Menstrual Cycle: How Your Period Works & What to Expect

What Is Menstruation and Why Does It Happen?

Menstruation is the monthly shedding of the uterine lining (endometrium) that occurs when pregnancy has not happened. The body prepares for pregnancy each month by thickening the uterine lining with blood and nutrients, and when an egg isn't fertilized, hormone levels drop and the lining is shed through the vagina as your period.

Menstruation, commonly called your period, is a natural biological process that typically begins during puberty and continues until menopause. It represents one part of a complex hormonal cycle that prepares the female body for potential pregnancy each month. Understanding this process helps you make sense of the physical and emotional changes you may experience throughout your cycle.

The menstrual cycle is much more than just your period. It encompasses a series of hormonal changes and physical events that occur in the ovaries, uterus, and other parts of the reproductive system. The average cycle lasts 28 days, though cycles ranging from 21 to 35 days are considered perfectly normal. The cycle is counted from the first day of one period to the first day of the next period.

Each cycle, your ovaries release an egg (ovulation), and your uterus prepares a thick, nutrient-rich lining in case the egg is fertilized. If fertilization doesn't occur, hormone levels drop, signaling the uterus to shed its lining. This shedding, which exits through the cervix and vagina, is what we experience as menstrual bleeding. The entire process then begins again.

When Does Menstruation Start and End?

Menstruation typically begins between ages 10 and 16, with the average age being around 12 years old. This first period is called menarche. The timing of menarche is influenced by genetics, nutrition, body weight, and overall health. It's common for periods to be irregular during the first few years as the body adjusts to hormonal changes.

Menstruation continues until menopause, which typically occurs between ages 45 and 55, with the average age being 51. The transition to menopause, called perimenopause, can begin several years earlier and is characterized by increasingly irregular periods until they stop completely. A woman is considered to have reached menopause after 12 consecutive months without a period.

What Happens Inside Your Body During Menstruation?

During menstruation, the uterus contracts to help expel the lining. These contractions are triggered by hormone-like substances called prostaglandins, which are also responsible for menstrual cramps. Higher levels of prostaglandins lead to more intense contractions and potentially more discomfort.

The menstrual fluid consists of blood, mucus, and tissue from the uterine lining. Contrary to common perception, the amount of blood lost during a typical period is relatively small, approximately 30-80 milliliters (about 2-6 tablespoons) over the entire period. The first two days are usually the heaviest, with flow gradually decreasing over the following days.

What Are the Four Phases of the Menstrual Cycle?

The menstrual cycle has four distinct phases: menstruation (days 1-5), the follicular phase (days 1-13), ovulation (around day 14), and the luteal phase (days 15-28). Each phase is characterized by specific hormonal changes that prepare the body for potential pregnancy or trigger menstruation if pregnancy doesn't occur.

Understanding the four phases of your menstrual cycle can help you anticipate physical and emotional changes throughout the month. While the following description uses a 28-day cycle as a reference, remember that your individual cycle may be shorter or longer, and the timing of each phase will adjust accordingly.

Phase 1: Menstruation (Days 1-5)

Menstruation marks both the end of one cycle and the beginning of the next. During this phase, the uterine lining that built up during the previous cycle is shed through the vagina. This occurs because estrogen and progesterone levels have dropped, signaling that pregnancy has not occurred.

Most people bleed for 3 to 7 days, with the heaviest flow typically occurring during the first 2 days. During menstruation, you may experience cramping, bloating, breast tenderness, mood changes, and fatigue. These symptoms are caused by hormonal fluctuations and the release of prostaglandins that trigger uterine contractions.

Phase 2: Follicular Phase (Days 1-13)

The follicular phase begins on the first day of your period and continues until ovulation. During this phase, the pituitary gland releases follicle-stimulating hormone (FSH), which stimulates the ovaries to produce several follicles. Each follicle contains an immature egg.

As the follicles develop, they produce estrogen, which has several important effects. Estrogen causes the uterine lining to thicken and become rich with blood and nutrients, preparing a hospitable environment for a potential embryo. Rising estrogen levels also trigger the pituitary gland to reduce FSH production, which eventually allows one dominant follicle to emerge.

Many people feel their best during the later part of the follicular phase. Energy levels tend to increase, mood often improves, and some people notice enhanced cognitive function and creativity. This is due to rising estrogen levels, which have positive effects on neurotransmitters like serotonin and dopamine.

Phase 3: Ovulation (Around Day 14)

Ovulation is the release of a mature egg from the ovary. It typically occurs around day 14 of a 28-day cycle, though the timing can vary significantly between individuals and even from cycle to cycle in the same person. Ovulation is triggered by a surge in luteinizing hormone (LH) from the pituitary gland.

The released egg travels through the fallopian tube toward the uterus. An egg can only be fertilized for about 12-24 hours after ovulation. However, because sperm can survive in the reproductive tract for up to 5 days, the fertile window extends from about 5 days before ovulation to 1 day after.

Some people can feel when they ovulate. Signs may include a twinge or mild pain on one side of the lower abdomen (called mittelschmerz), changes in cervical mucus (which becomes clear, slippery, and stretchy like egg whites), a slight increase in basal body temperature, and increased libido.

Phase 4: Luteal Phase (Days 15-28)

After ovulation, the empty follicle transforms into a structure called the corpus luteum, which produces progesterone and some estrogen. Progesterone further prepares the uterine lining for potential implantation of a fertilized egg by making it thicker and more secretory.

The luteal phase typically lasts about 14 days and is the most consistent part of the menstrual cycle. If the egg is not fertilized, the corpus luteum breaks down, progesterone and estrogen levels drop, and this hormonal withdrawal triggers menstruation, beginning a new cycle.

The luteal phase is when many people experience premenstrual symptoms (PMS). These can include mood swings, irritability, anxiety, depression, breast tenderness, bloating, food cravings, headaches, and fatigue. These symptoms are related to hormonal fluctuations and typically improve once menstruation begins.

How Do Hormones Control the Menstrual Cycle?

Four main hormones control the menstrual cycle: FSH (follicle-stimulating hormone) stimulates egg development, estrogen thickens the uterine lining, LH (luteinizing hormone) triggers ovulation, and progesterone maintains the lining after ovulation. These hormones communicate between the brain (hypothalamus and pituitary gland) and the ovaries in a carefully coordinated feedback loop.

The menstrual cycle is orchestrated by an intricate communication system between the brain and the reproductive organs. This system, called the hypothalamic-pituitary-ovarian (HPO) axis, uses hormones as chemical messengers to coordinate the timing of each phase of the cycle. Understanding this system helps explain why factors like stress, weight changes, and certain medications can affect your period.

The process begins in the hypothalamus, a region of the brain that acts as the master controller. The hypothalamus releases gonadotropin-releasing hormone (GnRH), which signals the pituitary gland to produce and release FSH and LH. These hormones then travel to the ovaries, where they stimulate follicle development and hormone production.

Follicle-Stimulating Hormone (FSH)

FSH is produced by the pituitary gland and is essential for the early stages of the menstrual cycle. As its name suggests, FSH stimulates the growth of ovarian follicles, each of which contains an immature egg. FSH levels are highest at the beginning of the follicular phase and decrease as estrogen levels rise.

FSH plays a crucial role in fertility. Abnormal FSH levels can indicate problems with ovarian function and are often measured as part of fertility testing. High FSH levels may suggest diminished ovarian reserve, while low levels can indicate problems with the pituitary gland.

Estrogen

Estrogen, primarily estradiol, is produced by the developing follicles in the ovaries. Estrogen levels rise during the follicular phase and peak just before ovulation. This hormone has wide-ranging effects throughout the body, affecting not just the reproductive system but also bones, heart, brain, and skin.

In the reproductive system, estrogen causes the uterine lining to thicken and become more vascularized, preparing it to potentially support a pregnancy. Estrogen also changes cervical mucus, making it thinner and more hospitable to sperm around ovulation. Additionally, estrogen influences the pituitary gland through a feedback mechanism that ultimately triggers the LH surge leading to ovulation.

Luteinizing Hormone (LH)

LH is also produced by the pituitary gland and plays a critical role in triggering ovulation. When estrogen levels reach a certain threshold, the pituitary responds by releasing a sudden surge of LH. This LH surge causes the dominant follicle to rupture and release its mature egg within 24-36 hours.

Many home ovulation predictor kits work by detecting this LH surge in urine. A positive test indicates that ovulation is likely to occur within the next day or two, helping people identify their most fertile window.

Progesterone

Progesterone is produced primarily by the corpus luteum after ovulation. This hormone prepares the uterine lining for potential implantation by making it more secretory and receptive. Progesterone also raises body temperature slightly (which is why tracking basal body temperature can confirm ovulation) and has calming effects on the uterus to prevent contractions.

Progesterone is sometimes called the pregnancy hormone because it is essential for maintaining early pregnancy. If pregnancy occurs, the corpus luteum continues producing progesterone until the placenta takes over around week 10. If pregnancy doesn't occur, the corpus luteum breaks down, progesterone levels fall, and menstruation begins.

What Are Common Menstrual Symptoms and How Can You Manage Them?

Common menstrual symptoms include cramping, bloating, breast tenderness, mood changes, fatigue, and headaches. These symptoms are caused by hormonal fluctuations and prostaglandin release. Management strategies include NSAIDs (like ibuprofen), heat therapy, regular exercise, adequate sleep, and stress reduction. Severe symptoms that disrupt daily life should be evaluated by a healthcare provider.

Most people who menstruate experience some symptoms during their period or in the days leading up to it. These symptoms range from mild inconveniences to significant disruptions that affect daily life. Understanding what causes these symptoms can help you find effective management strategies and recognize when symptoms warrant medical attention.

Menstrual Cramps (Dysmenorrhea)

Menstrual cramps are the most common period symptom, affecting up to 90% of menstruating people. Primary dysmenorrhea refers to cramps that occur without an underlying medical condition and is caused by prostaglandins that trigger uterine contractions. These cramps typically begin 1-2 days before your period starts and last for 2-3 days.

The severity of cramps varies widely. Mild cramps may be barely noticeable, while severe cramps can cause significant pain in the lower abdomen, lower back, and thighs. Some people also experience nausea, vomiting, diarrhea, or headaches alongside cramps.

Effective treatments for menstrual cramps include nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen or naproxen. These medications work by reducing prostaglandin production and are most effective when taken at the first sign of cramping or even before symptoms begin. Other helpful strategies include applying heat to the lower abdomen, gentle exercise, and adequate rest.

Premenstrual Syndrome (PMS)

PMS refers to a collection of physical and emotional symptoms that occur in the luteal phase, typically in the 1-2 weeks before menstruation. Symptoms usually resolve within a few days of the period starting. Common PMS symptoms include mood swings, irritability, anxiety, depression, bloating, breast tenderness, food cravings, fatigue, and headaches.

Up to 75% of menstruating people experience some PMS symptoms, though severity varies significantly. For most, symptoms are mild and manageable. However, about 3-8% of people experience severe PMS, including a condition called premenstrual dysphoric disorder (PMDD), which involves severe depression, anxiety, and irritability that significantly interfere with daily life.

Lifestyle modifications can help manage PMS symptoms. Regular exercise, reduced salt and caffeine intake, adequate sleep, and stress management techniques are beneficial for many people. Some may also benefit from calcium and vitamin B6 supplements. Hormonal contraceptives can help regulate hormone fluctuations and reduce PMS symptoms for some people.

Heavy Menstrual Bleeding

While there's a wide range of normal when it comes to menstrual flow, some people experience heavy menstrual bleeding (menorrhagia). Signs of heavy bleeding include soaking through a pad or tampon every hour for several consecutive hours, needing to use double protection, bleeding for more than 7 days, passing blood clots larger than a quarter, and experiencing fatigue or shortness of breath (signs of anemia).

Heavy bleeding can have various causes, including hormonal imbalances, uterine fibroids, polyps, adenomyosis, bleeding disorders, or rarely, cancer. If you experience heavy bleeding, it's important to see a healthcare provider for evaluation. Treatments depend on the underlying cause and may include medications, hormonal therapy, or in some cases, surgical procedures.

Bloating and Water Retention

Many people notice bloating and mild weight gain (usually 1-3 pounds) in the days leading up to and during their period. This is caused by hormonal changes that affect how the body retains water. Progesterone, in particular, can cause fluid retention, and falling estrogen levels trigger the kidneys to retain sodium and water.

To minimize bloating, try reducing salt intake in the premenstrual phase, staying hydrated (which paradoxically helps reduce water retention), exercising regularly, and avoiding carbonated beverages. Some people find relief with potassium-rich foods like bananas and leafy greens, which can help balance sodium levels.

What Causes Irregular Periods and When Should You Be Concerned?

Irregular periods can be caused by stress, significant weight changes, excessive exercise, hormonal conditions like PCOS, thyroid disorders, perimenopause, or certain medications. Occasional irregularity is common and usually not concerning. However, you should see a doctor if you miss three or more periods in a row, have cycles shorter than 21 or longer than 35 days, or experience very heavy or prolonged bleeding.

Menstrual irregularities are common and can take various forms: cycles that are too long, too short, unpredictable, or absent altogether. While occasional variations are normal, persistent irregularities may indicate an underlying condition that needs attention. Understanding the potential causes can help you determine when to seek medical advice.

It's important to establish what's normal for you. While medical textbooks describe a 28-day cycle, individual cycles can vary significantly. Some people consistently have 24-day cycles; others may have 32-day cycles. Both can be perfectly healthy. Tracking your periods over several months helps you understand your personal pattern and makes it easier to identify meaningful changes.

Common Causes of Irregular Periods

Stress is one of the most common causes of menstrual irregularities. The hypothalamus, which coordinates the menstrual cycle, is also involved in the stress response. Significant physical or emotional stress can disrupt the hormonal signals that regulate your cycle, leading to late, missed, or irregular periods.

Weight changes, both significant weight loss and weight gain, can affect hormone levels and disrupt menstrual regularity. Very low body weight or body fat percentage can cause periods to stop altogether (amenorrhea), as the body may not have enough energy reserves to support reproduction. Obesity can also cause irregular periods by affecting estrogen levels and insulin sensitivity.

Excessive exercise, particularly in athletes, can lead to irregular or absent periods. This is often related to low body weight or energy availability, but can also result from the physical stress of intense training. This condition, sometimes called the female athlete triad, requires medical attention as it can affect bone health.

Polycystic ovary syndrome (PCOS) is a common hormonal condition affecting 5-10% of reproductive-age women. It is characterized by irregular or absent periods, excess androgens (male hormones), and polycystic ovaries on ultrasound. PCOS is associated with insulin resistance and can affect fertility.

Thyroid disorders can significantly impact menstrual regularity. Both hypothyroidism (underactive thyroid) and hyperthyroidism (overactive thyroid) can cause irregular, heavy, or light periods. The thyroid gland produces hormones that affect nearly every system in the body, including the reproductive system.

Perimenopause, the transition to menopause, typically begins in the mid-40s and is characterized by increasingly irregular periods. Cycles may become shorter or longer, heavier or lighter, and more unpredictable as hormone levels fluctuate before periods eventually stop.

When to See a Healthcare Provider

While occasional irregular periods are common and usually not concerning, certain situations warrant medical evaluation. You should see a healthcare provider if:

• You miss three or more periods in a row (and you're not pregnant)
• Your periods suddenly become very irregular after being regular
• Your cycle is consistently shorter than 21 days or longer than 35 days
• You bleed between periods or after sexual intercourse
• Your periods become much heavier or more painful than usual
• Bleeding lasts more than 7 days
• You haven't had a period by age 15
• You experience symptoms of anemia (fatigue, shortness of breath, dizziness)

How Can You Track Your Menstrual Cycle?

Track your cycle by recording the first day of each period, bleeding duration and intensity, and any symptoms throughout the month. Use a calendar, paper chart, or period tracking app. Consistent tracking for at least 3 months reveals your personal patterns and helps identify irregularities. This information is valuable for healthcare appointments and fertility planning.

Tracking your menstrual cycle provides valuable insights into your reproductive health and overall wellbeing. Whether you're trying to conceive, avoid pregnancy, manage symptoms, or simply understand your body better, consistent cycle tracking can be a powerful tool. The information you gather can also be helpful when discussing your health with medical providers.

The most basic form of cycle tracking involves recording the first day of each period. This day is considered Day 1 of your cycle. By tracking this date over several months, you can calculate your average cycle length and identify any patterns or irregularities. A consistent tracking record makes it much easier to notice if something changes.

What to Track

While noting the start of your period is a good foundation, tracking additional details provides a more complete picture of your cycle. Consider recording:

• Bleeding characteristics: Duration (how many days), flow intensity (light, medium, heavy), color, and presence of clots
• Physical symptoms: Cramps, headaches, breast tenderness, bloating, acne, fatigue, and any other physical changes
• Emotional symptoms: Mood changes, anxiety, irritability, depression, energy levels
• Cervical mucus: Changes in consistency throughout the cycle can indicate fertility status
• Basal body temperature: A slight rise after ovulation can confirm that ovulation occurred
• Sexual activity: Helpful if tracking for fertility or contraception purposes
• Lifestyle factors: Stress levels, sleep quality, exercise, travel, illness

Tracking Methods

Period tracking apps are popular and convenient. They typically allow you to log all the information mentioned above and use algorithms to predict future periods and fertile windows. Many apps also provide insights and visualizations of your cycle patterns over time. Popular options include Clue, Flo, and Apple Health's cycle tracking feature.

Paper calendars or charts work well for those who prefer a low-tech approach. Simply mark the days of your period on a calendar and note any symptoms. Some people find physical tracking more intuitive and appreciate being able to see several months at a glance.

Basal body temperature (BBT) tracking involves taking your temperature first thing every morning before getting out of bed. After ovulation, progesterone causes a slight temperature rise (about 0.5-1.0 degrees Fahrenheit) that persists until your next period. This method can confirm that ovulation occurred but doesn't predict it in advance.

Benefits of Cycle Tracking

Consistent cycle tracking offers numerous benefits. It helps you anticipate when your period will arrive so you can be prepared. It can identify patterns in symptoms, allowing you to plan around them or implement preventive strategies. For those trying to conceive, tracking can identify the most fertile days. For those avoiding pregnancy, it provides additional awareness (though it should not be relied upon as the sole form of contraception without proper training in fertility awareness methods).

Perhaps most importantly, tracking creates a record that can be invaluable for healthcare conversations. If you notice changes in your cycle or experience concerning symptoms, having detailed information helps your provider make accurate assessments and diagnoses.

When Should You See a Doctor About Your Period?

See a doctor if your periods are very heavy, very painful, or very irregular; if you miss three or more periods in a row; if you bleed between periods or after sex; if your cycle is consistently outside the 21-35 day range; or if period symptoms significantly interfere with your daily life. Don't dismiss severe symptoms as normal - many conditions causing these symptoms are treatable.

While menstruation is a normal bodily function, it's important to recognize when symptoms cross the line from inconvenient to concerning. Many people assume that severe period pain or heavy bleeding is just something they have to endure, but these symptoms can indicate treatable conditions. Early evaluation and treatment can significantly improve quality of life and prevent complications.

Generally, you should seek medical attention if your menstrual symptoms are preventing you from doing normal activities like going to school, work, or social events. Period-related symptoms that require bed rest, cause you to miss important activities, or don't respond to over-the-counter treatments deserve medical evaluation.

Signs That Warrant Medical Attention

Very heavy bleeding that soaks through a pad or tampon every hour for more than 2 hours, or requires you to change protection during the night, may indicate conditions like fibroids, polyps, or bleeding disorders. Heavy bleeding can also lead to iron-deficiency anemia, causing fatigue, weakness, and shortness of breath.

Severe pain that doesn't respond to NSAIDs and significantly affects daily functioning may be a sign of conditions like endometriosis, adenomyosis, or uterine fibroids. While some discomfort during menstruation is common, pain severe enough to make you vomit, pass out, or miss work or school is not normal and should be investigated.

Bleeding between periods (intermenstrual bleeding) or after sexual intercourse can have various causes ranging from hormonal contraceptives and cervical ectropion to infections, polyps, or rarely, cancer. Any unexpected bleeding should be evaluated by a healthcare provider.

Absent periods (when not pregnant, breastfeeding, or postmenopausal) for three or more months warrant investigation. Amenorrhea can be caused by hormonal imbalances, thyroid disorders, PCOS, premature ovarian insufficiency, or other conditions.

Sudden changes in your menstrual pattern, such as periods becoming much heavier, more painful, or more irregular when they were previously regular, should prompt a medical visit. Significant changes can indicate new health issues that need attention.

Preparing for Your Appointment

When you see a healthcare provider about menstrual concerns, being prepared helps make the most of your appointment. Bring your cycle tracking information if you have it, including dates of recent periods, duration, flow intensity, and symptoms. Be ready to describe your symptoms in detail, including when they started, how severe they are, and what makes them better or worse.

Your provider may ask about your menstrual history, sexual activity, contraception use, family history of gynecological conditions, and general health. Depending on your symptoms, they may perform a physical exam, including a pelvic exam, and order tests such as blood work, ultrasound, or other imaging studies.