Every woman's body is unique, and so are their menstrual cycles.  The cycle begins on the first day of bleeding and continues to the first day of the next menstrual period.  This cycle usually takes an average of  28 days, however this can vary from as short as  23 days to as long as 35 days.  For some women, each cycle is different from the previous.   What is irregular for one woman may be normal for another. 
 
Doctors consider the normal volume for menstrual flow to be about 30 to 80 milliliters (2 tablespoons to about 1/3 cup);.  Anything less or more than that could be considered abnormal menstrual bleeding. If a woman has irregular or abnormal menstrual bleeding, a doctor may prescribe hormones or other therapies to help regulate her period.  Irregular menstruation and abnormal menstrual bleeding fall into several different categories.

Amenorrhea is the failure to start menstruation during puberty or cessation of menstruation. Some of the normal causes of amenorrhea are pregnancy, lactation and menopause. Primary amenorrhea is present when a young woman has not started to menstruate by age 16. This may be because she has some hormonal imbalance or developmental problem, which can often be treated with hormones and/or surgery.

Amenorrhea, more commonly, affects women who have previously had normal periods. It is defined as an absence of menstruation for a length of time equivalent to a total of at least three of the previous cycle intervals or six months.  Secondary amenorrhea is usually caused by a a hormone imbalance. 

Dysmenorrhea is the medical term for menstrual cramps. Primary dysmenorrhea is not caused by an underlying medical condition and generally begins when a girl first starts having her period. With primary dysmenorrhea, no disease or other medical cause can be found for the pain and other symptoms, which may include backache, diarrhea, dizziness, headache, nausea, vomiting, and a feeling of tenseness. Primary dysmenorrhea frequently affects women in their teens and early 20s, who have never had a baby.

The symptoms are caused by prostaglandin, a natural hormone produced by cells in the uterine lining. The level of prostaglandin increases in the second half of the menstrual cycle. When a woman’s period begins, the cells in the uterine lining release prostaglandin as they are shed. Women with severe primary dysmenorrhea have significantly higher prostaglandin levels in their menstrual fluid than do other women.

The only good thing that can be said about primary dysmenorrhea is that usually the symptoms don’t last very long. Some women experience symptoms for up to one or two days, but rarely longer.

Secondary dysmenorrhea typically occurs later in life and is the result of a problem with the woman's reproductive system. Secondary dysmenorrhea is caused by a physical condition. Women who suffer from it tend to be older than those with primary dysmenorrhea. Some conditions that may be responsible for secondary dysmenorrhea are

§         adenomyosis (uterine tissue growing into the uterine wall).

§         endometrial polyps (growths in the uterine lining).

§         endometriosis (uterine tissue that grows outside the uterus, in the ovaries and other locations). Endometriosis is the most common reason for secondary dysmenorrhea.

§         fibroids (growths in the uterus).

§         narrowing of the cervix (the entrance to the uterus) as it opens into the vagina.

§         pelvic inflammatory disease (PID).

§         use of an intrauterine device (IUD).

Menorrhagia is excessively heavy or prolonged  uterine bleeding that occurs as a normal part of a woman's menstrual cycle.  Blood flow may be high in volume (over 80 milliliters—about 1/3 cup) and may last longer than a normal period (usually eight to ten days).  Menorrhagia may be caused by medical problems or hormone imbalances.

Dysfunctional or abnormal uterine bleeding is a problem that often affects women as they start to get periods and as they get closer to menopause — although it can occur in any woman who menstruates. The main symptoms are prolonged and/or irregular menstrual bleeding. The bleeding may occur as irregular spotting during the cycle, but sometimes the bleeding is so heavy that a woman can't participate in her normal day-to-day activities, such as work and exercise.  Dysfunctional utering bleeding  occurs because of a hormone imbalance in the body and not by a specific condition such as polyps or uterine fibroids (growths), cancer, or complications of pregnancy.  While it may be somewhat reassuring for a woman to know the bleeding is not caused by disease, it is still very troublesome and must be investigated and treated. 

Premenstrual syndrome, or PMS, is a group of physical and emotional symptoms that occur in the latter half of the menstrual cycle following ovulation. Symptoms, which can include backache, bloating, irritability and headache, are typically most intense during the seven days prior to the start of menstruation. Fortunately, a woman obtains relief when her menstrual period begins.

Premenstrual dysphoric disorder, or PMDD, is a more severe form of PMS that also includes a psychological component.  Like PMS, PMDD occurs the week before the onset of menstruation and disappears a few days after. PMDD is characterized by severe monthly mood swings and physical symptoms that interfere with everyday life, especially a woman’s relationships with her family and friends. PMDD symptoms go far beyond what are considered manageable or normal premenstrual symptoms. 

PMDD is a combination of symptoms that may include irritability, depressed mood, anxiety, sleep disturbance, difficulty concentrating, angry outbursts, breast tenderness and bloating. The diagnostic criteria emphasize symptoms of depressed mood, anxiety, mood swings or irritability.   Several forms of prescription medications have been found to be effective in treating the symptoms of PMDD.