- The Facts About Female Hormones
- 10 warning signs you may have a hormonal imbalance (and what to do about it)
- 9 Causes of Estrogen Dominance and What to Do About It
- When Estrogen Becomes a Problem
- Health Risks Associated with Estrogen Dominance
- Causes of Estrogen Dominance
- How to Clear Your Body of Excess Estrogens
- Article Sources
- Download Clue to track your period and menstrual cycle.
- Top things to know
- ## An overview:
- Act 1: The first part of the cycle
- Interlude: Ovulation
- Act 2: The second part of the cycle
- The Menstrual Cycle
- The Hypothalamus and the Pituitary
- The Ovary
- The Luteal Phase
- The Uterus
- You and Your Hormones
- Alternative names for premenstrual syndrome
- What is premenstrual syndrome?
- The monthly menstrual cycle
- What causes premenstrual syndrome?
- What are the signs and symptoms of premenstrual syndrome?
- How common is premenstrual syndrome?
- Is premenstrual syndrome inherited?
- How is premenstrual syndrome diagnosed?
- How is premenstrual syndrome treated?
- Are there any side-effects to the treatment?
- What are the longer-term implications of premenstrual syndrome?
- Are there patient support groups for people with premenstrual syndrome?
- Estrogen and the Menstrual Cycle in Humans
The Facts About Female Hormones
Hormones are specialized chemicals produced by your endocrine system that help control just about every function of your body, including growth, metabolism, and reproduction.
In women, female hormones are key components of reproduction, sexuality, and overall health and well-being.
Because female hormones play such major roles in women’s bodies, women can sometimes feel as though their hormones are controlling them.
But if you have a good understanding of the role female hormones play, you will be better equipped to recognize abnormal hormonal imbalances and deal with the natural decline in female hormones that occurs with age.
Here’s a quick rundown — your ovaries, the organs that release an egg during ovulation, produce female hormones; the two main hormones are estrogen and progesterone.
The levels of both estrogen and progesterone drop off pretty dramatically after a woman stops ovulating at menopause, but the decline in estrogen is what’s responsible for most classic menopause symptoms.
Estrogen: The Hormone Behind Your Period
Estrogen is the female hormone that fluctuates over the course of a woman’s menstrual cycle. A gradual rise in the level of estrogen in the first two weeks of the menstrual cycle — called the follicular phase of the cycle — is what causes women to build up a uterine lining each month in preparation for pregnancy, and a drop in estrogen (and progesterone) is what causes women to have a menstrual period each month.
Estrogen is also an important factor in maintaining women’s bone and cardiovascular health.
Girls begin producing estrogen at puberty, and estrogen production declines as a woman ages, until she isn’t making enough to thicken the uterine lining and have menstrual periods. In addition to the end of menstruation, some signs of low estrogen levels are hot flashes and vaginal dryness.
Some women take estrogen hormone replacement therapy (HRT) around menopause or when there is another reason for estrogen decline (such as surgical removal of the ovaries). HRT can reduce symptoms of low estrogen levels and help slow age-related bone loss in women, but there are some health risks associated with taking HRT, such as increased risk for cancer. Ask your doctor about the risks and benefits of HRT for your specific situation.
Progesterone: Essential for Pregnancy
During a woman’s childbearing years, progesterone levels rise during the second half of her menstrual cycle, after the monthly egg is released from her ovary. If she becomes pregnant, the progesterone level continues to rise, and helps keep the uterine lining thick for the developing baby. If she does not become pregnant, levels of progesterone fall, signaling the body to shed the uterine lining during menstruation.
If you have not had your uterus surgically removed (hysterectomy) and you have HRT, your doctor will likely recommend that you take progesterone in addition to estrogen to keep your uterine lining from growing too thick and to decrease your risk of endometrial cancer.
Progesterone, though essential for reproduction, sometimes produces annoying symptoms for women during the last two weeks before her menstrual period. These symptoms include bloating, breast tenderness, and acne. Sometimes a combination of physical symptoms and changes in mood regularly occur in the week before menstruation; this is often referred to as premenstrual syndrome, or PMS. PMS can often be managed by lifestyle changes — like exercising and eating a healthy diet — and over-the-counter medications, such as Motrin, Advil, or Midol Cramp (ibuprofen) and Aleve (naproxen).
Testosterone: It’s Not Just for Men
Another hormone, testosterone, is produced in low amounts in women, but is generally considered a male hormone. Elevated levels of testosterone may cause virilizing symptoms — meaning that some male physical characteristics may occur, such as abnormal, male hair growth patterns.
If your testosterone levels are abnormally high, it could be a sign of a health condition such as:
- Polycystic ovary syndrome (PCOS)
- Ovarian tumor
- Tumor on your adrenal gland
- Congenital adrenocortical hyperplasia
Too little testosterone can cause symptoms, as well. There is some evidence that declining levels of testosterone in older women and in women who have had their ovaries removed may be associated with declining sexual desire. One study showed that women who received testosterone therapy had improved sexual function, but there are still some questions about its safety and effectiveness.
Are You hCG Positive?
The hormone known as human chorionic gonadotropin, or hCG, is produced by the placenta of pregnant women. In fact, hCG is the hormone that is detected by a pregnancy test to confirm a pregnancy. During early pregnancy, hCG helps maintain the corpus luteum, which is the part of the ovary that produces progesterone after an egg is released. Levels of hCG increase until a woman is about 10 weeks pregnant, then they slowly decline throughout the rest of pregnancy. hCG is usually only produced by pregnant women, but it may also be produced by people who have certain health conditions, like germ cell tumors and trophoblastic disease, a rare disorder in which tumors grow in the cells that otherwise would grow in the placenta.
If you have concerns about your hormone levels, talk with your doctor. In some cases, your doctor may recommend a simple blood test to determine if your hormones are out of whack. Or she may refer you to an endocrinologist, a doctor who specializes in diagnosing and managing disorders that involve your hormones.
10 warning signs you may have a hormonal imbalance (and what to do about it)
No-one wants to be a slave to their hormones but how do you know if they are out of sync and what can you do to restore the balance?
Hormonal imbalances may be to blame for a range of unwanted symptoms from fatigue or weight gain to itchy skin or low mood.
Hormones are chemicals produced by glands in the endocrine system and released into the bloodstream. An imbalance occurs when there is too much or too little of a hormone.
Your hormones are important for regulating many different processes in the body including appetite and metabolism, sleep cycles, reproductive cycles and sexual function, body temperature and mood.
No surprise then that even the slightest imbalance may have a noticeable effect on your overall health and wellbeing.
Levels of hormones naturally fluctuate at various life stages, most noticeably during puberty and in women during the menstrual cycle, pregnancy and the menopause. They can also be affected by lifestyle and certain medical conditions.
What is important is to notice any symptoms and get them checked out by a qualified health professional so that you receive appropriate treatment, whether that involves using medication or complementary therapies, or making lifestyle changes, to restore the balance and your good health.
Here are 10 signs of hormonal imbalance to look out for and what you can do about them:
1. Mood swings: The female sex hormone estrogen has an effect on neurotransmitters in the brain including serotonin (a chemical that boosts mood). Fluctuations in estrogen can cause premenstrual syndrome (PMS) or depressed mood during the perimenopause (the phase before periods stop completely) and the menopause.
What to do: If feeling low or anxious interferes significantly with your day-to-day life, then dietary and lifestyle changes, such as taking up exercise, drinking less alcohol and quitting smoking, herbal remedies (such as St John’s Wort) and hormone replacement therapy (HRT), if you are perimenopausal or menopausal, can all improve your mood. Keeping a symptom diary will also help you and your doctor identify if hormonal changes could be to blame.
2. Heavy or painful periods: if accompanied by other symptoms such as abdominal pain, a frequent need to urinate, lower back pain, constipation and painful intercourse, then you may have fibroids. Fibroids are non-cancerous growths that develop in or around the womb. The exact cause is unknown although they are thought to be stimulated by estrogen while having a family history may also increase your risk.
What to do: If you are suffering symptoms, consult a qualified health professional who may prescribe medication to shrink the fibroids. In severe cases or if medication does not resolve the problem, surgery may be considered to remove them.
3. Low libido: Low libido is particularly common in women going through the perimenopause or menopause due to falling levels of estrogen and testosterone (although known as a male hormone, women also have testosterone). Other menopausal symptoms such as night sweats, fatigue, low mood and anxiety can also have an impact on your sex life.
What to do: If you are going through the menopause, you may wish to consult a women’s health expert about trying testosterone as part of your HRT. This can improve your libido as well as boost your mood and energy levels. It is given at very low doses as a gel applied to the skin.
4. Insomnia and poor-quality sleep: During the perimenopause and menopause, the ovaries gradually produce less estrogen and progesterone, which promotes sleep. Falling estrogen levels may also contribute to night sweats which disrupt your sleep, contributing to fatigue and lack of energy.
What to do: The first step is to get an accurate diagnosis. If you are going through the perimenopause or menopause, discuss the benefits of HRT, which will restore levels of estrogen and progestogen, with your doctor. You can also do practical things to improve your sleep such as wear cotton night-clothes, sleep between cotton sheets, keep your bedroom cool and as dark as possible, take up exercise and reduce alcohol and caffeine intake.
5. Unexplained weight gain: A number of hormone-related conditions can cause weight gain including an underactive thyroid (when your thyroid gland does not produce enough thyroid hormones which regulate metabolism), polycystic ovary syndrome (PCOS) (a hormone-related problem causing small cysts on the ovaries) and the menopause (which results in hormonal changes that can make you more likely to gain weight around your abdomen).
What to do: If you are experiencing unexplained weight gain, with no change in diet or exercise levels, you may wish to consult an expert in women’s health to check for conditions such as thyroid problems or ovarian cysts. If you are going through the menopause, you may wish to discuss the benefits of HRT with your doctor. Some women believe HRT causes weight gain but there is no evidence to support this.
6. Skin problems: Chronic adult acne can be a sign of low levels of estrogen and progesterone and high levels of androgen hormones and can also indicate polycystic ovary syndrome. Similarly, hormonal imbalances during pregnancy or the menopause can cause itchy skin while dry skin is a symptom of the menopause or thyroid problems.
What to do: If you believe a persistent skin problem is caused by a hormonal balance, you could consult a women’s health expert to diagnose and treat the underlying problem.
7. Fertility problems: hormonal imbalance is one of the leading causes of female infertility and with changing hormone levels, a woman’s fertility naturally drops after the age of 35. High levels of follicle-stimulating hormone (FSH) can reduce a woman’s chances of getting pregnant while low levels of luteinizing hormone (LH), which stimulates the ovaries to release an egg and start producing progesterone, can also cause fertility problems. Early menopause and other hormone-related conditions such as PCOS will affect your fertility.
What to do: Your GP can arrange for a blood test to check FSH and LH levels and if you have been trying to conceive for a year, or less time if you are over 35, then you may consider seeing a women’s health expert to diagnose any underlying cause of your difficulty to conceive.
8. Headaches: Many women suffer headaches due to hormonal changes during the menstrual cycle, pregnancy or menopause.
What to do: Keeping a symptom diary will help you, and your doctor, identify the triggers of your headaches. Eating small, frequent snacks and keeping to a regular sleep pattern can help. If you have regular attacks, your doctor may prescribe anti-migraine medicines or taking the contraceptive pill or HRT may help.
9. Weak bones: Falling levels of estrogen during the perimenopause and menopause can cause bone loss.
What to do: Often women do not realise they have brittle bones until they suffer a fracture which is why it is important to adopt lifestyle changes to improve your bone health as you reach middle age and beyond. Weight-bearing exercise, such as running, tennis or dancing, a healthy diet including sources of calcium and vitamin D, and taking HRT to deal with menopause symptoms can all be beneficial.
10. Vaginal dryness: Vaginal dryness is most often caused by a fall in estrogen levels, especially during the perimenopause and menopause. Taking the contraceptive pill or antidepressants can also change hormone levels, resulting in the problem.
What to do: Practical steps can include washing with unperfumed soaps and using water-based lubricants. If your symptoms are due to the menopause, then HRT will help by increasing levels of estrogen.
Please get in touch if you would like more information about hormonal health and an appointment with one of our healthcare professionals.
9 Causes of Estrogen Dominance and What to Do About It
January 3rd, 2020
• Free eBook: 35 Gut Recovery Recipes
Are you struggling with infertility, PMS, mood swings, weight gain, or low libido? If so, you could be dealing with a hormone imbalance. Having too much estrogen—known as estrogen dominance—is not only linked to a set of frustrating and uncomfortable symptoms, it also puts you at risk for a whole host of chronic issues. From fatigue and irritability to autoimmune conditions, thyroid dysfunction, and cancer, estrogen can wreak havoc on your body if it’s not in proper balance with your other reproductive hormones, such as progesterone.
And here’s the hard truth—estrogen dominance is at an all-time high. We’re seeing the rates increase dramatically across the board, in both women and men, across age ranges. And the rates of cancers and chronic illnesses linked with an overload of estrogen are on the rise right along with it.
That’s because we are being constantly bombarded by xenoestrogens. These are industrial chemicals that mimic the behavior of estrogens. They’re everywhere in our modern environment. They’re in our food, personal care products, furniture and clothes. From the water we drink to the food we eat, we encounter a shocking number of these endocrine-disrupting xenoestrogens in the course of a day, without even knowing it.
It scares me when I think about how toxic our world has become, especially since I am the mother of a little girl. That’s why I’m even more passionate about arming you with the knowledge you need to make smart choices for yourself and your family.
In this article, I’ll walk you through what estrogen dominance is and how you’re being exposed to xenoestrogens. I’ll share simple, diet and lifestyle changes you can make to minimize your risk, naturally clear estrogen from your system, and maintain an optimal hormonal balance.
When Estrogen Becomes a Problem
You—and everyone else—naturally produces the hormone estrogen in your adrenal glands and stored fat tissue, as well as the ovaries in women and the testes in men. Estrogen is necessary for many important functions such as childbearing, keeping cholesterol in check, and protecting bone health.1 It’s when your estrogen levels get out of balance with your other hormones that it can lead to a number of issues in both men and women.
Symptoms of Estrogen Dominance
- Weight gain, mainly in hips, waist, and thighs
- Menstrual problems such as light or heavy bleeding
- Fibrocystic breasts
- Uterine fibroids
- Loss of sex drive
- Depression or anxiety
- Enlarged breasts
- Sexual dysfunction
Conventional medicine tells us that it’s your lifelong exposure and total amount of estrogens that pose a problem and cause cancer. For instance, if you started your period at a young age, or had children late in life or not at all, you would be at a higher risk. However, that’s not entirely true. It’s really your lifelong exposure to bad metabolites of estrogen that increases your cancer risk. Let me explain.
Estrogen is metabolized by the liver through three different pathways. Depending on the pathway, estrogen will be converted into good or bad metabolites. The 2-hydroxy metabolic pathway is considered good as it has the lowest risk for cancer and other problems. Meanwhile, the 16-hydroxy and 4-hydroxy pathways are considered bad and associated with higher risks of breast cancer.2 Using the 2-hydroxy pathway, your body produces good estrogen metabolites, which support healthy mood, libido, breast tissue, and reproductive health. When your body is converting too many of your hormones using the 16-hydroxy and 4-hydroxy pathways, that’s when you experience estrogen dominant symptoms such as irritability, vaginal dryness, and PMS, and are at a higher risk of developing cancer.
So it’s not about your total estrogens. It’s about your total estrogen metabolites. Nutritional status, liver health, stress, diet, and sleep all determine which metabolic pathways are used. Gene mutations such as COMT and MTHFR also impair your ability to methylate and detoxify your hormones, as do a number of environmental and lifestyle factors that I’ll describe in more detail later.
Health Risks Associated with Estrogen Dominance
By far the biggest risk associated with estrogen dominance is hormone-dependent cancer including breast cancer in both women and men, uterine and ovarian cancers in women, and prostate cancer in men.3 Breast cancer specifically is more rampant than ever. One in eight women will get breast cancer in her lifetime.4
Hormonal cancers are associated with stored fat, which produces the most potent form of estrogen, estradiol. This type of harmful estrogen is more difficult for your body to detoxify, leading to more circulating estrogen and “bad” estrogen metabolites.
In some autoimmune conditions, high levels of estrogen can enhance the inflammatory response of the immune system, increasing the antibodies that attack your body’s own tissues. However, it’s not entirely a clear-cut issue. Estrogen is actually protective for some autoimmune conditions, such as multiple sclerosis (MS). It seems to be the sharp fluctuations in estrogen levels (such as those that happen around childbirth and menopause) that contribute to autoimmunity. It also has to do with the types of estrogens in your system, and whether they are your natural hormones or the synthetic xenoestrogens that exist in our environment.
Because women tend to be more susceptible to estrogen dominance, this helps explain why autoimmune conditions are so much more common among women.5
Hashimoto’s and Thyroid Dysfunction
Excess estrogen increases levels of thyroid binding globulin (TBG) which is the protein that allows your thyroid hormones to travel through your bloodstream. When thyroid hormones are attached to TBG they remain inactive, so your thyroid hormones can’t be stored in your tissues or converted to their active form in order to fuel your body and metabolic processes. I explain this more in depth in my book, The Thyroid Connection.
Estrogen dominance also plays a factor in Candida overgrowth. Research shows that exposing Candida albicans to estrogen increases its virulence, which is why women taking birth control or traditional hormone replacement therapy tend to be more susceptible to yeast infections.6
Causes of Estrogen Dominance
Every day we are under constant attack by environmental toxins that lead to the creation of bad estrogen metabolites. Hormone-mimicking xenoestrogens combined with your own diet and lifestyle habits can all contribute to estrogen dominance.
By far one of the biggest sources of excess estrogen is our modern diet. Commercially raised animals are injected with growth hormones to make them grow bigger and faster or increase milk production. These hormones make their way into your food where they can disrupt your own natural hormone balance.
Plus, any of the pesticides, herbicides, and fungicides found on conventional produce are known endocrine disruptors that interfere with your natural hormone activity and metabolism.7 While they may only exist in small quantities on individual fruits and vegetables, the cumulative effect quickly adds up and hasn’t been studied enough to determine what the long-term effects might be.
Unfortunately, our water has become heavily polluted with hormone-disrupting compounds including pesticides and fertilizers, synthetic and natural estrogens from livestock and prescription medications, and an unknown number of industrial chemicals from chemical plant runoff or the disposal of plastics and chemicals in landfills.8
Coal-burning plants emit over 70,000 pounds of mercury in the into the air each year, which then settles into our water and impacts our hormonal levels (more on that below).
3. Personal Care Products
Cosmetics, lotions, shampoos, soaps, toothpastes, and the numerous other body products we use often contain parabens, phenoxyethanol, phthalates and other compounds that all have estrogenic activity.9 And since the average person uses 10-15 body products a day, with a total of 126 different ingredients, this exposure can quickly add up!
You’d think that beauty products would be regulated for safety. However, you’d be surprised to learn that they are regulated by an internal review board, so they’re really just regulating themselves, leading to the inclusion of all sorts of hidden endocrine disruptors in these products you use every day.
Xenoestrogens in skin care products are especially harmful because they are absorbed directly into your tissues, and so never have the chance to be detoxified through your liver.10 Be wary of deodorants or other personal care products that contain an unspecified “fragrance,” as this can be virtually anything and it tends to be a catch-all term for hidden phthalates or other hormone-disrupting chemicals.
4. Gut Dysbiosis
Your gut microbiome regulates circulating estrogen using an enzyme known as beta-glucuronidase. When your microbiome is out of balance, as in the case of Small Intestinal Bacterial Overgrowth (SIBO), these enzymes can’t properly metabolize estrogens, which leaves you more susceptible to breast cancer and other conditions caused by estrogen dominance.11
5. BPA and Other Plastics
Plastic in all its forms, including in water bottles, food wrap, and storage containers, contain hormone mimicking xenoestrogens that can leach into what you’re eating or drinking and cause major problems for your health. Even products marked “BPA-free” are not safe, and in fact contain chemicals whose effects aren’t as well-known.12
Microwaving, dishwashing, and exposing plastic to sunlight increases the estrogenic activity of plastic even more.
You may not be aware that every time you take a receipt from the store, you are dealing a blow to your hormones. Receipts printed on thermal paper are a major source of endocrine-disrupting bisphenol-A (BPA). People who handle receipts frequently have significantly elevated levels of BPA in their urine.13 And because these xenoestrogens are getting absorbed through your skin, it’s a more direct hit to your system.
6. Heavy Metals
Similar to plastics, heavy metals such as cadmium, lead, and mercury have estrogen-mimicking properties. It’s even been suggested that the presence of these endocrine-disrupting elements in our environment may be behind the earlier-onset puberty that has become the norm in our modern societies.14
7. Body Fat
Excess body fat (especially stored in the hips, waist, and thighs) is one of the leading causes of estrogen dominance.15 Not only does fat tissue absorb and store estrogen circulating in your bloodstream, it also synthesizes estrogen from your other hormones.16 Having high levels of estrogen cues your body to make more fat cells, which then produce even more estrogen, creating a vicious cycle.
8. Hormone Replacement Therapy (HRT) and Birth Control
Hormone replacement therapy medications and most oral contraceptives contain estrogen without the necessary progesterone to maintain proper hormone balance. The hormones used in both HRT and birth control also tend to be toxic, synthetic hormones that are not easily metabolized by the liver, leading to DNA damage and an increased risk for breast and endometrial cancer.17
9. Chronic Stress
When you’re chronically stressed (as so many of us are), your body begins to use the sex hormone progesterone to make cortisol.18 Low levels of progesterone lead to estrogen dominance.
How to Clear Your Body of Excess Estrogens
Now that you know what estrogen dominance is and where it comes from, what steps can you take to prevent it? Or if you suspect you may already be estrogen dominant, how can you clear your body of those excess estrogens and restore hormone balance?
Taming the toxins is a key component of The Myers Way®, and as I explain in my books and programs, I use a two-step approach to help you minimize your exposure and then clear the toxins safely from your body.
Step 1: Prevention
- Eat Clean Food: Eliminate all toxic foods from your diet that contain hidden estrogens, including conventional meat, dairy products, and produce. Opt for grass-fed, pasture-raised, and organic whenever possible to avoid added hormones, pesticides, and fertilizers used in conventional farming methods. Be sure to check out the Environmental Working Group’s Dirty Dozen list for the worst offenders if buying all organic produce isn’t feasible.
- Filter Your Water: Thanks to pollution and runoff, hormone-disruptors are rampant in our water supply. To protect your water, I recommend installing water filters on all of your taps and showerheads.
- Use Non-Toxic Body Products: Switch out chemical-laden personal care products for safer versions that are free and clear of any synthetic compounds. I get all of my non-toxic beauty products from Beautycounter.
- Ditch the Plastic: Replace all the plastic storage containers and water bottles with glass or stainless steel.
- Minimize Your Mercury Exposure: Check out this article to learn more about avoiding mercury and how to test your levels.
- Consider Hormone Alternatives: If taking HRT, consider speaking to your doctor about alternative methods that address the root causes of your menopausal symptoms. Bioidentical hormone therapy is a more natural option for those who depend on HRT for symptom relief, using hormones extracted from plants that act just like the hormones we produce in our body. The same goes for women using oral contraceptives to treat symptoms such as acne or heavy periods. Though it may help to relieve your symptoms now, it may just be throwing fuel on the fire, leading to estrogen dominance and all its associated health risks in the long run. For both HRT and birth control users, you can try my Hormone Balance Support Kit for relieving menopausal symptoms and supporting a healthy menstrual cycle.
- Relieve Your Stress: Take measures to relieve your stress, such as yoga or meditation, and make sure you’re getting adequate sleep at night to let your body detox and recover from the stresses of the day.
Step 2: Detoxification
One of the best ways to clear your body of excess estrogens and achieve proper hormone balance for both men and women is EstroProtect. EstroProtect contains a blend of natural ingredients that support optimal estrogen metabolism and detoxification.
It features Calcium-D-Glucarate, which binds estrogen that would otherwise be recycled and reabsorbed by your body and flushes it out of your system. It also includes Diindolymethane (DIM) to help you metabolize estrogen into more of its good metabolites instead of the bad. And N-Acetyl-L-Cysteine (NAC), Milk Thistle, and Alpha-Lipoic acid all support your liver as it works to safely detoxify and clear the estrogens.
Because of our constant exposure to xenoestrogens and estrogens, I recommended this supplement to all of the women I saw in my clinic, especially those who were dealing with estrogen dominance, were exposed to xenoestrogens, had a family history of hormonal cancers, or who themselves had a hormonal cancer and were in remission.
Once you’ve familiarized yourself with the main sources of estrogen and begin taking the proper lifestyle measures to avoid them in the future, you can start feeling your best again. And you can feel even better knowing you’re reducing your risk for a number of chronic illnesses!
Download Clue to track your period and menstrual cycle.
Top things to know
The menstrual cycle starts with the first day of the period and ends when the next period begins
Hormone signals are sent back and forth between the brain and the ovaries, causing changes to the sacs in the ovaries that contain eggs (follicles) and the uterus
The first part of the cycle prepares an egg to be released from the ovary and builds the lining of the uterus
The second part of the cycle prepares the uterus and body to accept a fertilized egg, or to start the next cycle if pregnancy doesn’t happen
The menstrual cycle is more than just the period. In fact, the period is just the first phase of the cycle. The menstrual cycle is actually made up of two cycles that interact and overlap—one happening in the ovaries and one in the uterus. The brain, ovaries, and uterus work together and communicate through hormones (chemical signals sent through the blood from one part of the body to another) to keep the cycle going.
A menstrual cycle starts with the first day of the period and ends with the start of the next period. An entire menstrual cycle usually lasts between 24 and 38 days (1), but the length may vary from cycle to cycle, and may also change over the years. Cycle length changes between menarche (when periods first start during puberty) and menopause (when periods stop permanently) (2,3).
Understanding the menstrual cycle is important because it can impact the body from head to toe. Some people notice changes in their hair, skin, poop, chronic disease symptoms, mental health, migraine headaches, or the way they experience sex at different points in the menstrual cycle. It’s also the body’s way of preparing for pregnancy over and over again, so people having penis-in-vagina sex (the kind of sex you can become pregnant from) may want to pay attention to the menstrual cycle. Hormonal methods of birth control prevent some or all of the steps in the cycle from happening, which keeps pregnancy from occurring.
Read on for the breakdown of each phase of the cycle and what is happening in the uterus and in the ovaries.
## An overview:
Menstruation: The period—the shedding of the uterine lining. Levels of estrogen and progesterone are low.
The follicular phase: The time between the first day of the period and ovulation. Estrogen rises as an egg prepares to be released.
The proliferative phase: After the period, the uterine lining builds back up again.
Ovulation: The release of the egg from the ovary, mid-cycle. Estrogen peaks just beforehand, and then drops shortly afterwards.
The luteal phase: The time between ovulation and before the start of menstruation, when the body prepares for a possible pregnancy. Progesterone is produced, peaks, and then drops.
The secretory phase: The uterine lining produces chemicals that will either help support an early pregnancy or will prepare the lining to break down and shed if pregnancy doesn’t occur.
Act 1: The first part of the cycle
When: From the time bleeding starts to the time it ends What: Old blood and tissue from inside the uterus is shed through the vagina
Each menstrual cycle starts with menstruation (the period). A period is the normal shedding of blood and endometrium (the lining of the uterus) through the cervix and vagina. A normal period may last up to 8 days (1), but on average lasts about 5 or 6 (4).
Ovaries: Follicular phase
When: From the start of the period until ovulation What: Signals from the brain tell the ovaries to prepare an egg that will be released
During the period, the pituitary gland (a small area at the base of the brain that makes hormones) produces a hormone called follicle stimulating hormone (FSH). FSH tells the ovaries to prepare an egg for ovulation (release of an egg from the ovary). Throughout the menstrual cycle, there are multiple follicles (fluid filled sacs containing eggs) in each ovary at different stages of development (5,6). About halfway through the follicular phase (just as the period is ending) one follicle in one of the ovaries is the largest of all the follicles at about 1 cm (0.4 in) (6,7). This follicle becomes the dominant follicle and is the one prepared to be released at ovulation. The dominant follicle produces estrogen as it grows (8), which peaks just before ovulation happens (7). For most people, the follicular phase lasts 10-22 days, but this can vary from cycle-to-cycle (4).
Uterus: Proliferative phase
When: From the end of the period until ovulation What: The uterus builds up a thick inner lining
While the ovaries are working on developing the egg-containing follicles, the uterus is responding to the estrogen produced by the follicles, rebuilding the lining that was just shed during the last period. This is called the proliferative phase because the endometrium (the lining of the uterus) becomes thicker. The endometrium is thinnest during the period, and thickens throughout this phase until ovulation occurs (9). The uterus does this to create a place where a potential fertilized egg can implant and grow (10).
When: About midway through the cycle, but this can change cycle-to-cycle. Ovulation divides the two phases of the ovarian cycle (the follicular phase and the luteal phase) What: An egg is released from the ovary into the fallopian tube
The dominant follicle in the ovary produces more and more estrogen as it grows larger. The dominant follicle reaches about 2 cm (0.8 in)—but can be up to 3 cm—at its largest right before ovulation (6,7). When estrogen levels are high enough, they signal to the brain causing a dramatic increase in luteinizing hormone (LH) (11). This spike is what causes ovulation (release of the egg from the ovary) to occur. Ovulation usually happens about 13-15 days before the start of the next period (12).
Act 2: The second part of the cycle
Ovary: Luteal Phase
When: From ovulation until the start of the next period What: The sac that contained the egg produces estrogen and progesterone
Once ovulation occurs, the follicle that contained the egg transforms into something called a corpus luteum and begins to produce progesterone as well as estrogen (10,13). Progesterone levels peak about halfway through this phase (14). The hormonal changes of the luteal phase are associated with common premenstrual symptoms that many people experience, such as mood changes, headaches, acne, bloating, and breast tenderness.
If an egg is fertilized, progesterone from the corpus luteum supports the early pregnancy (15). If no fertilization occurs, the corpus luteum will start to break down between 9 and 11 days after ovulation (10). This results in a drop in estrogen and progesterone levels, which causes menstruation. The luteal phase typically lasts about 14 days, but between 9 and 16 days is common (4,12).
Uterus: Secretory Phase
When: From ovulation until the start of the next period What: The lining of the uterus releases or secretes chemicals that will either help an early pregnancy attach if an egg was fertilized, or help the lining break down and shed if no egg was fertilized
During this phase, the endometrium prepares to either support a pregnancy or to break down for menstruation. Rising levels of progesterone cause the endometrium to stop thickening and to start preparing for the potential attachment of a fertilized egg. The secretory phase gets its name because the endometrium is secreting (producing and releasing) many types of chemical messengers. The most notable of these messengers are the prostaglandins, which are secreted by endometrial cells and cause changes to other cells nearby.
Two prostaglandins in particular called, “PGF2α” and “PGE2”, cause the uterine muscle to contract (cramp). The amounts of these prostaglandins rise after ovulation and reach their peak during menstruation (16,17). The cramping caused by this prostaglandin helps trigger the period. If a pregnancy occurs, prostaglandin production is inhibited (18) so that these contractions won’t impact an early pregnancy. If pregnancy does not occur, the corpus luteum stops producing estrogen and progesterone. The drop in hormones, along with the effects of the prostaglandins, cause the blood vessels to constrict (tighten) and tissue of the endometrium to break down (10).
Menstruation begins, and the whole cycle starts all over again.
Tracking symptoms throughout your menstrual cycle in Clue can help you feel more in control by helping you notice patterns and anticipate changes. It can also help you identify if something is out of the norm for you and seek the advice of a healthcare provider if needed.
over 115k ratings
over 115k ratings
The Menstrual Cycle
The female reproductive system is a wonderfully complex system involving continuous communication between the brain centers and the ovary. Hormones secreted by the hypothalamus, the pituitary and the ovary are the messengers that regulate the monthly cycle.
The Hypothalamus and the Pituitary
The hypothalamus is located centrally in the brain and communicates by way of an exchange of blood with the pituitary gland. Several neuroendocrine agents, or hormones, are produced by the hypothalamus. The most important hormone for reproduction is called gonadotropin releasing hormone, better known as GnRH. It is released in a rhythmic fashion every 60 to 120 minutes.
GnRH stimulates the pituitary gland to produce follicle stimulating hormone (FSH), the hormone responsible for starting follicle (egg) development and causing the level of estrogen, the primary female hormone, to rise. Leutinizing hormone (LH), the other reproductive pituitary hormone, aids in egg maturation and provides the hormonal trigger to cause ovulation and the release of eggs from the ovary.
The main function of the ovaries is the production of eggs and hormones. At birth, the ovaries contain several million immature eggs. No new eggs will be developed. These eggs are constantly undergoing a process of development and loss. Most will die without reaching maturity. This process of egg loss occurs at all times, including before birth, before puberty and while on birth control pills. The ovary undergoes a constant process of egg depletion throughout its lifetime.
As the levels of FSH and LH in the blood increase with puberty, the eggs begin to mature and a collection of fluid — the follicle — begins to develop around each one.
The first day of menses is identified as cycle day one. Estrogen is at a low point. Therefore, the pituitary secretes FSH and LH, a process which actually begins before the onset of your menses. These hormones in turn stimulate the growth of several ovarian follicles, each containing one egg. The number of follicles in the monthly “cohort” of developing follicles is unique to each individual. One follicle will soon begin to grow faster than others. This is called the dominant follicle.
As the follicle grows, blood levels of estrogen rise significantly by cycle day seven. This increase in estrogen begins to inhibit the secretion of FSH. The fall in FSH allows smaller follicles to die off. They are, in effect, “starved” of FSH.
When the level of estrogen is sufficiently high, it produces a sudden release of LH, usually around day thirteen of the cycle. This LH peak triggers a complex set of events within the follicles that result in the final maturation of the egg and follicular collapse with egg extrusion. Ovulation takes place 28 to 36 hours after the onset of the LH surge and 10 to 12 hours after LH reaches its peak.
The cells in the ovarian follicle that are left behind after ovulation undergo a transformation and become the corpus luteum. In addition to estrogen, they now produce high amounts of progesterone to prepare the lining of the uterus for implantation.
The Luteal Phase
The luteal phase, or second half of the menstrual cycle, begins with ovulation and lasts approximately 14 days — typically 12 to 15 days.
During this period, changes occur that will support the fertilized egg, which is called an embryo, should pregnancy result. The hormone responsible for these changes is progesterone, which is manufactured by the corpus luteum. Under the influence of progesterone, the uterus begins to create a highly vascularized bed for a fertilized egg.
If a pregnancy occurs, the corpus luteum produces progesterone until about 10 weeks gestation. Otherwise, if no embryo implants, the circulating levels of hormone decline with the degeneration of the corpus luteum and the shedding of the lining of the uterus (endometrium), leading to bleeding.
The lining of the uterus, or endometrium, prepares each month for the implantation of an embryo. This preparation occurs under the influence of estrogen and progesterone from the ovary. If no pregnancy develops, the endometrium is shed as a menstrual period, about fourteen days after ovulation.
You and Your Hormones
Alternative names for premenstrual syndrome
PMS; premenstrual tension; PMT; premenstrual dysphoric disorder (severe PMS)
What is premenstrual syndrome?
Woman pressing her abdomen to relieve cramps due to premenstrual syndrome.
Most women experience some symptoms in the days leading up to their monthly period (i.e. during the second half of the menstrual cycle). Each woman’s symptoms are different and can vary month to month. If these symptoms, which can manifest as physical, behavioural and psychological, recur and are severe enough to impact on the woman’s daily life they are defined as premenstrual syndrome. Symptoms usually disappear or significantly decrease by the end of menstruation. More severe PMS is known as premenstrual dysphoric disorder (PMDD).
The monthly menstrual cycle
The first day of the menstrual cycle is defined as the first day of a monthly period. Around mid-cycle – approximately day 14 if cycles are regular – ovulation occurs. The empty follicle that has nurtured the egg forms a corpus luteum, which produces high levels of progesterone and lower levels of oestradiol to prepare the womb for pregnancy if conception has occurred. If the egg is not fertilised then the corpus luteum begins to break down and the production of progesterone and oestradiol begins to fall. This starts about a week before the next period.
What causes premenstrual syndrome?
The exact cause of premenstrual syndrome is not known however hormonal changes are thought to trigger the symptoms. After ovulation, when the corpus luteum begins to break down, the decline in progesterone levels towards the end of the menstrual cycle affects various chemicals in the brain (such as serotonin). Women with premenstrual syndrome do not have abnormal levels of hormones but they appear to be more sensitive to the effects of progesterone and oestrogen.
The degree to which these processes affect a woman will be influenced by her psychological and social wellbeing at that particular time in her life.
What are the signs and symptoms of premenstrual syndrome?
Up to 150 symptoms have been identified as part of premenstrual syndrome. The most common physical symptoms include breast tenderness, feeling bloated, headaches, acne, abdominal pain and fatigue. The most commonly experienced psychological symptoms include mood swings, irritability, anxiety, depression, feeling tearful, upset/emotional and difficulty in concentrating.
How common is premenstrual syndrome?
It is difficult to estimate how many women are affected. Up to 80% of women are thought to experience premenstrual symptoms while premenstrual syndrome itself is believed to affect between 5% and 25% of women in the reproductive age group. An estimated 5% to 8% of women suffer from severe premenstrual syndrome also known as premenstrual dysphoric disorder.
Is premenstrual syndrome inherited?
Early research has suggested that there may be a genetic-predisposition to developing premenstrual syndrome; however, this has not been proven. More research is needed to clarify whether premenstrual syndrome runs in families.
How is premenstrual syndrome diagnosed?
Diagnosis of premenstrual syndrome is based on the symptoms experienced by the patient and the point during the menstrual cycle at which the symptoms are experienced. In order to make a diagnosis, women are encouraged to keep a diary of their symptoms over the course of at least two consecutive months.
How is premenstrual syndrome treated?
Because the exact cause of premenstrual syndrome is not yet understood treatment is focused on providing relief from symptoms. Management of premenstrual syndrome follows a tiered approach and each treatment option may take up to three months to make a noticeable difference. Initial management involves encouraging a woman to lead a healthy lifestyle, in terms of a balanced diet, regular exercise and minimising stress, as well as avoiding salt, caffeine and alcohol.
There are a number of herbal and vitamin supplements that are suggested for treatment of premenstrual syndrome. Some small studies have suggested that a good intake of the B vitamins thiamine and riboflavin as well as calcium and vitamin D may reduce the risk of premenstrual syndrome. Chasteberry (Vitex agnus castus) supplements are also supported by small studies. Further research is required to clarify the benefits of all of these. A woman should consult her doctor or dietician to discuss a regime that would be appropriate for her.
Cognitive behavioural therapy (a specific type of talking therapy) has also been shown to be of benefit in the management of premenstrual syndrome.
Medical treatments fall into two main groups: hormonal treatments and selective serotonin receptor inhibitors (or SSRIs).
Hormonal treatments – premenstrual syndrome can be alleviated in a proportion of women by using hormonal contraceptives that suppress ovulation. There are a number of ways to do this. The woman may be given oestrogen patches with progestogen (progesterone) in the form of tablets or a steroid-impregnated intrauterine device, called Mirena. Sometimes the combined oral contraceptive pill may be used. If a woman’s symptoms are very severe, she may be referred to a gynaecologist and be given another hormone treatment called a gonadotrophin-releasing hormone analogue. Since the hormonal methods used to ameliorate symptoms of premenstrual syndrome are also contraceptive, they are not appropriate if the woman is planning a pregnancy.
Selective serotonin receptor inhibitors – these are a group of medications that are used to treat depression (by elevating levels of the neurotransmitter serotonin) and have also been found to be very effective in the treatment of premenstrual syndrome. Unlike in depression, it is possible to take the medication just when experiencing symptoms, i.e. just in the second half of the menstrual cycle. This group of antidepressants may be harmful in pregnancy, so women that are planning a pregnancy should seek advice on treatment options from their doctor.
Are there any side-effects to the treatment?
Vitamin supplements and complementary therapies to relieve the symptoms of premenstrual syndrome can cause side-effects; for example, calcium supplements can cause indigestion.
With hormonal treatments, sometimes a woman can be sensitive to the hormone and experience side-effects such as nausea or breast tenderness.
Some women feel nauseated or drowsy when they first take selective serotonin receptor inhibitors but these side-effects usually settle. This medication can also affect libido (sexual drive).
Women should discuss any concerns about the treatment options or side-effects mentioned with their doctor.
What are the longer-term implications of premenstrual syndrome?
The frequency and severity of premenstrual syndrome varies from woman to woman and in each individual woman from month to month.
The greatest prevalence appears to be among women aged 30 to 50 but women can also experience a worsening of their symptoms around the time of their menopause (attributed to the erratic fluctuations in hormone levels at this time). Also it is a common time for a woman to experience stress in her life, for example as children leave home and ageing parents become more dependent. Hormone replacement therapy (HRT) can be used to treat symptoms due to the menopause and has a variable effect on symptoms experienced as part of premenstrual syndrome, which can occur during the perimenopausal period.
Premenstrual syndrome should resolve when the woman has passed her menopause as the woman no longer has a menstrual cycle with the associated cyclic release of steroid hormones from the ovary. Likewise, during pregnancy there will be no cyclical symptoms. However, women may experience similar symptoms such as abdominal bloating, breast tenderness and mood swings during pregnancy as levels of progesterone are high.
Are there patient support groups for people with premenstrual syndrome?
The National Association for Premenstrual Syndrome (NAPS) may be able to provide advice and support to patients and their families.
Last reviewed: Apr 2019
Premature ovarian failure
Estrogen and the Menstrual Cycle in Humans
Estrogen is the primary sex hormone in women and it functions during the reproductive menstrual cycle. Women have three major types of estrogen: estrone, estradiol, and estriol, which bind to and activate receptors within the body. Researchers discovered the three types of estrogen over a period of seven years, contributing to more detailed descriptions of the menstrual cycle. Each type of estrogen molecule contains a slightly different arrangement or number of atoms that in turn causes some of the estrogens to be more active than others. The different types of estrogen peak and wane throughout women’s reproductive cycles, from normal menstruation to pregnancy to the cessation of menstruation (menopause). As scientists better explained the effects of estrogens, they used that information to develop oral contraceptives to control pregnancy, to map the menstrual cycle, and to create hormone therapies to regulate abnormal levels of estrogen.
The estrogens (estradiol, estrone, and estriol) are a group of biologically active steroid hormones. As signaling molecules, estradiol, estriol, and estrone bind to receptor molecules in cells to signal specific changes to occur within the body. The estrogens each attach to receptor molecules with a specific fit, like how one puzzle piece connects to another. Some of the estrogen molecules function during the menstrual cycle, leading to changes in tissue thickness and menstrual bleeding. All three of the estrogen molecules are similar in chemical structure and constituents. The similarities of the different estrogens arise because some estrogen molecules are derivatives of the other, meaning that one estrogen can lead to the creation of another. Each estrogen molecule contains a similar base structure and varies minutely with the addition or elimination of specifically bound atoms, called functional groups. Researchers used the different functional groups to isolate and distinguish estradiol, estrone, and estriol from one another.
In the 1920s, researchers debated about what item in the female body produced most of the estrogen, then called the primary ovarian hormone, during menstrual cycles. Some researchers said that the corpora lutea, which forms on the ovaries after egg release, contained and produced the needed amount of estrogen to complete the menstrual cycle. However, researchers Edward Adelbert Doisy and Edgar Allen hypothesized that the ovarian follicles primarily produced the levels of estrogen needed to complete the cycle. In 1923 at Washington University in St. Louis, Missouri, Allen and Doisy isolated estrogen from ovarian follicle extracts and showed its effect in test animals. Their results showed that the ovarian follicles primarily produced estrogen during the reproductive cycle. That discovery enabled future researchers to outline the follicular phase, the phase in the menstrual cycle that includes egg development, to also include estrogen production in the ovarian follicles. Later researchers showed that the increase in estrogen levels led to the production of another hormone, the luteinizing hormone, which leads to the release of eggs from ovaries.
The three kinds of estrogen—estradiol, estrone, and, estriol—were discovered over time, with estrone being discovered first. In 1929, researchers Doisy, Clement D. Veler, and Sidney Thayer isolated pure crystalized estrone in the Laboratory of Biological Chemistry at the St. Louis University School of Medicine in St. Louis. The three researchers isolated estrone from the urine of pregnant women using distillation, a method that uses boiling point differences to evaporate one liquid from another; and extraction, the removal of one substance from another. At the Institute of Chemistry in Göttinge, Germany, Adolf Frederick Johann Butenandt also isolated estrone around the same time, receiving the Nobel Prize for Chemistry in 1939 for that achievement.
In addition to estrone, Doisy also isolated estriol from hundreds of gallons of urine from pregnant women in 1930, discovering a second estrogen. In 1936, Doisy alongside researchers Donald W. MacCorquodale and Stanley S. Thayer isolated the third type of estrogen, estradiol, from pig ovaries. Estradiol was later found in humans. The structure of estradiol is similar to estrone, but instead of the double bonded oxygen atom, the molecule contains a single bonded oxygen atom. The isolation of estradiol, the estrogen most involved in the reproductive menstrual cycle, enabled researchers to create hormone therapies and oral contraceptives. Doisy also researched Vitamin K, for which he went on to win the Nobel Prize in Physiology or Medicine in 1943.
Later, researchers used Doisy’s methods to create hormone therapies for women who lacked proper levels of estradiol. Researchers could cause changes in the menstrual cycle, as they had the ability to give women estradiol, the most biologically active estrogen hormone that predominates during the menstrual cycle.
In 1946 in New York City, New York, physicians Hans Wiesbader and William Filler demonstrated their ability to induce changes in the menstrual cycle when they gave lab made (synthetic) estradiol to women with problems arising from menopause. In the mid twentieth century, researchers synthesized estradiol-like molecules from other products, creating compounds like ethinyl estradiol, which caused the same reactions within the body as natural estradiol. Wiesbader and Filler sought to help women suffering from menopause, the cessation of a regular menstrual flow, by giving them the hormone ethinyl estradiol. Menopause in women can cause the vaginal tissue to thin and the natural buildup of endometrium tissue in the uterus to cease, along with symptoms like hot flashes. When women took the hormone ethinyl estradiol orally in pill form, the hormone thickened vaginal walls and uterine linings, and it removed hot-flash symptoms in some women during the clinical tests. Research with estrogen hormones continued.
The isolation of estradiol by Doisy, MacCorquodale, and Thayer also enabled researchers to create oral contraceptives, approved in 1960 in the US by the Food and Drug Administration in Washington, DC. The isolation of estradiol led researchers to describe the structure and function of the hormone, which helped chemists to cheaply synthesize estradiol-like hormones for commercial use. With the advent of synthesized estradiol, researchers made oral contraceptives available to women to prevent pregnancy. Oral contraceptives function to prevent pregnancy by altering the menstrual cycle. Those alterations prevent ovaries from releasing eggs and keep the tissue of the uterus thin, reducing the chances of a possible fertilized egg from implanting in the uterus. The menstrual cycle is controlled by estradiol and other hormones. With the discovery that estradiol functions throughout a woman’s reproductive cycle, researchers described the cycle in a greater detail.
The menstrual cycle prepares a woman’s body for possible pregnancy, producing an egg and a layer of nourishing uterine tissue. The menstrual cycle begins anew if the recently produced egg remains unfertilized or if a fertilized egg does not implant to the uterus. In humans, each menstrual cycle lasts for approximately twenty-eight days but typically varies between individuals, as some women have longer cycles and others have shorter cycles. Professionals quantify each cycle’s length by measuring the time in days that it spans from beginning to end. The monthly cycle starts on day one with normal bleeding (menstruation) and ends around day twenty-eight, just before the onset of the next menstruation if a fertilized egg has not implanted. If a fertilized egg implants to the uterine wall, the menstrual cycle stops and pregnancy begins. In humans, four regulating hormones control the menstrual cycle by initiating and ending a series of stepwise phases. The four hormones include luteinizing hormone, follicle stimulating hormone, progesterone, and estrogen. The phases that make up the menstrual cycle include the follicular phase, the ovulatory phase, and the luteal phase.
The first phase, the follicular phase, begins the menstrual cycle in humans, lasting on average thirteen to fourteen days. Egg development and menstrual bleeding both occur during the follicular phase. At the beginning of the follicular phase, the tissue that lines the inside of the uterus (endometrium) is thick and full of nutrients that are ready to support and nourish a fertilized egg. However, if an egg does not implant, the uterus shreds the endometrium. The shedding of the uterine lining is one of the many changes that occur during the menstrual cycle.
When the menstrual cycle begins, estradiol and progesterone levels drop. That drop in hormone levels signals the endometrium layer to shed, resulting in menstrual bleeding. During menstrual bleeding, the level of follicle-stimulating hormone (FSH) increases and stimulates the growth of multiple ovarian follicles. Each follicle contains a developing egg. Later in the follicular phase, FSH levels start to decrease and only one follicle grows to maturation (the dominant ovarian follicle). The dominant ovarian follicle begins producing estradiol during the follicular phase. When it begins to produce estradiol, the remaining stimulated follicles break down. The increase in estradiol stimulates the production of luteinizing hormone, which begins the next stage of a menstrual cycle.
The next phase, the ovulatory phase, lasts approximately sixteen to thirty-two hours and begins with a sharp increase in luteinizing hormone caused by estradiol at the end of the follicular phase. The surge in luteinizing hormone level causes the dominant ovarian follicle to increase in size, eventually to the point that it ruptures, releasing a mature egg from one of the two ovaries that women have. The release of an egg is called ovulation. Ovulation occurs approximately fourteen days before the onset of a woman’s next menstrual period. The released egg travels down the fallopian tube, which connects the ovary to the uterus. Once in the fallopian tube, the egg can be fertilized by sperm. If the egg becomes fertilized and implants in the uterus, the cycle stops and pregnancy occurs. Regardless of whether or not the egg becomes fertilized, the menstrual cycle continues to the luteal phase.
The luteal phase lasts for approximately fourteen days after ovulation and ends the menstrual cycle. During the luteal phase, the ruptured site on the ovary, where the dominant ovarian follicle released an egg, closes and develops into the corpus luteum. The corpus luteum produces a slight amount of estradiol and a much larger amount of progesterone. Levels of estradiol during the luteal phase are high and, together with progesterone, cause the endometrium to thicken to provide nutrients and a place for adhesion if an egg is fertilized and becomes an embryo. The increase in levels of estradiol and progesterone also causes the milk ducts in the breasts to dilate and become larger, resulting in swelling and possible breast soreness prior to the onset of menstruation. If an embryo implants to the endometrium, the corpus luteum functions until the placenta, which nourishes the fetus, develops to take over hormone production in the twelfth or thirteenth weeks of pregnancy. If a fertilized egg does not implant, the corpus luteum degrades around ten days after its initial development and stops secreting progesterone. The luteal phase ends right before the beginning of the next menstrual period or before the onset of pregnancy. The follicular phase occurs next, starting the menstrual cycle all over again.
Estradiol functions during the menstrual cycle. The drop in estradiol levels during the follicular phase causes the endometrium layer of the uterus to shed, beginning menstruation. In the later ovulatory phase, the dominant ovarian follicle produces estradiol, which increases luteinizing hormone levels, rupturing the ovarian follicle, which releases an egg. The corpus luteum during the final luteal phase produces the hormone estradiol in increasing amounts, which then thickens the endometrium, enabling the menstrual cycle to start over again. During pregnancy, the placenta produces more estriol than estradiol. Making estriol the dominant estrogen measured in blood concentration levels. Estrone increases in concentration and is produced more than estradiol when a woman enters menopause, when menstruation and the menstrual cycle stop.