The menstrual cycle starts with the first day of the period and ends when the next period begins. Your menstrual cycle can say a lot about your health.

The menstrual cycle is the monthly series of changes a woman’s body goes through in preparation for the possibility of pregnancy. Each month, one of the ovaries releases an egg a process called ovulation. At the same time, hormonal changes prepare the uterus for pregnancy. If ovulation takes place and the egg isn’t fertilized, the lining of the uterus sheds through the vagina. This is a menstrual period.

Most women experience mild symptoms in the few days leading up to menstruation and in the first day or two of menstruating when the flow of blood is heavier.

Here are some of the normal physical symptoms of menstruation :

• Tender breasts
• Bloating, fluid retention
• Muscle aches
• Joint pain
• Headaches
• Acne
• Abdominal cramps
• Diarrhea or constipation
• Lower back pain
• Trouble sleeping
• Low energy, fatigue
• Food cravings
• Tiredness
• Mood changes

The menstrual cycle includes several phases. The exact timing of the phases of the cycle is a little bit different for every woman and can change over time.

Days 1-5 : The first day of menstrual bleeding is considered Day 1 of the cycle. Your period can last anywhere from 3 to 8 days, but 5 days is average. Bleeding is usually heaviest on the first 2 days.

Days 6-14 : Once the bleeding stops, the uterine lining (also called the endometrium) begins to prepare for the possibility of a pregnancy.The uterine lining becomes thicker and enriched in blood and nutrients.

Day 14-25 : Somewhere around day 14, an egg is released from one of the ovaries and begins its journey down the fallopian tubes to the uterus.If sperm are present in the fallopian tube at this time, fertilization can occur.In this case the fertilized egg will travel to the uterus and attempt to implant in the uterine wall.

Days 25-28 : If the egg was not fertilized or implantation does not occur, hormonal changes signal the uterus to prepare to shed its lining, and the egg breaks down and is shed along with lining.

The cycle begins again on Day 1 menstrual bleeding.

Menstrual cycle irregularities can have many different causes, including:

• Pregnancy or breast-feeding A missed period can be an early sign of pregnancy. Breast-feeding typically delays the return of menstruation after pregnancy.

• Eating disorders, extreme weight loss or excessive exercising. Eating disorders — such as anorexia nervosa — extreme weight loss and increased physical activity can disrupt menstruation.

• Polycystic ovary syndrome (PCOS). Women with this common endocrine system disorder may have irregular periods as well as enlarged ovaries that contain small collections of fluid — called follicles — located in each ovary as seen during an ultrasound exam.

• Premature ovarian failure. Premature ovarian failure refers to the loss of normal ovarian function before age 40. Women who have premature ovarian failure — also known as primary ovarian insufficiency — might have irregular or occasional periods for years.

• Pelvic inflammatory disease (PID). This infection of the reproductive organs can cause irregular menstrual bleeding.

• Uterine fibroids. Uterine fibroids are noncancerous growths of the uterus. They can cause heavy menstrual periods and prolonged menstrual periods.

In addition, consult your health care provider if :

• Your periods suddenly stop for more than 90 days and you’re not pregnant

• Your periods become erratic after having been regular

• You bleed for more than seven days

• You bleed more heavily than usual or soak through more than one pad or tampon every hour or two

• Your periods are less than 21 days or more than 35 days apart

• You bleed between periods

• You develop severe pain during your period

• You suddenly get a fever and feel sick after using tampons

If you have questions or concerns about your menstrual cycle, talk to your health care provider.