If you think your breasts finished growing when you were a teenager, think again! Many complex structures are created when you are pregnant to allow breast milk to be formed. This is a new area of research, and we are learning new information all the time. Here is a little information on how breast milk production happens during pregnancy.  

Breast Development: Before a baby is born, breasts go through changes to get ready to make milk. At puberty the breasts start to develop, and every monthly cycle from puberty until 35 a little bit of secretory (or milk producing) tissues is added. This picks up during pregnancy. We often see pregnant individuals gain a bra size during pregnancy.  

Milk-Producing Cells: Inside the breasts, there are special cells called "alveoli" that are like tiny milk factories. These cells are grouped together in clusters like branches on a tree.  

Hormones' Role: During pregnancy, hormones (like estrogen and progesterone) tell the alveoli to get ready to make milk. They help the cells grow and develop. 

Milk Production: After the baby is born, another hormone called "prolactin" tells the alveoli to start producing milk. The milk is made from the blood that’s in the mom’s body. The alveoli take nutrients from the blood and turns them into milk. 

Milk Storage: The milk travels through small tubes called "ducts" to get to the nipple. The milk is stored in the ducts until the baby needs to be fed. The “let down” reflex allows the milk to be released into the nipple.

So, in short, the breast tissue is formed and gets ready to make milk thanks to special cells and hormones, which help turn nutrients from the mom's blood into the milk that the baby drinks. 

Resources  
Hassiotou, F., & Geddes, D. (2013). Anatomy of the human mammary gland: Current status of knowledge. Clinical anatomy (New York, N.Y.), 26(1), 29–48. https://doi.org/10.1002/ca.22165  

What happens to my breasts during pregnancy. (n.d.). Medela. Retrieved July 29, 2024, from https://www.medela.com/en/breastfeeding-pumping/articles/pregnancy-preparation/what-happens-to-my-breasts-during-pregnancy