The female cycle

The female menstrual cycle can be divided into three phases.

Phase I begins on the first day of menstrual bleeding, and normally includes a few infertile days after menstruation.

Phase II begins as soon as a woman’s daily observations detect the onset of signs of fertility. This fertile time lasts up to and a few days after the time of ovulation (when an egg is released from the ovary). In a normal, healthy woman, Phase II will typically last approximately eight to 12 days.

Phase III is the post-ovulation time and is a time of infertility. Phase III typically accounts for the last one-third of a healthy woman’s cycle.

The three phases of the female cycle are the result of hormones — chemical messengers that are produced in one part of the body and transported by the bloodstream to another part of the body to bring about some physiological activity. Indeed, it is the interplay or interaction of a number of hormones that produces signs of fertility, and when these signs of fertility are observed and recorded, couples can identify the fertile and infertile phases of the cycle.

For those who are REALLY interested in the details of the hormonal interactions that take place in a woman’s body, see hormones affecting the female cycle.

For more on how signs of fertility are used in CCL’s NFP method, go to Sympto-Thermal Method of NFP.