In general, natural family planning (NFP) involves recognizing the natural rhythms in a woman's fertility. Depending on their goals, couples may choose to time sexual intercourse so that it falls during the infertile phase (to avoid pregnancy) or the fertile phase (to achieve it). NFP is the sole method of contraception permitted by the Catholic Church and has been given the nickname Vatican Roulette.

The calendar method, also known as the "rhythm method", relies solely on counting days in order to estimate the onset of a woman's fertile period. There are also additional, more reliable forms of NFP, such as the basal body temperature method, the cervical mucus method, and the symptothermal method. In addition, mothers of newborns can delay the return of their menstrual cycle (and thus, their fertility) by using the lactational amenorrhea method (LAM).

As well as the religious imperative of many couples using the method, supporters typically advocate NFP because it is free (apart from the purchase of a thermometer and charts), natural (introducing no chemicals into the body nor artificial devices to modify the sex act), and the only family planning method that involves both the man and the woman equally (since the two must communicate with each other in order to be aware of the woman's cycle and weigh their feelings about having children). For detractors, however, the latter "benefit" is in fact regarded as a disadvantage.

NFP methods do require regular, consistent effort to determine when a couple's chance of fertility is low. For many women, the times of high fertility coincide with the time of highest libido. The "scheduling" of sex required can be inconvenient for partners who do not live together and are unwilling to abstain or use non-procreative forms of sex when they are able to spend time together. For these reasons, other methods are more popular than NFP among large sections of society.

While the calendar method (by itself) is not the most reliable form of NFP, over a term of one year, some studies (by Planned Parenthood and, the US Food and Drug Administration) estimate that less than 25% of women in sexual relationships who use the calendar method precisely will get pregnant, while others by NFP proponents estimate the pregnancy rate at only about 9%. Even the pessimistic estimate is much lower than chance (85% of women not using any contraceptive methods will become pregnant in one year), while even the optimistic one is considerably higher than optimally-used hormonal contraceptives. Numerous studies of couples in North America and Europe using the sympto-thermal method of NFP have demonstrated 99% effectiveness at avoiding pregnancy.

In most women the menstrual cycle lasts between 24 and 32 days. It starts with a menstrual bleeding. Ovulation takes place at some time between day 12 and day 18. Ova die if not fertilized within 24 hours of ovulation. Spermatozoa are able to fertilize an ovum for a period of about three days after they have been ejaculated, although exceptional cases of fertilization almost one week after intercourse have also been reported.

The period from the start of menstruation to ovulation lasts between 12 and 18 days, depending on the length of the cycle (24 to 32 days). Eliminating the seven days during which sperm can survive in a woman's body, this leaves a first infertile period of five to eleven days from the beginning of menstruation. (Of course, during the first four or five days of this period, the woman will be menstruating.) The second infertile period occurs after ovulation. The time of ovulation can vary, especially if the cycle is not completely regular. Thus, if the couple wished to avoid conception, they must abstain from intercourse for the first four days after the expected time of ovulation as well. Thus, the second infertile period starts on day 16 after the beginning of menstruation in a woman with a 24-day cycle, and on day 22 in a woman with a 32-day cycle. The woman can then be considered infertile until the next menstruation starts.

Observational Methods

NFP methods which not only keep track of the woman's menstrual cycle, but also make observations about the statue of a woman's body, offer additional information for couples to use when considering having intercourse.

The basal body temperature method is based on the fact that two or three days after ovulation, hormonal changes cause a rise in body temperature between 0.3 and 0.9C (0.5 and 1.6°F) that lasts at least until the next menstruation.

The cervical mucus method (or Billings method, or Billings ovulation method) involves checking the texture of the mucus secreted by the cervix. When a woman is not fertile, the mucus is light or sticky. During the day before and the day of ovulation, (the most fertile time period), the increase in estrogen levels causes more copious mucus that is clear and slippery.

The symptothermal method combines the techniques discussed above. Some women may also check the position and feel of their cervix, and note breast tenderness or ovulatory pain (mittelschmerz), the lower abdominal pain or cramping some women feel around the time of ovulation.

The lactational amenorrhea method (LAM) of contraception makes use of the natural infertility which occurs through breastfeeding. It is 99% effective during the first six months postpartum in about 90% of women who:

  • Breastfeed their infants exclusively
  • Pacify their infants at the breast, not with pacifiers or bottles
  • Breastfeed often
  • Sleep with their infants
  • Are not separated from their infants for more than three hours a day
  • Take daily naps with their infants

Obviously, this method is only practical for women whose lifestyles allow for it.

See also: Pearl Index

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