Menstrual Cycle Phases

Roughly every 28 days, a new menstrual cycle begins. But few of us are aware of the delicate dance our body goes through every month and how menstrual cycle basics impact us.

We sometimes seem to think there’s just our period and a few non-period weeks. But the truth is there are four phases of the human menstrual cycle to understand (in fact there are more, but we’re going to keep it simple).

For women trying to become pregnant, understanding these phases will help you understand your fertility and the “fertile window.” But, more generally, this will help you understand your body better, which will also help you:

• Discuss any concerns about your menstrual symptoms, cycle, or hormonal changes with your healthcare provider
• Notice any unusual changes in your menstrual cycle

Menstrual Period Versus Menstrual Cycle

First things first: Your menstrual period (i.e., the 5–7 days you have your period for roughly every month) is NOT the same as your menstrual cycle.

Your menstrual cycle is the entire month-long cycle (or on average 28 days) that your body goes through to prepare for the possibility of fertilization and pregnancy. 

Your menstrual period is just one phase of that menstrual cycle, as you’ll see in the next section.

4 Main Phases of the Menstrual Cycle

Your monthly menstrual cycle can be divided into 4 important phases. 

1. Menstruation
2. Follicular phase
3. Ovulation
4. Luteal phase

It’s important to note that when your cycle begins, menstruation overlaps with the follicular phase. Or if we were to map out the phases of the menstrual cycle on a timeline based on an average 28-day menstrual cycle, it would look like this:

It’s worth noting that while the average menstrual cycle is 28 days, many women experience shorter cycles (around 21 days) and some women experience longer cycles (up to 35 days). Moreover, many women experience irregular menstrual cycles, which can be caused by many factors. Do not be alarmed if your body doesn’t run like steady clockwork.

You’ll also notice there are 2 additional stages in the chart above. We’ll discuss them more briefly towards the end of this article. 

For now, we’re going to walk through each of these 4 main phases one by one, explaining what’s happening, the role of hormones, and symptoms that you might experience during each phase.

1. Follicular Phase

The follicular phase begins on the first day of menstrual bleeding (and the first day of your cycle) and ends when ovulation occurs (approximately day 14 of the average cycle).

Hormones affecting this phase are:

• Your pituitary gland releases follicle stimulating hormone (FSH)
• Each follicle also sets off a surge of estrogen

These hormones stimulate the ovary to grow 5–20 tiny follicles, which bead on the ovary’s surface. Each follicle contains an oocyte (immature egg). Just one of those oocytes will mature into an egg or ovum that will be released in the next phase (ovulation). The other immature eggs die.

The Importance of Follicle Stimulating Hormone

The growth of the follicles (which is triggered by follicle stimulating hormone released from the pituitary gland) also sets off a surge of estrogen and progesterone that stimulates the uterine lining to thicken in preparation for a possible pregnancy.

Signs & Symptoms of the Follicular Phase

The follicular phase itself is usually unobserved. However, while your ovaries are busy preparing for fertilization, there’s a different story happening in your uterus and that definitely has symptoms you’ll be aware of.

2. Menstrual Phase

For the first 5 days of your follicular phase, you’re probably oblivious to what’s happening in your ovaries but acutely aware of what’s happening in your uterus. This is when your uterus sheds its lining from the previous month’s menstrual cycle, resulting in the menses cycle, menstrual bleeding, or period. 

Remember that the first day of your period is the first day of your normal menstrual cycle.

This phase starts because the egg from the previous menstrual cycle was not fertilized. You shed your uterine lining (endometrium) to start over the process of preparing for pregnancy. During menstrual bleeding (or your period), you shed that uterine lining through your vagina.

Signs & Symptoms of the Menstrual Phase

This is the phase of their menstrual cycle that most women are very aware of. Although there's normal variation and the severity of these symptoms can vary woman to woman, there are few who experience nothing when menstruation begins. These symptoms are usually at their worst earlier in your menstrual flow.

• Abdominal cramps: Abdominal cramping (called primary dysmenorrhea) is a common symptom of menstruation. It can range from sharp to dull pain and from general to localized. Many find that exercise, a warm bath, or heating pad can offer relief.
• Breast tenderness: Rising estrogen levels stimulate the milk ducts in your breasts, which can result in tenderness.
• Bloating or fluid retention: Nope, it’s not your imagination! Fluctuations in estrogen and progesterone levels can cause your body to retain more water. That results in a bloated feeling.
• Lower back pain: Uterine and abdominal contractions can cause lower back pain.
• Headaches: Hormone fluctuations can also cause headaches.
• Acne: Some women notice an acne breakout before or during their period. These breakouts are often on the chin or jawline but can also be on other body parts including the back. 
• Diarrhea or constipation: The prostaglandins that cause your uterus to begin contracting can also affect your bowels, causing bowel issues. 
• Low energy, fatigue: As hormone levels plummet, you may experience a drop in your energy levels.
• Mood-related symptoms, including cravings and mood swings.
• Trouble sleeping: All these symptoms can interrupt sleep for many women, compounding the difficulty of their period.

Once your period ends, your follicular phase continues, until your body moves into the ovulatory phase...

3. Ovulation

During reproductive ages, the ovary releases an oocyte (immature egg) every month. Ovulation occurs when ovary follicles rupture and release the oocyte which travels to the fallopian tube and becomes an ovum or egg. The rupture of the ovary follicles can cause some light spotting and some women can even feel it happen.

The ovulatory phase is controlled by the hypothalamus of the brain and through the release of hormones (e.g., luteinizing hormone, or LH). This means that ovulation can be impacted by hormone levels and stressors.

Hormones affecting this stage are: High levels of luteinizing hormone.

"The ovulatory phase begins with a surge in luteinizing hormone and follicle-stimulating hormone levels," according to the Merck Manual of Diagnosis and Therapy. 

"Luteinizing hormone stimulates egg release (ovulation), which usually occurs 16 to 32 hours after the surge begins. The estrogen level decreases during the surge, and the progesterone level starts to increase."

After the oocyte is released from the ovary, it moves into the fallopian tube. At this point it is called an ovum or egg. The egg stays in the tube for about 24 hours, waiting for a single sperm to fertilize it.

If the egg is not fertilized during that time, it disintegrates (breaks down) and menstrual bleeding (your period) begins 11–16 days later.

Signs & Symptoms of Ovulation

• Your basal body temperature falls: Your basal body temperature drops a little bit just before your ovary releases an oocyte. Then, 24 hours after its release, your temperature rises and stays up for several days. 
• Cervical mucus changes: The changes in your discharge over the course of your menstrual cycle also hold clues about when you might be ovulating. If your cervical mucus is:
• Dry or sticky: It’s unlikely you’re ovulating
• Creamy: Ovulation may be coming
• Wet or watery: Ovulation may start soon
• Wet and stretchy (egg white texture): You may be ovulating
• Your cervix softens and opens up: As you approach your most fertile time, your cervix softens. This is sometimes known as having a short, high, open, and wet cervix (SHOW). 
• You may experience a slight twinge or cramping: “Mittelschmerz” translates literally as “middle pain” and is the name for the slight twinge or cramp that some women experience when the follicle releases the oocyte.
• Spotting: When the ovaries release the oocyte, a tiny follicle ruptures to allow it to be released. This can be a cause of spotting for a day or so.

4. Luteal Phase

When you ovulate, an oocyte bursts from its follicle in your ovary. As previously mentioned, some women experience a little spotting from the follicle rupturing.

That ruptured follicle stays on the surface of the ovary. Over the course of the next 2 weeks—the luteal phase—that follicle transforms into a structure known as the corpus luteum, which produces progesterone.

"During the luteal phase, luteinizing hormone and follicle-stimulating hormone levels decrease," according to the Merck Manual of Diagnosis and Therapy.

Estrogen levels are high during most of this phase. Coupled with high progesterone levels produced by the corpus luteum, these hormones maintain the thickened lining of your uterus in preparation for implantation of a fertilized egg.

At that point, there are 2 options:

1. The egg is fertilized and implants: In this case, the fertilized egg itself produces the hormones that are necessary to maintain the corpus luteum and it continues to produce progesterone to maintain the thickened lining of the uterus (endometrium). The corpus luteum continues to function in early pregnancy, helping to maintain it. Among the hormones produced by the fertilized egg is human chorionic gonadotropin (HCG), which is detected in urine during a pregnancy test.
2. The egg is not fertilized and pregnancy does not occur: In this case, the corpus luteum withers and dies. This happens around day 22 in a 28 day menstrual cycle. Once the corpus luteum dies, progesterone levels drop and this causes the lining of the uterus to fall away. This causes menstruation… and the menstrual cycle starts all over again!

The average length of the luteal phase is 14 days.

Signs & Symptoms of the Luteal Phase

If you don’t get pregnant during this luteal phase, you may experience symptoms of premenstrual syndrome (PMS). You will notice that a lot of these symptoms are also symptoms of menstruation. These include:

• Bloating and fluid retention
• Breast tenderness
• Mood related symptoms, including cravings and mood changes
• Heachaches
• Trouble sleeping

The luteal phase lasts for 11 to 17 days. The average length is 14 days.

2 Other Phases

There are 2 other phases that are less commonly mentioned. These phases occur in the uterus (as does the menstruation phase). They are:

1. Proliferative phase: “The proliferative phase is the second phase of the uterine cycle when estrogen causes the lining of the uterus to grow, or proliferate, during this time. As they mature, the ovarian follicles secrete increasing amounts of estradiol, and estrogen. The estrogens initiate the formation of a new layer of endometrium in the uterus, histologically identified as the proliferative endometrium.” (Source)
2. Secretory phase: “The secretory phase is the final phase of the uterine cycle and it corresponds to the luteal phase of the ovarian cycle. During the secretory phase, the corpus luteum produces progesterone, which plays a vital role in making the endometrium receptive to implantation.” (Source) 

Factors that Can Disrupt Your Menstrual Cycle

Your menstrual cycle is a very delicate process and fluctuations in hormone levels can disrupt it. Odds are most of us have experienced a late period due to stress, or even missed periods. 

Some of the factors that can disrupt your menstrual cycle can also be cause for medical concern. But that doesn’t mean you should panic. Here are some of the many things that can have an impact:

• Stress & anxiety: Stress can throw your body for a loop and this includes your menstrual cycle.
• Exhaustion: Feeling jet lagged or suffering from insomnia? It’s not unusual that this would impact your cycle.
• Diet & eating disorders: Nutrition is key for general well-being, including reproductive health. People with eating disorders may find their cycles disrupted.
• Pregnancy: Pregnancy obviously stops your monthly cycle as fertilization and implantation stop your period (i.e., menstrual bleeding). 
• Polycystic ovary syndrome (PCOS): Women with polycystic ovary syndrome may have infrequent or prolonged menstrual periods or excess male hormone (androgen) levels. The ovaries may develop numerous small collections of fluid (follicles) and fail to regularly release eggs.
• Uterine fibroids or polyps: Fibroids are benign growths that can cause heavy bleeding and disrupt your cycle. They can also cause pain and discomfort.
• Birth control & other medications: Hormonal birth control deliberately sets out to interrupt your natural menstrual cycle in order to prevent pregnancy. Side effects of other medications can also result in hormonal changes that disrupt the cycle—delaying when your cycle starts or otherwise affecting your next cycle.
• Perimenopause: This is the final stage of your reproductive life before menopause (when periods cease completely) and is usually characterized by an irregular menstrual cycle as periods gradually stop. Menopause is diagnosed when you go 12 months without a period.

When to See a Doctor

If you experience any of the following, it’s worth scheduling a checkup with your doctor to discuss your cycle:

• Heavy periods with a lot of clotting in menstrual blood (especially clots larger than a quarter)
• Irregular periods
• Spotting between periods accompanied by abdominal pain or cramping
• Pain or a burning sensation when peeing
• Unusual vaginal discharge and/or redness and itchiness

Even if you don’t have any of the above symptoms, always visit the doctor in the following situations:

• If you think you’re pregnant: You should always see a doctor as soon as you think you might be pregnant to be administered a pregnancy test.
• If you experience inconsistent spotting: If spotting seems to happen frequently and randomly, you should definitely look into it.
• Bleeding or spotting begins after unprotected sex: Unprotected sex can put you at risk for sexually transmitted infections (STIs) and other infections. So, if you notice spotting after unprotected sex, it’s wise to visit a doctor.
• Postmenopausal vaginal bleeding: You’ve been through menopause and you experience vaginal bleeding.

Written by Jane Flanagan — Updated on April 5, 2022.

We hope you found this post informative — but remember: we’re not doctors and this post is not medical advice! While all posts are fact-checked and well researched, we always recommend you chat with your doctor about any questions or concerns you might have regarding a medical condition. We’re here to support and educate, but never with the aim of disregarding professional medical advice you’ve been given. Phew, now that that’s out of the way, you can go on living unapologetically free.