At its core, Natural Family Planning (NFP) is really learning about this language of the sexual powers by observing, recording and interpreting the bodily signs of human fertility. In other words, NFP is fertility awareness, the knowledge of a couple’s fertility, and is a means of reading the body’s signs of fertility and infertility.
How NFP Works
Natural Family Planning uses the natural increase and decrease in fertility built into a woman’s menstrual cycle to increase or decrease the possibility of conception. There are several different modern effective methods of NFP. Each identifies the most fertile time in a woman’s cycle and requires the couple to abstain from sexual intercourse during that time, if they wish to avoid conception.
The Billings Ovulation Method uses observations about changes in a woman’s body during her cycle to determine the time when she is most fertile.
The Creighton Model is a modified version of the Billings Ovulation Method.
The Sympto-Thermal Method relies on observations as well as changes in body temperature. It is more effective and more complex than observation-only methods.
The Standard Days Method is a new method of NFP developed by the Institute for Reproductive Health at Georgetown University. It does not use observations or temperature. It is an updated calendar method. The couple abstain from sexual intercourse on days 8 through 19 of each cycle; cycles begin on the first day of her period, and cycles must be from 26 to 32 days in length.
The Two-Day Method, also developed at Georgetown, uses observations and a simple two-day rule. It is easier to learn than the Billings or Creighton methods, but somewhat less effective.
Ecological Breast-Feeding or the Lactational Amenorrhea Method is only used by mothers who are breast-feeding a newborn. It allows new mothers to delay the return of ovulation and their periods for weeks or months after a birth. It is the only NFP method that does not require periodic abstinence.
Effectiveness of NFP
The effectiveness of any method of NFP varies from one couple to another.
All NFP methods are significantly less effective for couples who do not follow the method closely.
Older couples are generally less fertile than younger couples.
All NFP effectiveness percentages refer to couples who practice the method correctly and strictly. Different studies show different degrees of effectiveness; there is no single exact number to cite. A 95% method effectiveness would mean that 5 out of 100 women, practicing the method correctly for one year, will get pregnant. Individual effectiveness varies.
The Sympto-Thermal Method: ~99% effective (reference)
The Creighton Method: >98% effective (reference)
The Billings Method: >97% effective (reference)
Two-Day Method: ~96% (reference)
Standard Days Method: ~95% (reference)
Ecological Breast-Feeding (LAM): ~94% effective (reference)
Sources:
http://www.natural-family-planning.info/
http://www.ccli.org/nfp/