Breastfeeding Hormones: Progesterone

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What is Progesterone?

Progesterone is a natural hormone present in the human body. It's an important part of the female reproductive system, and it is involved in the menstrual cycle, pregnancy, and breastfeeding.

Some of the reproductive functions of progesterone include:

  • preparing the lining of the uterus for implantation of the fertilized egg
  • maintaining a healthy pregnancy
  • preventing uterine contractions and miscarriage
  • preventing ovulation and menstruation during pregnancy
  • developing the milk-making tissue in the breasts
  • signaling the onset of milk production

Progesterone and Breastfeeding

During pregnancy, the placenta produces progesterone in high amounts. Progesterone is responsible for preparing the body to produce breast milk by stimulating the growth of the milk ducts and the milk glands inside of the breasts.

Also, along with estrogen, progesterone prevents the release of prolactin, the hormone responsible for milk production. This is why there is usually only a small amount of milk produced by the breasts during pregnancy. But, once the baby and the placenta are delivered, the levels of progesterone and estrogen quickly drop. This allows prolactin levels to rise, and milk production to begin. Although uncommon, if part of the placenta remains inside of the uterus after childbirth, then the progesterone and estrogen levels will not fall, and there will be a delay in the onset of milk production until the placenta is removed.

After childbirth, breastfeeding can cause the progesterone levels in the body to remain low. Low levels of progesterone can prevent a return in fertility. Some women may have difficultly getting pregnant again while they're breastfeeding. However, this doesn't mean that pregnancy cannot occur. It is certainly possible for a woman to become pregnant, and carry a pregnancy to full term, even if she is nursing.

What About Birth Control?

Progesterone prevents milk production during pregnancy, but once milk production has begun and a milk supply is established, the use of contraception containing progesterone should not interfere with breastfeeding. Progesterone-only, or progestin-only, types of birth control are considered safe and effective for nursing women. When started after the first 6 weeks of breastfeeding, progestin-only birth control should not have any effect on breastfeeding, the baby, or the milk supply.

Estrogen, on the other hand, will interfere with the production of breast milk. So, if possible, birth control methods that contain estrogen should be avoided. 



Lawrence, Ruth A., MD, Lawrence, Robert M., MD. Breastfeeding A Guide For The Medical Profession Seventh Edition.  Mosby. 2011.

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