The Science of Breastfeeding: How Moms’ Bodies Make Milk

If you feel like your body has morphed into one giant mystery through the pregnancy and birthing process, you are not alone. However, the surprises don’t stop there! Post labor and delivery, your body continues to respond to the beautiful journey of motherhood throughout your time breastfeeding. With all of these significant physical changes, we understand the confusion and uneasiness surrounding breastfeeding. We are here to break down some of the science behind this motherhood milestone so breastfeeding moms can understand how and why their bodies are changing. 

Changes During Pregnancy

Believe it or not, women’s bodies prepare to make breast milk months before the baby is even born. Sore breasts are one of the first signs that indicate a woman may be pregnant as they grow and prepare for milk production. When a new mom gets pregnant, hormones are released which cause milk ducts and alveoli, or clusters of cells that produce milk, to grow in order to produce breast milk.

Hormones like estrogen and progesterone are released by the placenta throughout pregnancy to ensure adequate amounts of breast milk for your little one after delivery. Additionally, these hormones are carefully measured and released by your brain so you don’t make too much milk before your baby arrives. Colostrum, the first milk your baby feeds on after birth, is created in the second trimester of pregnancy so your little one can feed right after delivery.

Breast Milk After Delivery

After the delivery of the baby and the placenta, moms’ bodies naturally make more milk to ensure their hungry newborn has enough to eat. The hormones that help increase the number of milk ducts during pregnancy, estrogen and progesterone, decrease once your baby is born, and this signals to your body that it’s time to ramp up the milk supply. 

Prolactin is the hormone that increases your milk supply to make sure your newborn has adequate nutrition for growth. During each feeding, moms’ bodies release prolactin, which gradually increases available breast milk as your baby’s appetite grows. New moms should breastfeed or pump soon after delivery and then express milk regularly so the prolactin continually increases milk supply.

Oxytocin and Breastfeeding

Commonly known as the love hormone, oxytocin does much more than encourage bonding between you and your little one–it is essential for breastfeeding. Oxytocin is the hormone that prompts your milk to leave the alveoli and travel through the milk ducts to your baby’s mouth. This process is called letdown, and there are many physical clues that can tell moms’ bodies that their baby is ready to eat. 

When you first start breastfeeding, your little one usually feeds or suckles at your breast to trigger your brain to release oxytocin and let down your milk. It can be difficult to prompt letdown when new moms are still trying to get the hang of breastfeeding, but there are a few tips and tricks to get oxytocin–and breast milk– flowing. 

For starters, relaxing can encourage letdown, though we know that’s easier said than done. If moms can find a quiet place to take some deep breaths, place a warm compress on their chest, or massage their breasts before feeding, they may find that letdown comes more quickly. As time goes on, letdown can occur more easily and sometimes unexpectedly, such as when moms hear another baby cry or when they see or think of their baby.

Although breastfeeding may be more of a scientific process than a mystical superpower, breastfeeding moms are still superheroes to us.


Your body’s process of making breast milk may be complicated, but getting your breast pump doesn’t have to be! Pumps for Mom is here to make it as easy as possible for new moms to get a free breast pump through health insurance. All you have to do is fill out our easy qualification form, and you can immediately browse top breast pump brands that may be covered by your insurance like Medela, Spectra, Ameda, Freemie, and Lansinoh. With over 15 years of experience getting new moms the best breast pump for them, the passionate team at Pumps for Mom is here to help you through every step of your breastfeeding journey. Get in touch with us and order your breast pump today!