences the growth in size of alveoli and lobes. Progesterone levels drop along with estrogen levels after birth, triggering the onset of copious milk secretion. (Mohrbacher, IBCLC, Nancy; Stock, MA, IBCLC, Julie (2003). The Breastfeeding Answer Book, Third Revised Edition. La Leche League International, Inc. ISBN 0-912500-92-1)
• Estrogen -- stimulates the ductule system to grow and become specific. Estrogen levels drop at delivery and remain low for the first several months of breastfeeding. (Ibid) (This is also why it is recommended that breastfeeding moms avoid estrogen-based birth control methods while they are planning to breastfeed. A spike in estrogen levels compromises a mother's milk supply level.)
• Follicle stimulating hormone (FSH)
• Luteinizing hormone (LH)
• Prolactin -- contributes to the accelerated growth of the alveoli during pregnancy (Rilemma 1994).
• Oxytocin -- contracts the smooth muscle of the uterus during birth, after birth, and during orgasm. After birth, oxytocin contracts the smooth muscle layer of band-like cells surrounding the alveoli to squeeze the newly-produced milk into the duct system. Oxytocin is necessary for a let-down, or milk ejection reflex, to occur. (Ibid)
• Human placental lactogen (HPL) -- HPL is released in large amounts by the placentra during pregnancy (beginning in the second month) that appears to be instumental in breast, nipple, and areolar growth before birth. (Ibid)

By the fifth or sixth month of pregnancy, the breasts are sufficiently developed to produce milk (although it is also possible to induce lactation as described in a later section).

During the latter part of pregnancy, the woman's breasts enter into the Lactogenesis I stage, where the breasts are making colostrum (a thick, sometimes yellowish fluid), but high levels of progesterone inhibit most milk secretion and keep the volume “turned down”. It is considered medically normal for a pregnant woman to leak colostrum before her baby's birth, and also normal not to leak at all. Neither situation is an indicator of future milk production levels in the mother.

At birth, the delivery of the placenta results in a sudden drop in progesterone/estrogen/HPL levels. This abrupt withdrawal of progesterone in the presence of high prolactin levels cues Lactogenesis II (copious milk production).

Prolactin blood levels rise when the breast is stimulated, and peak around 45 minutes later. The return to pre-breastfeeding levels about three hours afterward. The release of prolactin triggers the cells in the alveoli to create milk. Some research (Cregan 2002) indicates that prolactin in milk is higher at times of higher milk production, and that the highest levels tend to occur between 2 a.m. and 6 a.m.

Other hormones (insulin, thyroxine, cortisol) are also involved, but their roles are not yet well understood. Although biochemical markers indicate that Lactogenesis II commences approximately 30-40 hours after birth, mothers do not typically begin feeling increased breast fullness (the sensation of milk "coming in") until 50-73 hours (2-3 days) after birth.

The colostrum is the first milk the baby receives; it contains higher amounts of white blood cells and antibodies than mature milk, and is especially high in immunoglobulin A (IgA), which coats the lining of babies' immature intestines, helping to prevent germs from invading baby's system. Secretory IgA also works to help prevent food allergies. (Sears, MD, William; Sears, RN, Martha: The Breastfeeding Book,Little, Brown, 2002. ISBN 0316779245)

After a baby has been nursing for 3-4 days, the colostrum in the breast slowly begins the process of changing into mature breast milk over the next two weeks. (Breastfeeding Answer Book, p. 36)

During pregnancy and the first few days postpartum, milk supply is hormonally driven. This is the endocrine control system. After milk supply has been more firmly established, Lactogenesis III begins - the autocrine (or local) control system.

At this stage, milk production is made on the law of supply and demand: The more milk removed from the breast, the more milk the breast will produce. Thus milk supply is strongly influenced by how often the baby feeds and well it is able to transfer milk out of the breast. "Low supply" can often be traced to A) too infrequent feeding/pumping, B) a jaw/mouth structure or latch inhibiting baby's ability to transfer milk effectively or C) a metabolic or digestive inability in the infant, rendering it unable to utilise the milk it receives.

Research on mothers who express their milk (Hopkinson 1988; deCarvalho 1985) indicate that for most women the more times per day a mother expresses her milk, the more milk she produces. Ongoing research (Daly 1993) shows that more fully draining the breasts also increases the rate of milk production.

The production, secretion and ejection of milk is called lactation. Most breastfeeding experts recommend at least one feeding every two to three hours to maintain the milk supply. For most women, a target of eight (8) nursing sessions/pumping sessions per 24 hours seems to keep a milk supply high not only during the early months of lactation, but especially past the fourth month. (AAP, 1997) It is not at all uncommon for newborn infants to nurse far in excess of this amount: 10 to 12 nursing sessions per 24 hours is the comparative norm, while some may even nurse 18 times in the same time frame.

The exact properties of breast milk are not entirely understood, but the nutrient content of mature milk is relatively consistent and draws its ingredients from the mother's food supply and the nutrients in her bloodstream at the time of feeding. If that supply is inadequate, content is obtained from the mother's bodily stores. (Some studies estimate that a woman burns an extra 500 calories per day simply producing milk for her offspring.) The exact composition of breast milk varies from day to day, and even hour to hour, depending on both the manner in which the baby nurses and mom's food consumption and environment, so the ratio of water to fat fluctuates. Foremilk, the milk released at the beginning of a feed, is watery, low in fat and high in carbohydrates compared with the creamier hindmilk which is released as the feed progresses. There is no sharp distinction between foremilk and hindmilk – the change is very gradual. Research from Peter Hartmann's group tells us that fat content of the milk is primarily determined by the emptiness of the breast -- the less milk in the breast, the higher the fat content. The breast can never be truly "emptied" since milk production is continuous.

Adapted from the Wikipedia article "Beginning lactation", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki