I’ve been working in lactation so long I find myself not going through the basics of how the mechanism of breastfeeding works. The process is so fascinating I thought I’d take some time to talk about what hormones drive the lactation cycle and how the delicate dance of breastfeeding gets it’s start.

We are using a 28 day cycle for this example, however it is important to note that “menstrual cycles” refer to the time between bleeds and can vary considerably from person to person and still be normal.   In this example, Cycle day 1 (CD1) is the first day of bleeding, Cycle Day 14 (CD14) is ovulation, and Cycle Day 28 (CD28) is the day before bleeding starts again. Days in between will vary, but the intervals are often similar.

One of the most important parts of breastfeeding happens in breast formation during puberty. When a preteen begins the puberty the breast buds develop. Initially breast buds can look like grapes under the skin. They typically grow for a year or more before the person’s period starts.

About the time the menstrual (or period) cycle starts the hormones take on an important role. From cycle day 1 (CD1) when the monthly bleeding begins, estrogen tells the breasts to form the important structure known as glandular tissue. Breasts aren’t just made of glandular tissue. They also have a fair amount of adipose (fat) that has a lot of influence on the size of breasts. This is why breast size doesn’t always correlate to milk production. Shape can be a better indicator, but that’s also not true for every set of breasts.

Once ovulation happens around CD14, progesterone surges while estrogen wanes and breast development regresses a smidge. Progesterone is produced by the Corpus Lutiem located on an ovary. The Corpus Lutiem is created when the egg releases from the ovary until the cycle reaches CD28 The Corpus Lutiem is reabsorbed if pregnancy doesn’t occur and this is what tells the body to shed it’s uterine lining, otherwise known as the period. The first day of bleeding is CD1 and the cycle begins again.

This pattern of hormone levels is crucial for the proper development of the glandular tissue to lay down the infrastructure the breasts will need to do their job. People who experience months or years between periods may not experience enough of the hormone cycle to develop proper glandular tissue to support breastfeeding without hormonal support or treatment.  Polycystic Ovary Syndrome (PCOS) is a common culprit, however excessive athletic training, very low weight, Anorexia Nervosa, Bulimia, Morbid Obesity and other conditions can cause problems with breast development if they occur during this development stage.

In a cycle where pregnancy begins, estrogen works to help grow additional glandular tissue in the breasts to ready them for breastfeeding.  Progesterone continues to be produced via the Corpus Lutiem which develops at the spot the egg left the ovary until the placenta has developed enough to take over progesterone production around the end of the first trimester. During pregnancy both estrogen and progesterone are present working at the same time. 

The breasts continue to grow the milk making structure until delivery. Colostrum, the thick rich nutrient milk begins production later in pregnancy. Colostrum will be produced until the placenta is detached from the wall of the uterus and the progesterone levels in the blood drop. This usually takes between 3 and 5 days and is why the thinner mature milk isn’t present at birth. Once the progesterone drops, the aveolus in the chest wall closes the gaps reducing the sodium level and creates a filter to ensure larger particles can’t get through. 

Babies are designed to wait for the mature milk to come in so adding in supplement is usually unnecessary as long as breastfeeding is following it’s normal course. 

In my next blog post I will discuss issues that can occur and what action you can take to maximize your success in breastfeeding.

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