Couples who want to practice natural family planning (NFP) may use one or more of several techniques to identify the fertile phase of the menstrual cycle:
Calendar or Rhythm Method (Ogino-Knaus Method)
Women use past menstrual cycles to help them predict future fertility. For most women, menstrual bleeding begins 12 to 16 days after ovulation. While the average length of menstrual cycles is 28 days, the length of the cycle from woman to woman can vary. When women want to use the calendar/rhythm method, they record the length of six menstrual cycles, counting the first day of bleeding as the first day of a new cycle. Then they count the number of days in the shortest cycle, subtract the number 18, and use the answer to estimate the first day of fertility. To estimate the last day, they determine the number of days in the longest cycle and subtract 11. They avoid sex during the time period from the first through last possible fertile days. For example, if a woman's shortest cycle was 26 days and her longest cycle was 30 days, she would avoid sex on days eight through 19 of her menstrual cycle.
The Basal Body Temperature (BBT) Method
A woman's body temperature typically rises slightly after she ovulates (0.2 to 0.4 degrees C.), and remains elevated until the end of the cycle. The rise in temperature is thought to be due to the production of the hormone, progesterone. Women who use this method must chart their temperature every day, immediately after waking up and before getting out of bed or drinking any liquids. Couples who use this method should avoid sex from the first days of menses until after the third consecutive day of elevated body temperature.
The Cervical Mucus Method (Billings Method, Ovulation Method)
Hormonal changes during the menstrual cycle affect the appearance and texture of cervical mucus. Immediately after menstrual bleeding, thick, sticky mucus forms a plug at the cervix. The vaginal opening feels dry, and the woman does not notice any signs of mucus. As estrogen levels increase, a thick, sticky mucus appears at the vaginal opening. As ovulation approaches and estrogen levels continue to increase, the mucus becomes clear, stretchy and slippery (the consistency of raw egg whites), and the vaginal opening feels moist. (The thin, watery mucus provides nutrients to sperm cells and protects them from the acidic environment of the vagina. After ovulation, thick mucus returns.) Couples using this method abstain from sex when the woman is menstruating and on alternating days prior to the appearance of cervical mucus. They also abstain from the time the first sticky mucus appears until four days after the last clear, stretchy slippery mucus is observed.
The Symptothermal Method
This method combines several techniques to predict ovulation. It typically includes monitoring cervical mucus and temperature changes and may include other signs of ovulation, such as breast tenderness, back pain, abdominal pain or "heaviness," or light intermenstrual bleeding. Couples who use this method abstain from sex from the first sign or sensation of wet cervical mucus until the woman's body temperature has remained elevated for three days after peak day is observed (last day of clear, stretchy, slippery mucus), or until the fourth day after thin mucus is no longer observed, which comes later.
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