Progesterone is a female hormone produced by the ovaries. Along with estrogen, progesterone prepares the uterus for pregnancy and supports the fertilized egg if conception occurs. It also prepares the body for breastfeeding and milk production following pregnancy. During menopause, the ovaries stop producing progesterone and estrogen and women stop having a menstrual period.
Progesterone and the Menstrual Cycle
Progesterone is one of the four major hormones involved in the menstrual cycle. During the luteal phase of menstruation, which begins right after the egg is released, the ovaries secrete progesterone and estrogen. Progesterone prepares the uterus for the implantation of a fertilized egg by causing a thickening of the blood and nutrient rich endometrium that lines the uterine wall. If conception occurs, progesterone levels continue to increase and the lining of the uterus continues to thicken to support the fertilized egg. However, if conception fails to occur, progesterone levels decrease and the shedding of the endometrial lining of the uterus, or menstruation begins.
Progesterone and Pregnancy
Once pregnancy occurs, progesterone levels continue to increase to support the developing pregnancy. High levels of estrogen and progesterone during pregnancy are responsible for enlargement of the uterus during the first trimester. Progesterone, along with relaxin, also work to soften the pelvic cartilage and strengthen the pelvic ligaments needed to support the pregnant body. This results in a slight separation of the pelvic joints, which results in the characteristic "waddle" of pregnancy.
Progesterone and Milk Production
Progesterone aids in the development of the milk-secreting cells in the breasts. In response to the increase in progesterone, the breasts may enlarge two to three times their pre-pregnancy size. This increase in size causes the breast tissue to become softer and looser. As pregnancy ends, the milk secreting cells become more active and colostrum, or the first milk, is produced and secreted the first few days after delivery. Once estrogen and progesterone levels decrease after delivery, colostrum production stops, and the mother's regular milk is produced.
Progesterone and Menopause
As a woman approaches menopause, production of progesterone by the ovaries declines. Eventually, the ovaries stop producing progesterone and a woman can no longer get pregnant. As progesterone and estrogen levels decline, a woman begins to experience the common symptoms of menopause. The uterus decreases in size and the lining of the uterus thins. Body fat also begins to increase, cholesterol levels increase and thermoregulation of the body is altered, which causes hot flashes. Vaginal drying and a loss of sexual interest may also occur.
References
- Womenshealth.gov: Glossary
- Womenshealth.gov: Menopause
- The Cleveland Clinic: The Female Reproductive System
- American Pregnancy Association: Concerns Regarding Early Fetal Development
- "Mosby's Manual of Diagnostic and Laboratory Tests"; Kathleen D. Pagana, Ph.D., R.N. and Timothy J. Pagana, M.D.; 2006
- "Mosby's Guide to Physical Examination, 5th Edition" Henry M. Seidel, et al.; 2003
