NFP Science Seeking Innovation

In addition to the well-established Natural Family Planning methods that are based on the observation and interpretation of cervical mucus, the basal body temperature, cervical changes, other symptoms, and (as in the Sympto-Hormonal methods), the use of fertility devices, some researchers continue to look for approaches that do not rely entirely on human observation and interpretation. These approaches provide guidelines based on research of menstrual cycles.

Researchers at the Institute for Reproductive Health at Georgetown University (Washington, DC) have developed two methods of NFP: the Standard Days Method and the TwoDay Method.

The Standard Days Method (SDM) makes use of CycleBeads (a plastic ring of colored beads) to track the fertility of the woman’s menstrual cycle. The colors of the beads indicate times of menstruation, fertility, and infertility. A small black ring can be moved forward around the beads to indicate the current day of the woman's cycle. Day one of each new cycle begins with menstruation.

The SDM is based on research of hundreds of women’s menstrual cycles. The SDM provides a formula for women who have cycles between 26 and 32 days in length. The days of the cycle that are considered fertile are days 8 through 19. If a woman has two cycles longer than 32 days or shorter than 26 days, she is advised to use another method of NFP.

When used correctly the SDM is 95% effective for pregnancy avoidance. When not used correctly, the SDM is 87% effective for avoiding pregnancy. The SDM is also effective for attempting conception. When the married couple wishes to attempt conception, they would target conjugal relations to the days that have the specific color on the bead for the fertile time.

The second method developed by IRH is TwoDay method. it is based on research about cervical mucus. It makes use of two simple questions:

  • Did I notice cervical secretions today?

  • Did I notice cervical secretions yesterday?

If the woman answers “No” to both questions, she can consider herself infertile. If she answers "Yes" to even one of the questions, she should consider herself fertile. Married couples would then plan accordingly if they wish to attempt or postpone conception.

When used correctly, the TwoDay method is over 96% effective for avoiding pregnancy. And, it is very effective for attempting conception when conjugal relations are targeted on the days of noticed cervical secretions.

The above two methods are easy to teach and easy to learn. An important consideration to this approach, however, is that married couple should be informed that the SDM and the TwoDay Method do not provide specific information about their fertility. Married couples should be informed about those methods of NFP that teach couples about their combined fertility. This is critical since some couples may prefer to learn about their fertility rather than follow standard guidelines. In addition, the NFP methods which teach the observation, interpretation, and charting of the woman's fertile signs can provide invaluable information that may have an impact on the woman's health.


Finally, it should be noted that the above methods have been developed for the general public. If a faith-based NFP teacher wants to provide the SDM or TwoDay Method, it will be important to ask for the "faith-based" materials. 

Select Articles

(See the NFP Science Bibliography for a list of foundational and current research.)

Arevalo, M., Jennings, V., Sinai, I. "Efficacy of a new method of family planning: the Standard Day Method." Contraception 65 (2002): 333-338.

Arevalo, M., Jennings,V., Nikula,M., Sinai, I. "Efficacy of the new TwoDay Method of family planning." Fertility and Sterility 82 (2004): 885-892.

Burkhart, M. C., de Mazariegos, L., Salazar, S., Lamprecht, V. M. "Effectiveness of a standard-rule method of calendar rhythm among Mayan couples in Guatemala." International Family Planning Perspectives 26 (2000): 131-136

Jennings,V., Sinai, I., Sacieta, L., Lundgren, R. "TwoDay Method: a quick-start approach." Contraception 84 (2011): 144-149.


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