Overview of the Female Hormone Progesterone

If estrogen is the superhero sex hormone in women, then progesterone is its trusty sidekick. Progesterone has many of its own important functions in your body, but it also plays a big role in balancing out the effect of estrogen, especially in the lining of your uterus.

Black and white photo of a woman holding her stomach overlaid with an illustration of pain
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Progesterone Production

Progesterone is mainly produced by a specific part of your ovary called the corpus luteum. The corpus luteum develops from the follicle that releases an egg at ovulation. After ovulation, the corpus luteum ramps up its progesterone production.

Progesterone is the dominant hormone in the second half or luteal phase of your menstrual cycle, and its role is to continue the work of estrogen in preparing the lining of your uterus for pregnancy. If the egg you released is fertilized by a sperm and you become pregnant, the corpus luteum continues to produce progesterone until about 10 weeks of pregnancy. Then, your placenta takes over. If you do not become pregnant, then your corpus luteum dissolves, your progesterone levels drop, you get your period, and a new menstrual cycle begins.

In addition to the corpus luteum and placenta, progesterone is also produced but to a lesser degree by your ovaries and your adrenal glands.

Progesterone Is Essential for a Healthy Pregnancy

 As explained above, progesterone's role in pregnancy starts even before the implantation of a fertilized egg.

Progesterone is so important to achieve and maintain a healthy pregnancy that at around 10 weeks, your placenta takes over the production of progesterone for the remainder of your pregnancy. It is thought that progesterone has anti-inflammatory activity and influence over your immune system. These functions of progesterone help to protect an early developing pregnancy from miscarriage and prevent against later pregnancy loss and preterm labor.

For some women, it may be necessary to take supplemental progesterone during pregnancy.

If you conceived with the help of assisted reproductive technology you likely did not ovulate naturally so you do not have a healthy corpus luteum to produce progesterone. Your doctor will most likely recommend some type of progesterone support either in the form of a vaginal gel or tablet or by intramuscular injection. This progesterone supplementation is typically continued until about 10-12 weeks of pregnancy.

If you have a history of preterm delivery and/or preterm premature rupture of membranes in a previous pregnancy, you may be a candidate to use intramuscular progesterone to help prevent another preterm birth. These are weekly injections of a specific type of progesterone that usually begin at 16 weeks and continue through 36 weeks of pregnancy.

Your Breasts

Progesterone plays a big role in the development of your breasts. Beginning at puberty, progesterone stimulates the growth of breast tissue.

During each luteal phase, this tissue is stimulated, but it's not until you become pregnant that progesterone completes the job of preparing your breasts for milk production and lactation. 

The cyclical increase in progesterone concentration and activity in the luteal phase of your menstrual cycle is thought to be the cause of the breast swelling, pain, and tenderness that often occurs in the luteal phase of your menstrual cycle. This breast pain or mastalgia is a common symptom of PMS.

Progesterone & Progestin: Are They the Same or Different?

Progesterone is the natural hormone that is produced by your body, primarily by the corpus luteum. Because progesterone is so rapidly cleared from the body when given orally it makes it difficult to use progesterone as a supplement, especially if it is needed only in smaller doses.

Progesterone is used in certain situations like the prevention of preterm labor or to support an early pregnancy after IVF, but it is typically given either intramuscularly or vaginally to improve absorption by your body. Occasionally micronized progesterone is given orally as part of a menopausal hormone replacement regime.

Mostly to overcome the problem with absorption, a synthetic form of progesterone was created this is what is known as a progestin. By manipulating the chemical structure of natural progesterone different synthetic progestins have been created that act on the progesterone hormone receptors in your body. Progestins are used in all hormone-containing contraceptives including:

  • Oral contraceptive pill
  • Injectable contraceptive
  • Implantable contraceptive
  • Progestin-containing IUD

Most of these synthetic progestins are derived from testosterone and depending on the type of progestin it may have more or less testosterone-like activity. For example, a third-generation progestin will have less androgenic or testosterone like action than a first-generation, making it better on acne but worse for your sex drive. 

Role In Protecting Your Endometrium

Progesterone's action on the lining of your uterus is where it really functions as estrogen's sidekick. In a normal ovulatory cycle in which you don't become pregnant, the buildup and shedding of the lining of your uterus are controlled by a balance between estrogen and progesterone. If you have a condition where you are not ovulating but have excess estrogen, which is the case in polycystic ovarian syndrome and occasionally in obesity, your doctor may suggest the use of a progestin to help protect the lining of your uterus and to treat any abnormal uterine bleeding that may result. 

Progestins are also typically used in many hormone replacement options for the management of menopause symptoms. When you are in menopause the majority of the unpleasant symptoms are caused by a lack of estrogen. Taking estrogen replacement alone will effectively treat these symptoms and protect your bone. However, if you still have your uterus you need to also use a progestin or progesterone to prevent abnormal growth of your endometrium which could ultimately lead to endometrial cancer.

Progesterone Sensitivity and Luteal Phase Mood Disturbances

Like estrogen, progesterone interacts with the chemicals in your brain to control your mood and your general sense of well being. A way that progesterone does this is via its metabolite, a compound known as allopregnanolone. Allopregnanolone works on a particular receptor in your brain called the GABA receptor. Typically it has anxiety-busting action and a calming quality similar to the actions of alcohol and other sedative drugs like the benzodiazepines. This is why you may feel sleepy or a little low energy right before your period or during the early part of pregnancy. 

But for some women, the luteal phase rise in progesterone can cause varying degrees of anxiety and agitation. A similar effect can occur with some of the synthetic progestins used in hormonal contraceptives. It is thought that this opposite reaction to the typical calming effect of progesterone is caused by a disruption in how these sensitive women process allopregnanolone.

A Word From Verywell

Progesterone and estrogen are the major sex steroids in a woman's body. They act together to prepare your body for pregnancy with each ovulatory cycle and support many of the functions that keep your body healthy. It is important to understand the role progesterone plays in your body and how it has positive effects but also potentially negative side effects. 

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