FAM Basics: Everything You Need to Know about your Endometrium

Medically reviewed by William Williams, MD

If you’re a woman, you are obviously personally familiar with the phenomenon of a period. But what exactly is your period, anyway? The blood and tissue that you see during your period actually comes from something inside of your uterus (also known as your womb), called the endometrium. But what exactly is your endometrium, and why does some of it need to exit your uterus and come out of your vagina every month as your period? What purpose does it serve while it’s still inside of your uterus?

In this latest installment of our “FAM Basics” series, we’re going to delve into exactly what the endometrium is, and why it is important for understanding female reproductive health, regardless of whether or not you are trying to get pregnant. 

What is the endometrium, and what does it have to do with your period?

At its simplest definition, the endometrium is the tissue lining the inside of your uterus, or womb. You can think of it as the “wallpaper” of the womb.

The endometrium is made up of two layers. The lower layer attaches to the smooth muscle, or myometrium, of the uterus, and serves to anchor the endometrium to the uterus. This lower layer is largely stable throughout the woman’s cycle. 

The outer layer on the other hand, also called the functional layer, changes significantly thanks to the hormonal shifts that naturally occur at different times throughout your cycle.You can think of estrogen as the grower and progesterone as the maintainer of endometrial tissue. As your estrogen level rises in the days leading up to ovulation (i.e., when one of your ovaries releases an egg), the functional layer of your endometrium thickens and gets more blood flow. This happens so that should your egg become fertilized by sperm (resulting in a newly conceived embryo), your womb is prepared for the embryo to successfully implant within the endometrial lining of your uterus. Regardless of whether or not you conceive that cycle, after ovulation, rising progesterone levels maintain and further thicken the endometrium. If you do conceive, these heightened progesterone levels stay elevated to support the embryo’s implantation, and the eventual formation of the placenta. 

If you don’t conceive that cycle (i.e., if ovulation comes and goes without the egg becoming fertilized and then implanting within the endometrium), the blood flow to the functional layer of the endometrium gradually decreases as progesterone levels naturally drop towards the end of the cycle. This results in the shedding of the endometrium you know as your period, approximately fourteen days after ovulation occurred (note that “fourteen days” is merely an average, with that number varying for different women). 

Why should you care about your endometrium if you’re not trying to get pregnant? 

It might sound from the above description of the endometrium’s functioning that it’s only important if you’re trying to become pregnant. However, good endometrial health is indicative of good reproductive health, which has implications for your overall health, too. 

That is why fertility awareness methods (FAMs), which allow women to track and observe the health and regularity of their menstrual cycles (of which the endometrium is obviously an integral part!), are just as valuable as a health tool as they are a family planning tool. Even if you are learning a FAM for health monitoring rather than for pregnancy achievement or avoidance, you still have good reason to learn about the endometrium. 

We’ll now talk about some concrete examples of where a good understanding of your endometrium can benefit your health and fertility as a woman. 


Endometriosis, a medical condition that can cause severe pain and lead to infertility, is among the most common reproductive health issues. It is an inflammatory medical condition that develops when endometrial-type tissue grows outside of the uterus in places where it doesn’t belong, such as on your ovaries or fallopian tubes, on the outside of your uterus, on your pelvis, and even on your bladder or bowel. 

Though it’s growing in the wrong places, the endometrial-type tissue is triggered to break down and shed by the same hormonal shifts that cause the breakdown and shedding of your endometrium (menstruation). However, because this tissue isn’t inside the uterus and therefore isn’t expelled in the same way as your period, it instead forms painful, thick scar tissue and adhesions (the tissue adheres to or sticks to the sides of whatever organs on which it’s growing) and can even bind pelvic organs to each other. 

For this reason, the most common symptom of endometriosis is pain, and that pain is often most severe during menstruation and/or ovulation. There’s a known association between endometriosis and infertility, though why the two are connected isn’t well understood. (Read more about diagnosis and stages of endometriosis here).

Though the birth control pill is commonly prescribed to help alleviate endometriosis symptoms by stopping cyclical menstruation, in reality, the synthetic hormones in the pill are putting a Band-Aid over the problem. In fact, hormonal birth control may even worsen endometriosis in the long run, perhaps by putting a Band-Aid over symptoms that delays actual diagnosis and surgical or other treatment. And it comes with its own set of side effects. Fortunately, if you have endometriosis, you have treatment options other than the Pill. Read more about how FAMs can help with endometriosis here, here, and here

The postpartum period and the endometrium

Did you know that what looks like postpartum “bleeding” is actually made up of lots more than just blood? During pregnancy, the endometrium has substantially thickened, and accumulated a significant placental lining as well as large amounts of blood and mucus. While the placenta is delivered along with the baby, whether vaginally or via Cesarean section, all the rest of these pregnancy “support materials” are shed over the course of the first four to six weeks after delivery (postpartum). That collective shedding and discharge is known as lochia

While many women have been told that increased activity in those first few weeks postpartum isn’t recommended because it “makes the bleeding worse,” far fewer know that the body is specifically healing from an open wound in the endometrium caused naturally by the detachment of the placenta. In fact, that wound can be as wide across as a dinner plate! Resting and minimizing activity in those first few weeks after delivery aren’t signs of weakness, they’re signs that women understand their very real need for inner and outer physical healing. 

Birth control and the endometrium

Hormonal birth control directly impacts the endometrium, keeping the functional layer artificially thinner than it would be in a naturally cycling woman. This is why hormonal birth control is often prescribed for painful and/or heavy periods. 

This function of hormonal birth control is also why it is sometimes referred to as “abortifacient,” as it would cause the death of a newly conceived embryo by making the womb an inhospitable environment for it to implant and continue growing. (Note, however, that this would require breakthrough ovulation to first occur, and it is debated how often a woman on hormonal birth control ovulates, given that the primary mechanism of action of hormonal birth control is to prevent ovulation.)

Though hormonal birth control is routinely prescribed to alleviate the symptoms of painful periods, to “regulate” irregular cycles, or for a host of other reasons, many women are unaware of how it actually works in the body. Understanding the importance of endometrial health and how birth control functions can help women make more informed family planning decisions. 

Abortion pill reversal and the endometrium

Understanding your endometrium can also help you understand your options when it comes to abortion pill reversal

When a woman opts for a medication abortion, she is prescribed two pills. The first is Mifepristone, and the second is Misoprostol. Mifepristone, also known as RU-486, works by thinning out the endometrium in order to prevent a newly conceived embryo from successfully implanting (or a successfully implanted embryo/fetus from remaining implanted) in the uterine wall. 24-48 hours after ingesting Mifepristone, the woman takes Misoprostol to induce contractions and labor which will expel the dead or dying embryo or fetus. 

If a woman changes her mind about having an abortion after taking Mifepristone but before taking Misoprostol, sometimes she can save the baby’s life by countering the Mifepristone’s effects with high doses of the endometrium-thickening hormone progesterone. 

The abortion pill reversal protocol has been successfully used to save thousands of pregnancies, simply by taking advantage of what science and medicine have discovered about  the importance of progesterone in proper endometrial functioning. Read more about it here.

More FAM Basics

If you’re interested in learning more about your fertility and reproductive health, you can check out the other installments of our FAM Basics series, where we are breaking down the elements of fertility awareness at their most basic level. And if you’re serious about taking charge of your health and fertility, consider learning a FAM from a trained instructor. Find out more about the various methods and how to find an instructor trained in the FAM of your choice, here

Additional Reading:

FAM Basics: Basal Body Temperature (BBT)

FAM Basics: What is Cervical Mucus?

4 Reasons It’s Worth It to Get a Fertility Awareness Instructor


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