Progesterone: The Pregnancy Hormone
Now that we have covered the two big hitters, oxytocin & prolactin, we get to dive a little bit deeper. Progesterone is not commonly talked about, however, it still plays a role in the lactation process. Before we dive into progesterone, it would be helpful to discuss lactogenesis.
There are 3 stages to lactogenesis, which are simply referred to as Lactogenesis I, II, & III. Lact I actually takes place while the mother is pregnant. Typically, Lact I begins around the 16th week of pregnancy and continues until the placenta is delivered. Lact II begins as our milk begins to transition from colostrum to mature milk, which typically occurs around day 2-3 after delivery. Our bodies transition to Lact III at about 7-9 days postpartum, which is when our bodies stop relying heavily on hormones to drive our milk supply and rather transitions to a supply & demand. We remain in Lact III until we wean completely. (1)
For most of our discussions, so far this month we have been referring heavily on Lact II & III. Although, oxytocin is present in all stages, prolactin does not release until Lact I & II. This is because in Lact I, progesterone is the driving hormone. Progesterone levels by the end of pregnancy can be as high as 10x that of a non-pregnant woman. As progesterone continues to increase drastically, it is affecting many things, but one thing it is preparing our bodies for lactation (2).
Figure 1: Hormone Levels versus Trimesters through a Human Pregnancy (2)
In Lactogenesis I, progesterone begins to prepare our breasts by encouraging breast growth. We will find our milk ducts increasing in numbers and size. In fact, with each subsequent pregnancy our breasts will grow and the the quantity of milk ducts will increase. It is important that progesterone prepares our bodies for lactation in pregnancy, so that milk is readily available upon delivery. Alongside growth on the interior of our breasts, progesterone also causes our areolas to become larger and darker. This will be helpful for our newborn to be able to easily locate their food source - keeping in mind, a newborns vision is very limited. Finally, progesterone is also responsible for secretion of oils through Montgomery glands, which will lubricate our nipple. Progesterone is preparing our breast and nipples for optimal breastfeeding.
Although, physical changes are not the only thing that progesterone causes. As we hit around the 16th week of pregnancy, our bodies do begin to produce milk. However, this is not the milk, which we all think of when we refer to breastmilk - that is typically mature milk. The milk produced during pregnancy is colostrum. Often gold in color, but sometimes almost even clear and almost always thick and sticky. This milk is perfectly designed for our newborn babies. Although, it is not required, it is highly recommended that we can begin to express this milk after 36+ weeks of pregnancy. The quantity of colostrum prior to birth is not an indicator to the amount of milk we will produce of mature milk, however, expressing colostrum does highly increase one’s overall success rates of breastfeeding (3). It is believed that colostrum harvesting not only will help our mature milk “come in” quicker, but it also can help mothers feel more prepared and empowered as we begin to pursue our feeding journeys. Keep in mind though, no matter how much colostrum we express our bodies will continue to make colostrum and there will be colostrum in our breasts as our newborn is birthed and ready to eat.
Lastly, progesterone does completely inhibit our body from making mature milk. Even if we harvested our colostrum several times a day, every day from 36+ weeks until birth (which is not necessary), we still would not produce mature, white breastmilk. This is because our progesterone levels are so high, which is preventing the introduction of prolactin. Our bodies will not transition to Lactogenesis II until progesterone has drastically dropped in our bodies. This is also important to remember, because our progesterone levels will not drop until the entire placenta is delivered. Sometimes lactation consultants might ask you details regarding your delivery experience if you are facing difficulties transitioning to mature milk. This is because on very rare occasions piece(s) of a placenta can be left behind and our bodies will still have high levels of progesterone, which will prevent the forward movement of the lactogenesis process (1).
So if you are pregnant or will be pregnant, recognize some of the changes that your breasts are going through. The growth, color changes, excretion, they all serve a purpose to prepare you for the next step. Are you pregnant and curious how you can best prepare yourself for a successful breastfeeding journey? Register for a Prenatal Consultation with me! We will discuss how to safely and effectively harvest colostrum, prepare for the various types of births you plan (or maybe are not be planning) to have, and all the questions in between.
As always, I am blessed that you are including me in your feeding journey. Whether through a consultation, reading this blog, a simple Instagram like, I know this is such a delicate time and you allowing me to be included in your life is an honor.
With love,
Antoinette C.
Lauwers, J., & Swisher, A. (2020). Counseling the nursing mother: A Lactation Consultant’s Guide. Jones & Bartlett Learning.
Effect of age and gender on the QTc-interval in healthy individuals and patients with Long-QT syndrome - Scientific Figure on ResearchGate. Available from: https://www.researchgate.net/figure/Estrogen-and-progesterone-levels-during-pregnancy-and-after-parturition_fig4_318896767 [accessed 17 Sept 2024]
Lucy H. Ablett, Heather Hopper, Stephanie Maslin, How to promote exclusive breastfeeding with antenatal milk expression and implementation science: A mixed methods systematic review, Health Sciences Review, Volume 9, 2023, 100124, ISSN 2772-6320, https://doi.org/10.1016/j.hsr.2023.100124.(https://www.sciencedirect.com/science/article/pii/S2772632023000508)