Menstrual Cycle Progesterone: What's It For & What It Does

If you’ve spent any time on the Full Stop blog, you’ll have heard the word ‘progesterone’ before, so we’re breaking down everything there is to know about this hormone. Let’s take a look at what it is, its function in the body and menstrual cycle, and the signs that indicate your progesterone levels may be out of whack. Let’s go…

What is progesterone?

According to the Society for Endocrinology, progesterone is one of a group of steroid hormones called ‘progestogens’, and it’s secreted by something called the corpus luteum inside the ovary. This happens in the second half of your menstrual cycle, and it’s important for maintaining the early stages of pregnancy, among other things. 

Is progesterone different from progestin?

Ah, yes - good question! Progeste-rone is the hormone that occurs naturally in the body, while proge-stin refers to a synthetic version that’s created in a laboratory and used for a number of medical reasons, most commonly in oral contraceptives and hormone replacement therapy. It’s pretty much the same thing and has a similar function, but one already exists within the body, and the other is man-made. 

What does progesterone do?

OK, let’s get into the nitty gritty of its function. When the level of luteinizing hormone rises in the middle of your menstrual cycle, ovulation occurs, which means an egg is released from one of the ovaries. When this happens, the corpus luteum (a regular cyst that forms on the ovary every month) appears and begins to produce progesterone. This happens in order to prepare the body for pregnancy by encouraging glandular development and new blood vessels - the ideal conditions for a fertilised egg to implant. 

If the egg doesn’t implant, the corpus luteum breaks down, causing progesterone levels to dip again, which triggers your period. If a pregnancy does occur, the corpus luteum sticks around and continues to produce progesterone, which keeps blood vessels stimulated to supply the endometrium and provide nutrients to the embryo. As the placenta forms, it produces more progesterone than the corpus luteum, and this level remains constant throughout pregnancy. Along with its many other functions in the body, progesterone also helps to encourage the lactation process. 

What if my progesterone is too high?

If your progesterone levels are too high, it’s mostly nothing to worry about, but it is sometimes associated with a condition called congenital adrenal hyperplasia. High levels of progesterone are thought to occur because of this condition, they do not cause it. 

If you’re wondering whether or not the progestin in your hormonal birth control could cause it to rise to a dangerous level, the answer is: probably not. High levels of progestin are thought to be associated with a slightly increased risk of developing breast cancer, but there’s still a lot of research to be done in this area, so if this is something you are worried about, speak to your doctor about your concerns.  

What if it’s too low?

Progesterone is mainly important if you are trying for or having a baby, so if your progesterone levels are too low you may encounter fertility issues, or issues with your pregnancy, but your doctor will monitor this to make sure everything is as it should be. If you aren’t pregnant or trying, there are other (mostly harmless) symptoms you may want to get checked out. These include headaches or migraines, mood changes like anxiety and depression, an irregular menstrual cycle or abnormal bleeding. 

If progesterone is too low, estrogen can sometimes become the primary hormone, which can lead to symptoms like weight gain, mood swings, low libido, depression, an irregular cycle or heavy bleeding, breast tenderness, fibroids, and gallbladder issues, so keep track of any symptoms your doctor may need to know of so they can decipher what the issue may be. 

Why does my doctor want to test my progesterone levels?

There are a few reasons your doctor may want to test your progesterone levels. This could be to find out why you are experiencing fertility issues, why you may have abnormal bleeding, to diagnose an adrenal disorder, or something else. Overall, testing your hormones just makes sure they’re doing what they’re supposed to do each month.

What are the signs that progestin is causing a problem?

If you’re taking birth control or another medication that contains progestin, you can keep an eye out for side effects that include headaches, breast tenderness, tummy issues, appetite changes, weight gain, fatigue, muscle pain, mood swings, anxiety, discharge, and more. 

It’s also important to check for more serious symptoms that need attention, such as any changes in the breasts, migraines or dizziness, changes in speech, coordination or ability to swallow, weak limbs or leg swelling, shaky hands or seizures, breathlessness, a racing heartbeat or chest pain, coughing up blood, blurred vision or eye changes, unexpected vaginal bleeding, stomach pain, skin rashes, and any unidentifiable swelling. 

This list may seem exhaustive, but many of these symptoms can indicate a problem that needs medical attention sooner rather than later, so speak to your GP or call 111 if in doubt. 

Got a question about progesterone? We’re all ears! Ask away over in our Full Stop FB group, or reach out to us directly on Instagram at @itsyoppie. Don't forget that our personalised menstrual cycle subscription box can get organic tampons, PMS supplements and much more delivered easily and regularly through your letterbox, so that's one less thing you'll need to keep an eye on.