The process of lactation

(This article is also available in an audio format)

By Hettie Grove – Registered nurse and advanced midwife, SACPE, ICCE, SACLC, SACLC course developer, IBCLC

The process of lactation actually starts in the foetal period of the mother as a baby.

Let’s look at normal breast development and the timeline of breast development.

Not only is breast development part of reproduction but unlike any other mammal the only mammal female who develops full breasts before they need to feed their young. Throughout a woman’s life breast development happens in a distinct rhythm from before birth right through to menopause. Changes occur during each menstrual cycle and also when she reaches her menopause. Breast development is all but static.

It all begins in the foetus when a thickening in the chest area is developed which we call the mammary ridge or milk line. At birth nipples and beginning of milk ducts are already formed. During the lifespan changes occur, and lobes or small subdivisions of breast tissue develop first. Thereafter mammary glands develop and consist of 15 to 24 lobes. From puberty these mammary glands are influenced by hormones. Involution or shrinkage of milk ducts is the final major change and around the age of 35 the mammary glands start shrinking again.

When ovulation and menstruation start, the maturing of the breasts begin with the formation of secretory glands and the end of milk ducts. The rate at which the breasts grow is different for each person.

Breast developmental stages
Stage 1 After birth till puberty we find that the tip of the nipple is raised
Stage 2 Buds appear, breast and nipples raised, and the areola, that is the darker are around the nipple, enlarges
Stage 3 Breasts become slightly larger with glandular breast tissue present
Stage 4 The areola and nipple become bigger and form a second mound above the rest of the breast
Stage 5 In adulthood the breast becomes rounded and only the nipple is raised

What happens in the menstrual cycle?

Menstrual cycles are usually cyclic. Each month during these cycles women experience fluctuations in hormones. The first half of the cycle is predominantly oestrogen which stimulates the growth of milk ducts and this gives the chance for the hormone progesterone to take over the second half of the cycle which stimulates the formation of milk glands. We believe this is responsible for cyclical changes like swelling, pain and tenderness that women experience just before menstruation. Menstruation heralded changes in breast texture therefore they have more lumpiness. The milk glands are therefore preparing for a pregnancy. The moment when pregnancy doesn’t occur the breasts return to normal.

If pregnancy occurs the breasts continue to mature and rapid growth of milk and alveolar buds take place. Breast changes is one of the very first signs or changes that heralds a pregnancy. Women start saying their breasts feel tender because the internal mammary artery runs down the side of each breast and this supplies blood to the breasts.

Due to this increased blood supply women might experience a tingling or even pricking sensation around their nipples. A bra with seams as well as lacy cups might increase the sensitivity of breasts. Breasts might also tingle with temperature changes and milk producing cells are reproducing quickly. In subsequent pregnancies some of the previous cells will still be there but a new batch will also form. The ones there from the previous pregnancy are the reason why some women might have more milk second time around (the so called muscle memory phenomenon).

Pregnancy rebuilds your breasts and actually armours them through changing the cells and proteins around them. The placental lactogens which are special hormones talk to the breasts and informs them about the sex of your baby (awesome hey!).

As the pregnancy progresses the nipples become more distinct and the areola, the area of skin around the nipple, starts to darken due to the increase in natural pigmentation, but is believed to become the bull’s eye for the baby to find the nipple more easily after birth. The combined and continued action of the hormones now oestrogen, progesterone and human placental lactogens are responsible for the growth of the glandular tissue and the milk ducts which start to swell in preparation for lactation.

In early pregnancy, breast growth is the most obvious sign of pregnancy, and some women can gain up to 680 grams in each breast (other much less). The pregnancy hormones and growing placenta encourages fat and breast ducts to grow. Breast tissue can also be found in the armpit and women with accessory breast tissue might also find that this gets larger. The alveoli which are small little sacs, almost like a grapelike form, which is where milk is secreted and stored, starts to expand and starts forming lobules which look like a bunch of grapes.

From around as early as eight weeks lots of blood vessels may be more visible just under the skin which is distinctive and known as “marbling”, all due to the increased blood supply. This network of blue veins are more obvious in fair skinned women and might not be noticeable in darker skin or in women with a higher body mass index.

The Montgomery tubercles start to appear, the little bump like formations, which are hypertrophic sebaceous glands, secrete an oil that helps to keep the skin supple and discourages bacteria forming. Each breast may have between 4 and 28 of these tubercles, which is a tell-tale and most reliable sign of a first pregnancy, but since they don’t shrink completely after birth might not be used as a diagnostic sign in subsequent pregnancies.

Soon after the ninth week of pregnancy the areola darkens more, may enlarge in diameter and become more erectile. Here the darker skin women might see more noticeable changes.

Girls who have so called inverted nipples might start to worry about how this might influence their ability to breastfeed. The largest percentage of inverted nipples will correct themselves but even if they stay inverted you will still be able to successfully breastfeed with correct positioning and help.

In first pregnancies it’s quite common for the nipple not to protrude fully. In about a third of women they will experience a degree of inversion. This improves as the skin changes and becomes more elastic, leaving about a tenth of them with some inversion at birth. Women who have breast implants might experience extreme tenderness at about 12 weeks. The skin might also feel very taut and uncomfortable.

Glandular tissue changes happens around 16 weeks. The alveoli sacs are lined with special milk producing cells which are called acinar cells. Colostrum may also be expressed from now. This is a concentrated sticky nutrition dense fluid that will feed your baby for a few days initially after birth before the production of copious amounts of mature milk. This colostrum contains sugar, protein as well as lots of antibodies and also boosts your baby’s immunity.

Due to sudden growth and increased number of blood vessels, some women might start to experience occasional leakage of a little bit of blood from the nipples. It might also be a little blood mixed with the colostrum that sticks the nipple to the bra. Although this probably is totally normal, speak to your health care worker to make sure.

Between week 20 and 22 stretch marks might become visible particularly on the underside of the breasts. Most women will develop stretch marks due to the collagen beneath the skin that stretches to accommodate the enlargement of breast tissue. The number of stretchmarks vary and is determined by genes and age – older women would have less elasticity and so experience more stretch marks. Receptors for oestrogen and progesterone start closing down which have a protective effect against cancer.

A second period of major breast growth occurs around 22 weeks and women might notice a sudden change in size. It might be worthwhile to get new bras, bearing in mind that underwiring of bras may restrict blood supply and have a crushing effect on the developing milk ducts.

As the breasts become fuller they might become more pendulous and a little sagging might take place, again elasticity plays a large role in the sagging process. Currently there is no scientific evidence that breastfeeding causes breasts to sag. Researchers have noted that there are several factors eg. Higher BMI, higher pregnancy number, smoking and greater age as well as the larger pre-pregnancy weight that can cause the breasts to sag.

Colostrum might now leak at random times more so during sex or a bath. Don’t worry if you don’t see or experience colostrum, it is there and you are more fortunate as there is no leaking. From about 27 to 28 weeks, your breasts are sufficiently developed to be able to feed a baby and to function as milk producing glands which is called lactogenesis, but the elevated progesterone levels of the pregnancy prevents the breasts from secreting milk until a few days after the birth once the placenta is delivered. The milk ducts will also start to dilate (what an awesome process).

A lot of women might experience what is called a sweat rash. The reason for this is a higher than normal proportion of blood flowing to the skin and the mucous membranes and the blood vessels dilate to accommodate it from about 30 weeks. The nipples might also be more prominent…..You are going to feed a baby! Check with your healthcare provider as this might be a fungal or bacterial infection. Try to keep the area as dry as possible.

A creamy fluid oozes from the Montgomery’s tubercles – which you might notice. Avoid using soap as this may dry them and cause them to itch. You might also remove the sebum that is there to keep your skin supple.

When you are in the homerun in the last few weeks of pregnancy, the colostrum changes from thick and yellow to pale, nearly colourless. The breasts are now fully mature and their stem cells change or differentiate into “cancer resistant high performance dairy equipment”. This protection will remain after weaning.

Labour and birth signals a physiological chain reaction and the mode of birth plays an important role in the whole breastfeeding story. Directly after the birth of the placenta the circulating oestrogen and progesterone fall and prolactin increases. At this time nerve impulses from the uterus travel to the brain via the spinal cord and the brain signals the pituitary gland to release the hormones prolactin and oxytocin. Thinking about these two hormones we can easily say that prolactin is the menu and oxytocin is the waiter that brings the food. This stimulates your breasts to start doing what they are supposed to do – lactate.

Some women might notice no changes at all till they start to produce copious amounts of milk after day 3. Some might experience these changes more gradually or not perceptibly. Remember each women is different and it may be normal for you. You may worry about insufficient glandular tissue but studies have shown no association with breast growth and subsequent milk production. If you are worried talk to your midwife or lactation consultant.

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