Let's Have a Chat About Hormones

I think most of us are aware that hormones play a major role in breast milk production and supply. But I’m not sure how many women know the actual importance and effects these hormones have on our bodies throughout pregnancy and lactation. Hormones start drastically increasing once conception takes place and the changes to our breasts are often the first tell-tale sign of pregnancy. This blog will highlight which hormones effect the changes to our breasts during pregnancy and lactation. I'm not going to go into too much depth physiologically speaking as I want to try and keep this blog as reader-friendly to the general mommy population who may not have a medical/nursing background.

 Estrogen and Progesterone are the 2 main hormones that cause changes to the breasts during pregnancy. Estrogen levels increase during the pregnancy, which stimulates the milk duct system to grow and become specific for milk production. Once the baby is delivered, there is a drop in estrogen levels and the body knows that it is time to start building a milk supply.

 Progesterone levels increase during pregnancy and influence the growth of the alveoli and lobes of the breast. It is also this high level of progesterone that inhibits lactation from taking place during pregnancy. Progesterone levels drop drastically once the baby is delivered and the placenta is removed triggering the body to start making milk. If a woman has any retained placental fragments, her milk supply will suffer. This is due to the powerful inhibiting influence of progesterone on prolactin (Neifert, McDonough, & Neville, 1981).

 Another important hormone that is often overlooked is called Human Placental Lactogen. It is released in large amounts by the placenta and appears to be important in breast, nipple, and areolar growth before birth. This level also drops after delivery of the placenta and promotes the action of prolactin.

 A question that I get asked quite regularly is, “Will my milk come in?” My answer to this question is always, “Yes, it will. Give your body time to do what it is designed to do.” The reason for this, was stated in the above regarding estrogen and progesterone (endocrine control or hormone driven). Once that placenta is removed, your body knows to start working on making milk. Women who choose not to breastfeed still produce breastmilk because in the first few days after delivery, milk production is driven by the changes in hormone levels after the placenta is removed. It’s once the milk has come in (and yes, sometimes it can be delayed in coming in for varying reasons) it has to be removed effectively every 2-3 hours around the clock in order for the body to keep producing more. This shift is to ‘autocrine control’ and is milk-removal driven (Prentice et al., 1989)

 Prolactin is probably the most important hormone when it comes to breast milk production/supply. During pregnancy, a steady rise in prolactin prepares the breasts for lactation (Neville, 1983). After delivery of the placenta, progesterone levels drop and prolactin levels start to rise. Prolactin levels rise in response to the baby suckling at the breast and peak approximately 45 minutes after the feeding is over. Prolactin levels tend to be at their highest between the hours of 2am and 6am. This is generally why our sweet little daytime angel babies are serious party animals in the middle of the night. Babies biologically know that if they feed more during the night, they will help their mother’s make more milk and in turn be able to take in more calories. This nighttime feeding frenzy usually leads to fuller, heavier breasts in the morning hours. Prolactin levels are at their lowest when the breast is full. So in order to keep up with good milk production, you must regularly feed your baby and ensure good drainage of both sides. 

 A few other interesting facts about prolactin that I came across are the following:

  •   Prolactin levels rise in response to anxiety and psychological stress ( Hill, Chatterton, & Aldag, 1999)
  •  Mother’s that suffer from depression have lower serum prolactin levels (Groer, 2005b).
  • Prolactin levels drop with cigarette smoking (Baron et al., 1986) and rise with beer drinking (Mennelle & Beauchamp, 1993)

 Oxytocin is a hormone that when released during labor causes the uterus to contract. During breastfeeding, oxytocin is responsible for the milk-ejection reflex, otherwise known as the let-down reflex. It causes the smooth muscle layer surrounding the alveoli to squeeze milk into the ductal system. Some women can actually feel their milk let-down. It is often described as a rushing sensation, or pins and needles throughout the breast. Being able to feel your let-down is not an indicator one way or another of adequate milk supply. Sometimes, a let-down can happen without the presence of the baby suckling at the breast. Sometimes just hearing a baby cry, or even thinking about your little one, can cause your breasts to start leaking milk. Another thing to note is that when you are breastfeeding, you may feel your uterus contracting……and it is!! Just as oxytocin causes the uterus to contract during labor, it also causes the smooth muscle of the uterus to contract while breastfeeding especially during the first week post-partum when the uterus is shrinking back to pre-pregnancy size. This happens to be one of the many benefits of breastfeeding. If these contractions are painful, try taking an anti-inflammatory like motrin or advil approx 30 minutes before a feeding is to start or lacing a heating pad or warm blanket over your belly.

 Here are some interesting facts about milk let-down as reported by La Leche League International:

·         On average 75% of mothers have more than one let-down during a feeding. (From my own experience, the average is 2-3 let-downs per/side.

·         Women have on average 2.2 let-downs per breast at each feeding. (My experience seems to be pretty close to the research!!!)

·         The more let-downs a woman has, the more milk her baby receives

·         Babies receive on average slightly more than one ounce (35ml) of milk per let-down

·         About 30% of mother’s don’t feel any let-down occurring, and most mothers don’t feel the subsequent let-down after the first

 Another interesting fact that I have no supporting research to back is that most mothers produce more milk in their right breasts. The milk seems to flow a little faster from the right breast and the right side is usually the preferred breast for most babies. I would say that 90% of the breastfeeding women I have ever worked with made more milk on their right sides. Some have speculated that most people are right-side dominant. This didn’t hold true for myself personally as I am left-handed and always made more milk on my right side. I really have no idea why this is!!!!

 So there you have it!! All you ever wanted to know about hormones and breastfeeding! I hope you have found this blog post interesting and informative. Please feel free to comment or contact me at anytime with additional questions or concerns.

Happy Breastfeeding!!!


Leanne Rzepa RN BN IBCLC

Posted on November 15, 2015 .