Original research articleEfficacy of a new method of family planning: the Standard Days Method☆
Introduction
A couple wanting to avoid or achieve pregnancy by timing intercourse needs to know when during her menstrual cycle the woman is most likely to become pregnant. They can do so by using a fertility awareness-based family planning method. The fertile window of the woman’s menstrual cycle consists of approximately 6 days—the 5 days before ovulation and the day of ovulation, with variable probabilities of pregnancy for each day [1], [2]. However, the timing of ovulation is variable both among women and across cycles of the same woman, with some women experiencing much greater variability than others [3]. A fertility awareness-based method that takes into account this variability could be a viable option for many couples. The Institute for Reproductive Health, Georgetown University, proposed a fixed formula in which women who typically have menstrual cycles of 26 to 32 days consider themselves fertile during Days 8 through 19 (12 days) of their cycles. To prevent unplanned pregnancy, they avoid unprotected intercourse on those days [4].
Ideally, a woman using a fertility awareness-based method should be able to identify the 6 days of her fertile window, with neither “false positives” (i.e., days identified as fertile that actually are infertile), nor “false negatives” (i.e., days identified as infertile that actually are fertile) [5]. The technology necessary for this degree of accuracy, however, is not widely available or affordable, especially in developing countries. Balancing the need to provide effective protection from unplanned pregnancy while restricting the identified fertile period to as few days as possible, we developed the Standard Days Method (SDM), in which a woman considers herself potentially fertile on Days 8 through 19 of her menstrual cycle. If she does not want to become pregnant, she avoids unprotected intercourse on those days.
To develop the SDM, we applied various formulae (i.e., various numbers of days and various sets of days) to over 7500 menstrual cycles in an existing data set from the World Health Organization (WHO) [6]. The goal was to determine which formula provided the best balance between length of the identified fertile period and efficacy in avoiding unplanned pregnancy. To accomplish this, we developed a computer simulation that took into account the variable probability of pregnancy on different cycle days before and including the probable day of ovulation as well as the variable probability of ovulation occurring on different cycle days.1 The 8 through 19 formula provided maximum protection while minimizing the number of days of avoiding unprotected intercourse. We estimated that if women with cycles ranging 26 to 32 days had used the 8 through 19 formula and avoided unprotected intercourse on those days, the highest probability of pregnancy on any given day was only 0.007.
We then estimated that the method would be almost as effective for women who typically have cycles within the 26 through 32 day range but occasionally (no more than twice in a 12-month period) have a shorter or longer cycle. However, the 8 through 19 formula would be less effective for women who consistently have cycles shorter than 26 days or longer than 32 days. Nonetheless, even when all women and all cycles regardless of length were included in the computer simulation, the highest probability of pregnancy/intercourse on any given day was still only 0.011.
In designing this efficacy study, we followed the guidelines recommended by Trussell and Kost [7]. Data collection instruments, participant enrollment, and pregnancy definition were all influenced by those recommendations. Their guidelines also affected the way we analyzed the data and, thus the results presented in this article.
Section snippets
Materials and methods
A prospective, non-randomized, multi-center study to test the efficacy of the SDM was conducted among culturally diverse populations. Participants were enrolled from five sites in Bolivia (Trinidad), Peru (Juliaca and Lima), and the Philippines (La Trinidad and Tuba).
Results
A total of 478 women were admitted into the trial, with a mean age of 29.4 years. Women in the study were drawn from urban, mixed urban/rural and rural sites. Lima was the largest city; study participants from La Trinidad (the Philippines), Trinidad (Bolivia), and Juliaca (Peru) lived in a variety of mixed urban/rural settings in these smaller cities; Tuba (the Philippines) was a rural site.
Participants’ educational levels were relatively high: more than 90% of women had completed primary
Discussion
With only 43 women of 478 in our study becoming pregnant, it appears that the SDM is effective in preventing unplanned pregnancies. As shown in Table 5, efficacy of the SDM is comparable to that of male condoms and is significantly better than that of other barrier methods (female condom, diaphragm, cervical cap, or spermicides) [9].
The finding that the method was used correctly in most cycles (i.e. that couples avoided unprotected intercourse during the entire fertile period as identified by
Conclusion
This efficacy trial demonstrated that the SDM is an effective method of family planning. With a first year pregnancy rate of less than 5% with correct use, it is comparable to other user-controlled methods currently available through reproductive health and other programs. The study also has shown that clients are able to learn the method and to use it successfully to avoid unplanned pregnancy. The SDM offers a valuable addition to the services that reproductive health and other programs can
Acknowledgments
The authors are particularly grateful to our field collaborators: Dr. Saleg Eid, Catholic Relief Services, Bolivia; Dr. German Coaguila and Pilar Lacerna of Centro de Informacion Educacion y Servicios, Bolivia; Dr. Irma Ramos, CARE, Peru; Beth Yeager, Instituto de Investigacion Nutricional, Peru; and Betty Toledo and Mitos Rivera, Institute for Reproductive Health, Philippines. The Department of Health in Benguet, Philippines, the Ministry of Health in Juliaca, Peru, as well as the providers,
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Support for conceptualizing the SDM, implementing the effectiveness study, and preparing this article was provided by the Institute for Reproductive Health, Department of Obstetrics and Gynecology at Georgetown University, Washington, DC, which is funded under a cooperative agreement HRN-A-00-97-11100-00 with the United States Agency for International Development (USAID).