Natural family planning (NFP) is a way of avoiding or achieving a pregnancy without the use of drugs or devices. NFP is a way of life in which a couple recognizes their days of fertility and infertility, and together they decide if they will engage in conjugal love or abstain. There are many variations of NFP methods that can be placed under five broad categories: Sympto-Thermal, Mucus, Sympto-Hormonal, Temperature, and Rhythm.
The Sympto-Thermal Methods (1950s) are based on the changes in three physical signs experienced by the woman: cervical mucus, temperature and the position, texture, and opening/closing of the cervix.
The Mucus Methods (1960s) are based on the recognition of a specific type of cervical mucus present before ovulation and experienced at the vulva. Pregnancy cannot occur without fertile mucus. In addition to this primary sign of fertility, clients learn to recognize other external signs of fertility.
The Sympto Hormonal Methods (1990s) are based on the detection of specific levels of reproductive hormones utilizing a fertility monitor (or other device) alone or in conjunction with another sign of fertility such as mucus or temperature.
The Temperature Method (1940s) is based on the medical fact that a rise of the woman's basal body temperature (BBT) occurs a few days before or after ovulation.
Rhythm (1930s) is the oldest known NFP method. It is based on the fact that menstruation occurs about fourteen days after ovulation. Rhythm is based on a woman's history of past regular cycles. Rhythm is 75 to 85% effective in avoiding a pregnancy. There are several versions of the Rhythm Method suggesting different numbers for calculating the fertile time of the cycle. The Rhythm Method is effective when cycles are consistently regular.
The Sympto-Thermal, Mucus, Sympto-Hormonal and Temperature NFP methods are up to 99% method effective in avoiding a pregnancy and are based on signs of fertility and infertility that occur on a daily basis in the present cycle–not in past cycles. The Rhythm method is 75-85% effective in avoiding a pregnancy as it relies on predicting the fertile time of a cycle assuming the current and future cycles will be the same as past cycles.