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Menstrual Cycle Basics

Menstrual Cycle Basics: Understand Your Period

by Dr. Daniel J. Heller
Dr. Daniel J. Heller Dr. Daniel J. Heller

Dr. Heller is a family practitioner who specializes in helping patients with hormonal conditions like PMS & PMDD; diabetes and prediabetes; and other chronic diseases. He is the founder, formulator, and clinical director of PMS Comfort. [more]


Your menstrual cycle is the hormonal and reproductive cycle you, and all women, experience, usually monthly, typically beginning around age 12 and ending around age 50. The length of the menstrual cycle, menstrual cycle symptoms, and amount of blood flow during your period vary from woman to woman and throughout your reproductive years. Menstruation is the result of your body's hormonal and reproductive cycle, in which an egg, or ovum, is released and the uterus is prepared for pregnancy. In essence, menstruation is what happens when pregnancy does not occur.

Your menstrual cycle is probably important to you in regard to your overall health. An irregular period, menstrual or premenstrual symptoms, and concerns related to pregnancy and menstruation are foremost in many women's minds, for good reason. This article is meant to help you understand how your body and your hormones work in concert to create healthy cycles. Other articles in our library contain further information about specific menstrual cycle symptoms, including PMS symptoms, PMS cramps, menstrual pain, and other important women's health topics.

What Is a Normal Menstrual Cycle?

Because every woman is unique, there really is no such thing as a "normal" menstrual cycle, but rather, the average of what all women experience. So while it is true that the average menstrual cycle is 28 days long, many women have slightly different menstrual calendars: a cycle length from 25-35 days is well within the normal range, especially if it occurs with regularity.

While the length of the cycle can vary among women, the phases of the menstrual cycle occur in every woman. The beginning of the menstrual cycle, called the follicular phase, begins the day your period begins (so, on average, the first 3–5 days of the follicular phase is when the actual period—the menstrual flow—happens.) Once the period has ended, the lining of the uterus (the endometrium) begins to thicken. In a 28-day menstrual cycle, the follicular phase ends around day 13–15, which is when ovulation occurs—a mature egg (an ovum) is released from the ovary into the fallopian tube; from there it will travel down to the uterus. Once ovulation has occurred, it is nearly always 14–15 days until the period begins. This is called the luteal phase. The end of the luteal phase occurs with the onset of menstruation (when you get your period), which marks the beginning of the next follicular phase.
Pain accompanying ovulation—called Mittelschmerz—is normal, though not all women experience it. And, it is only normal if it is relatively slight and brief in duration. This pain is usually felt in the left or right lower section of the abdomen.

The Menstrual Cycle Through the Life Cycle

Your period—how long your cycle and your period lasts, what symptoms occur during your period or premenstrually, whether or not you have clots or spotting—will almost certainly change throughout your life, and this is perfectly normal. Menstrual pain and cramping are much more common in your teens and twenties, whereas PMS (premenstrual syndrome) symptoms can occur anytime but tend to become more pronounced in a woman's thirties and forties, although they can become more severe toward the end of a woman's reproductive years. Menopausal symptoms can begin to occur in your forties, although menopause itself does not actually begin until you've gone 6 months without a period (and, for the vast majority of women, this occurs in their late forties or early fifties).   In many women, symptoms of menopause, such as hot flashes, begin to occur before menopause.  The perimenopausal phase of life usually takes place in the mid to late forties (though, like the term menopause, it is sometimes misunderstood to be happening any time there is a change in the menstrual cycle). Perimenopause can be thought of as a cross between the symptoms of premenstrual syndrome, and the symptoms of menopause.
Not every woman will experience menstrual cycle symptoms—some women are fortunate enough to go through their reproductive years with a minimum of suffering and inconvenience. For other women, menstrual irregularities, menstrual pain, premenstrual syndrome, difficulty conceiving, complicated pregnancies, and perimenopausal and menopausal symptoms just seem like a normal part of life.

Understanding Menstrual Hormones: Estradiol, Progesterone, LH, and FSH

During the follicular phase estrogen (estradiol is the main form of estrogen) levels increase and menstrual bleeding gradually declines. During this phase, several follicles within the ovary develop, each of which contains an egg. Only one of these will develop into a mature ovum to be released, however. If, after ovulation, an ovum is fertilized, it may implant itself in the uterine lining and divide, becoming an embryo and then a fetus. During the follicular phase, there is more estrogen than progesterone in circulation in your body, as a result of the secretion of FSH, or follicle-stimulating hormone.

Ovulation occurs after a surge of luteinizing hormone (LH). The LH surge causes a surge in progesterone—a hormone that some refer to as the sister hormone of estrogen. Both estrogen and progesterone play important roles throughout the body, with the one counterbalancing and "opposing" the other when you are cycling in harmony.

After ovulation and the LH surge, the follicular tissue in the ovary that surrounded the released egg remains, and secretes large amounts of progesterone. This progesterone surge is typical of the luteal phase.

Hormones through menstrual cycle

The ovum travels through the fallopian tube to the uterus, and it is only during this 24- to (at most) 48-hour journey that the ovum can be fertilized. When an ovum is successfully fertilized, it will then attempt to attach itself, and burrow into, the endometrium of the uterus. Usually, however, this does not occur, and 14–15 days after ovulation, menstruation occurs.

Am I Pregnant?

For many women who are either concerned about becoming pregnant, or hoping to conceive, the onset of bleeding can be confusing because bleeding can occur at the expected time even if you are pregnant. Most of the time this bleeding is not a sign of problems with the pregnancy, but it can be mistaken for menstrual flow (that is, flow that occurs when the ovum has not been fertilized or when successful implantation has not occurred).

The source of this confusion is implantation bleeding. When a fertilized ovum becomes implanted in the uterine lining, some bleeding or spotting can occur. It's understandable that a woman may mistakenly think her period has become irregular, or that she isn't pregnant when in fact this can be one of the first (albeit, difficult to interpret) signs that she has become pregnant. Fortunately, we are blessed today with test kits that can provide an answer to this important question when a woman isn't quite sure—quickly, with a fair degree of accuracy, and at minimal cost.

Understanding Your Menstrual Cycle

Our health library offers informative articles to help you learn and understand how your body and your hormonal cycles work to create optimal physical and emotional wellness. If there is a subject you'd like to see covered, or you have a question about women's health, please let us know. We care, because we know what you're going through!

Real, Natural Relief—So You Can Feel Great All Month Long

PMS and PMDD misery aren't always taken seriously enough by doctors, family, and friends. At PMS Comfort, our whole purpose is to empower and educate you about premenstrual symptoms, and to provide real, natural relief so that you can feel great all month long. Our all-natural doctor-designed programs are based on decades of experience helping thousands of women recover from what you've been going through. Our Herbal Relief formula, when combined with our diet and lifestyle guidance, addresses more than just your symptoms—it can help bring your body and mind back into balance, and help you get and stay healthy. Plus, we're here to support you, every step of the way.

To learn more about your PMS and PMDD symptoms, take the PMS Comfort quiz. Or, start feeling better today, for as little as 89 cents per day.

We want to help. Give us a call at 1-800-731-6327, drop us an e-mail, or send us your question.

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Principal Author: Daniel J. Heller, N.D.
Last Modified: April 3, 2014

Menstrual Cycle—Reference Documents and Further Reading


The information and contents contained in this Web site has not been evaluated by the FDA. Products are not intended to diagnose, treat, cure, or prevent any disease. If you are pregnant, intend to become pregnant, or nursing, please consult a physician before taking any dietary supplement. If taking prescription drugs, consult your healthcare practitioner prior to use. You must be 18 years or older to purchase products. Individual results do vary.

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