Menstrual Cycle

The menstrual cycle results from the complex interaction between the reproductive system and the endocrine (hormone producing glands) system. This interaction is dedicated to the maintenance of the productive function and an appropriate hormonal balance in women. The menstrual cycle should occur on a precise cycle of every 28-30 days, and menstrual irregularity is symptom of a problem lurking somewhere in the two systems (reproductive and endocrine).

We can use headaches as an analogy. Headaches can be caused by stress, neck strain, eye fatigue, vascular disease, brain tumors, and many other problems. The nature of a headache may not reveal its cause which can be in any one of many systems (vision, vascular, brain, etc.). With menstrual irregularity, as with headaches, the irregularity is not specifically due to a particular problem in the womb, but may be the end result of many different diseases. To understand the causes of irregular cycles, we first must review the physiologic (or body function) regulation of the menstrual cycle.

Firstly, the most obvious organ involved in the menstrual cycle is the uterus. The uterine lining (endometrium) sheds (menstruates) on a cyclic basis every 28 days. This cyclic shedding of the uterine lining is controlled by a cyclic variation in the levels of two types of hormones known as estrogens and progesterone are produced by the ovaries. The structure in the ovaries containing the maturing egg and the follicle produces estrogen during the first half of the menstrual cycle. The estrogen stimulates the growth of the uterine lining (endometrium). After ovulation (release of the egg from the follicle), near the middle of the cycle, progesterone is produced by the follicular cells remaining from the ovulation (the corpus luteum).

Progesterone causes changes in the endometrial lining which prepare it for pregnancy. If pregnancy does not occur, the progesterone levels decrease, and the endometrium is shed. This action results in a menstrual flow approximately on the 28th day of the menstrual cycle. Disturbances of follicular development will therefore result in a disturbed menstrual cycle. When birth control pills are given to a woman for an abnormal menstrual cycle, they will supply progesterone and estrogen in a cyclic fashion and thus artificially induce cyclic (monthly) growth and shedding (menstruation) of the uterine lining. This treatment will provide for regular bleeding episodes (“periods”), but at the same time it will mask the primary problem rather than correct the underlying disease. Here are some specific conditions which may be responsible for irregular menstrual cycles:


Local conditions such as uterine or cervical cancer, polyps (outgrowths), or infections can produce bleeding or a discharge at irregular intervals and at unexpected times. However, in the absence of any of the above causes, irregular bleeding from the uterus is typically caused by a disturbed cyclic hormone production by the ovaries. A pelvic examination and a Pap smear can detect some of these problems. In most instances hormonal tests, an ultrasound examination, or endometrial sampling may be needed to evaluate these problems and determine precise treatment.


Estrogen causes the endometrial cells to multiply and thicken the endometrium. If this thickening continues without pause the endometrium becomes so swollen that pieces of it can break off and heavy bleeding can occur. Progesterone is the hormone responsible for halting the multiplication of the endometrial cells and maturing the endometrium. With adequate exposure to progesterone, the endometrium will peel off cleanly at the end of a cycle without heavy bleeding. This progesterone induced cyclical sloughing of endometrial tissue is very important as it stops the endometrial cells from becoming cancerous. Elevated estrogen levels and deficient progesterone levels can result in the absence of periods and/or excessive bleeding. Remember, after puberty, the absence of a period is never normal.

Ovarian Disturbances

The ovaries are regulated by the hormones FSH (follicle stimulating hormone) and LH (luteinizing hormone), produced in a cyclic fashion by the pituitary gland. The ovaries can fail to function for a variety of reasons. The most serious reason is the lack of eggs in the ovary. This condition can result from natural menopause or from an autoimmune disease in which the immunologic defense system of the body attacks the ovary for reasons that are not yet fully understood. Laboratory testing can diagnose failing ovaries by the determination of an elevated FSH level or the Anti-Mullarian Hormone (AMH) . As mentioned above, FSH is the main hormone of the pituitary gland which regulates the growth and maturation of the eggs. When the number of the eggs in the ovary is low, blood levels of FSH increase in an attempt to further stimulate an ovary that is no longer capable of responding. The AMH level drops since the number of eggs and follicles (ovarian reserve) are low. These high FSH levels and low AMH serve as a marker of ovarian failure, which translates to mean a lack of eggs in the ovaries.

Pituitary Disorders

Since menstrual bleeding is controlled by the ovarian cycles of follicular growth, maturation, and ovulation, and since the cycles, in turn, are regulated by the cyclic changes in the pituitary hormones FSH and LH, it is apparent that disturbances in the pituitary will result in ovarian and menstrual cycle disturbances. The pituitary hormones, FSH and LH, are controlled by a center in the brain called the hypothalamus. The hypothalamus produced a hormone called GnRH, which is released in a pulsatile (or rhythmic, throbbing) fashion. This pulsatile release of GnRH is the clock which ultimately regulates the menstrual cycle. Disturbances of this clock or disturbances in the pituitary gland itself may result in an inadequate or inappropriate production of FSH and LH, which in turn, results in abnormal ovarian function.

Causes of ovarian abnormalities are varied. Laboratory findings may show low FSH and LH levels. These are clues that a problem exists in the higher regulatory centers. Causes for such abnormalities include the presence of certain drugs, anorexia nervosa, chronic malnutrition, severe chronic exercise, tumors, vascular damage to the pituitary gland as a result of a difficult birth, head injuries, or genetic disorders.

Another pituitary hormone (prolactin), if present in high amounts, will interfere with regulation of the ovaries. This conditionmay be caused by tumors or various medications. The nature of the particular disorder dictates specific evaluation and appropriate therapy. In cases of prolactin secreting tumors, medical therapy is effective in reducing the prolactin levels and shrinking the tumor. In some cases, however, surgery may be an option. For some patients with normal prolactin levels, excessive amounts of prolactin can be released in response to stress or at the time of ovulation. This problem can be diagnosed by performing a TRH (thyroid releasing hormone) stimulation test. In this test, the hormone which normally stimulates prolactin in the body is injected into a vein, and blood levels of prolactin are measured over time. An excessive response of prolactin to the injection of TRH indicates a hyperstimulation problem that can be treated with medication.

The Adrenal Glands

The adrenal glands can influence ovarian function through the production of male hormones. In some patients the amount of male hormones produced by the adrenal is excessive. This excessive production may be due to a tumor in the pituitary gland, a tumor in an adrenal gland itself or a metabolic disorder. Most commonly, the adrenal glands overproduce male hormones due to metabolic disorder. The cause of this condition is not entirely clear. It is most likely a genetic problem that could have been present for many years. The excess of male hormones can produce a variety of symptoms such as oily skin, acne, increased body hair growth, and disordered ovulation – which often results in cystic ovaries, PMS, and infertility. These conditions can be treated successfully by androgen suppression therapy.

Thyroid Disorders

Both “over” and “under” activity of the thyroid gland can also lead to menstrual irregularity. Thyroid hormone levels can affect the metabolism of both male and female hormones and interfere with the regulation of ovarian function. Thyroid disorders can be properly evaluated by the use of specific laboratory tests. These tests should include an ultrasensitive thyroid stimulating hormone or TSH evaluation which tests the pituitary gland’s response to the circulating levels of thyroid hormone. The thyroid releasing hormone or TRH test can also be of value in differentiating between normal and low thyroid levels in borderline low thyroid disorders. The TRH test is the most reliable test of thyroid function in the absence of pituitary disease.


The regulation of the menstrual cycle is quite complex. Irregular periods are an important symptom which can be suggestive of underlying serious endocrine disease. An attempt to regulate menstrual cycles by the administration of birth control pills without adequate evaluation or ignoring the problem because of the “convenience” of having infrequent menses (or periods) can lead to delay in the diagnosis of a significant medical problem that could be easily treated. An appropriate evaluation of these problems requires the efforts of a specialist in endocrine disorders trained to recognize the subtle signs of reproductive dysfunction and the appropriate use of a laboratory specialized in hormonal determinations. With the recognition that reproductive system disorder are widespread among women and usually go unevaluated or unrecognized, it is especially important for women to have an understanding of the significance of menstrual disturbances and the effect on their overall health. Finally, there are new surgeries which have been developed for the management of excessive menstruation which are simple, relatively inexpensive, with virtually no convalescence or pain. These are called hysteroscopic endometrial ablation.