Phases of the Menstrual Cycle

There are three basic phases of a woman’s menstrual cycle: pre-ovulation (the time before ovulation); ovulation (the time the egg is released by the ovary); and post ovulation (the time after the egg dies).

The first phase of the woman’s menstrual cycle begins on the first day of her monthly bleeding (menses or period) and ends on the day of ovulation (the day the woman releases a mature egg). A woman has thousands of eggs, which are housed in two small sacks called ovaries. There is one ovary on each side of the woman’s body. The ovaries are attached to fallopian tubes, which are long and thin. These tubes are connected to the womb and help to guide the egg to reach the uterus. It is in the fallopian tubes where, if present, sperm will meet egg. In the first part of the menstrual cycle, one or more of the thousands of undeveloped eggs in a woman’s body begin to develop on a signal from a chemical messenger (hormone) from the brain called follicle stimulating hormone (FSH) (see Figure 2).

As the egg develops and matures in the follicle, it gives off another important chemical or hormone called estrogen (see Figure 2). Estrogen is important for fertility because it helps the inside of the uterus (womb) to develop. It also signals special cells in the opening of the uterus to produce cervical mucus.  This mucus is called cervical mucus. Cervical mucus is an important natural indicator of fertility.

The length of the pre-ovulation phase of the cycle can change from cycle to cycle in the same woman. For example, a woman could ovulate (release an egg) on day 14 in one cycle, and in the next cycle she could ovulate on day 10. Research has revealed that a variety of factors can effect this time of the cycle. Some of those factors include: weight loss, emotional stress (good or bad),illness, too much exercise, and even diet. Despite this variety, the time of fertility can be known by a woman. A woman’s body produces a number of biological signs (or markers) which can help her know when her fertility begins, when she ovulates, and when her fertility ends.

The second phase of the menstrual cycle is ovulation.  Ovulation happens when another body chemical (Luteinizing Hormone or LH) signals the ovary to release a mature egg (see Figure 2).  The releasing of the egg is called ovulation and is the optimal time of fertility. At this time some women experience breast tenderness and swelling, abdominal pain or cramping, and vulvar swelling.  Furthermore, at this time, the cervical opening (OS) widens, softens, and fills with sperm friendly (clear-slippery) mucus.

The next and final phase of the woman’s menstrual cycle begins the first day after ovulation and ends the day before the next period. This time in the woman’s menstrual cycle is called the luteal phase and is relatively stable in length (averaging about 10-16 days in all women). 


Fig 2: Female Menstrual Cycle and Hormones

Hormone Levels – for 28-day cycle:

After ovulation, the body increases the release of another female chemical, a hormone called progesterone (see Figure 3).  Progesterone has a number of important functions. It elevates the woman’s body temperature about 0.4 – 0.8 tenths of a degree Fahrenheit. This heating up of the woman’s body can be detected by taking daily waking temperatures. Progesterone also prepares the lining of the uterus for possible implantation of a new human being. Finally, progesterone stimulates cervical cells to produce thick mucus that closes off the opening of the cervix and thus serves as a barrier to sperm and bacteria.

If an egg is fertilized by a sperm (i.e., the man’s sperm cell unites with the woman’s egg cell) a new human life will be created. The new person will travel down the fallopian tube in a 6-9 day journey. On about day 10, the baby attaches to the wall of the mother’s uterus. The uterus will then house and feed the new baby for the next 9 months. If the woman’s egg is not fertilized by the man’s sperm, the levels of progesterone will decrease, and the lining of the uterus will shed. This shedding of the lining of the uterus is experienced by the woman as bleeding and is called menstruation.