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Disclaimer: The information in this post is for educational purposes only. I am not a doctor. It is not intended to be a substitute for professional medical advice. None of the opinions are meant to diagnose or treat any disease or illness. You should always consult your healthcare provider.

Changes in Breast Milk During Pregnancy: Production & Composition

Breast milk production is controlled by hormones during pregnancy – rather than supply & demand – regardless of whether or not you are already nursing a little one when you become pregnant. This hormonal influence is what is responsible for changes in the production and composition of breast milk during pregnancy, and what makes nursing while pregnant different than nursing in other stages of life.

Changes in Breast Milk During Pregnancy Production & CompositionThe Influence of Progesterone

Progesterone and estrogen are some of the hormones that increase to sustain a pregnancy and help the developing baby grow. However, an increase in these hormones also suppresses milk secretion.

Some women find that their milk supply diminishes as pregnancy advances. It may continue to decrease even if the nursing child increases his frequency and duration at the breast. Some little ones will wean themselves without the milk supply they are accustomed to, but some are happy to continue nursing for comfort and whatever milk is produced. Older children may be able to articulate that the flavor of breastmilk changes during this time as it becomes less sweet and more salty (due to a decrease in lactose and increase in sodium).

Pregnancy hormones also sometimes cause nipple tenderness, which might make breastfeeding painful or less appealing.

Colostrum Production & Composition

Somewhere between the 4th and 8th month of pregnancy, the hormone Prolactin increases and stimulates colostrum production. Some women may begin leaking colostrum even if they are first-time moms. However, progesterone continues to keep secretion at bay for most women.

Colostrum contains many of the same components as mature human milk, but it is higher in protein and rich in antioxidents and immunoglobulins. It is usually not produced in the same quantity as mature milk, and the transition between colostrum and mature milk is gradual, with a full transition taking 3-5 days.

An older baby may notice the transition to colostrum in his pregnant mother’s milk and will sometimes wean at that time. If the older child continues to nurse and enjoy the colostrum, there is no need to worry that he is taking colostrum intended for the new baby. Breasts will continue to make colostrum until after the birth of your new little one.

Birth and the Prolactin Surge

Birth and the delivery of the placenta triggers a sudden drop in progesterone and estrogen levels, which allows prolactin to take over and begin signaling the body to make breast milk. Colostrum continues to be produced for 2-4 days then transitions to milk.

The volume of colostrum or breast milk produced varies widely between women. In general, most women pregnant for the first time don’t experience fullness in their breasts until a few days after birth when the mature milk begins coming in.

Babies who have previously weaned during pregnancy may re-establish the nursing relationship, or increase nursing frequency, after baby arrives. Nursing two or more babies of different ages is called Tandem Nursing and is a normal practice among mothers of young children around the world.

After breast milk production is established, it is no longer controlled by hormones. Instead, the removal of milk from the breasts stimulates more milk production and mothers will generally make the amount of milk sufficient for baby (and sibling) – this is called “supply & demand.” After the first few days of colostrum there’s no need to limit the amount of time an older sibling stays at the breast with baby as your body will create enough milk for both of them under healthy conditions.


Have you experienced any of these changes to breast milk during pregnancy?

Photo Credit: alberth2

Anjanette Barr is wife to a librarian and mom of four living in Juneau, Alaska and loving the life God has blessed her with. Her days are filled with lots of silly antics and laughter, mountains of laundry, and more love than she could ever hope for or deserve. She blogs at Find her also on FacebookTwitter, and Pinterest.


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