Forms of family planning based on a woman's natural cycle of fertility are called “natural family planning” (NFP). They can be used to prevent pregnancy or optimize the possibility of getting pregnant without interventions which counteract the natural functions of the human body.

There are several types or methods of natural family planning, all of which rely on determining a woman’s regular fertile and infertile periods and deciding whether to have or not have sexual intercourse during those periods. All of these methods are different from, and more effective than, previous methods such as the "rhythm" or "calendar" methods.

• Cervical Mucus Methods such as the Creighton Model or the Billings
Ovulation Method are based on charting the presence or consistency of
cervical mucus to determine fertility.

• Sympto-Thermal Methods such as those recommended by the
Couple to Couple League and Natural Family Planning International use
a combination of cervical mucus, basal body temperature, and the
position of the cervix to determine fertility.

• The Sympto-Hormonal Method, sometimes called The Marquette
Model, combines the observation of cervical mucus with an electronic
fertility monitor which measures a woman’s reproductive hormones in
order to determine fertility.
These methods of natural family planning can be used by couples seeking to prevent or space pregnancies as well as couples who are having difficulty getting pregnant, by women who are breastfeeding, are peri-menopausal, have regular or irregular cycles, or have medical conditions such as hormone imbalance or PMS.

Natural family planning is endorsed by the Catholic Church and other religious groups, as well as many individuals and groups concerned about the health of women, because it does not use chemicals, drugs, physical devices or medical procedures which frustrate the inherent purposes of sexual intercourse or have dangerous side-effects.

Couples who use natural family planning do so for a variety of reasons, in addition to the moral issues raised by the Church. Many couples use natural family planning because it is safe, drug-free, non-invasive, and poses no long-term health risks; because it is affordable and simple to use; and because it can be used both to get pregnant or to postpone pregnancy. In addition, using natural family planning makes both parents co-responsible for conceiving children, and strengthens a couples’ relationship by teaching them to communicate honestly and comfortably about the most intimate personal, physical, sexual and spiritual aspects of their lives.

Modern methods of natural family planning are extremely effective when used correctly. Success rates for the methods outlined above range from 96.8 to 99.6 percent. (A frequently cited study which rated "natural family planning" methods only 76 percent effective included older and less reliable methods such as the "rhythm" and calendar methods.)

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> Natural Family Planning (Archdiocese of Dubuque)