Researchers from the Georgetown University Institute for Reproductive Health (IRH) recently reported on a multi-site effectiveness study of what they call the Standard Day Method (SDM) of family planning.1 SDM is a simple to use and easy to teach natural method of family planning. The SDM is essentially a modified form of Calendar Rhythm that has a "fixed" number of days of fertility for each cycle -- i.e., day 8 to 19. The method is intended for women who have regular cycles between 26 and 32 days in length. The SDM fixed day formula was "retrospectively" and theoretically tested with past data sets and reported in a previous study.2 This study demonstrated that there was a very low probability of pregnancy outside of the projected 11-day period of fertility. The highest day of probability of pregnancy from an act of intercourse was only 0.007 during this extended window of fertility.
The SDM was prospectively tested for its effectiveness in helping couples avoid pregnancy among 478 women from 5 different sites in three developing countries (the Philippines, Peru, and Guatemala). The participants were between 18-39 years old, had menstrual cycles between 26-32 days in length, and were willing to avoid intercourse for 12 consecutive days each cycle. Each study site had 5-10 trained health workers who instructed the participants in the SDM and who contacted them monthly for the length of the study. Participants were also asked to keep a calendar to record the beginning and end of their cycles, acts of intercourse, and any other method used to avoid pregnancy (e.g., condoms or withdrawal).
The SDM uses a colored bead necklace system (called CycleBeads) that indicate the beginning (a red bead) of the cycle, followed by 6 brown beads of infertility, then 12 days of fixed fertility (white beads) and then 13 more days of infertility (with brown beads). The CycleBead system also has a dark brown bead for day 27 that indicates to the user that if they start their menses before that date they should contact their "provider." If they reach the last bead (day 32) and still have not started their menses they were also asked to contact their provider. The marker beads helped the user to know whether they fell into the 26-32 day cycle length to which this CycleBead system applies. The rules for the CycleBead system are simple, i.e., "on brown bead days you can have intercourse with very low probability of pregnancy", and "on white bead days you can get pregnant. Avoid unprotected intercourse to prevent a pregnancy."
The 478 participants had a mean age of 29.4 years, most (90%) had at least a primary level education, 98.9% had children (mean 2.5), and almost 80% were Catholic. One third of the women were breastfeeding on admission to the study, but had at least three menstrual cycles since the last birth. Of the 478 women who entered the study, 46% completed 13 cycles of use. Most (28%) of the women who discontinued did so because they had 2 cycles out of the 26-32 day range.
The 478 women generated 4,035 cycles of data of which 92% had correct method use (i.e., no intercourse on the white bead fertile days of 8-19), 5% of the cycles had intercourse with condoms or withdrawal during the fertile phase, and 3% had intercourse during the fertile phase. Only 43 of the 478 women became pregnant with use of the CycleBead system. Of these 43, 15 conceived outside of the method defined fertile phase. Most (65%) of the pregnancies occurred in cycles in which the participant reported intercourse during the 8-19 day fertile phase. Using life table analysis the Georgetown University researchers were able to calculate a 1-year pregnancy rate of 4.8 (95%; CI 2.33-7.11) with perfect use and a pregnancy rate of 12 (88%; CI 8.74-15.33) with typical use of the method (that involved all cycles and all pregnancies).
The authors concluded that this study demonstrated that the SDM with use of the CycleBead system was an effective method of family planning that is comparable to the male condom and significantly better than other barrier methods. They also concluded that this method is acceptable to couples in a wide range of settings and would be a valuable addition to reproductive health providers and other community services programs.
Strengths of this prospective effectiveness study were that the researchers recommended guidelines for effectiveness studies and did not include data from cycles that did not have any intercourse recorded. Further, they enrolled participants in the study when they first began using the system to avoid pregnancy (i.e., they did not have a learning phase with abstinence that typically occurs with NFP effectiveness studies). A potential limitation is that they relied on self-reporting of intercourse and the participants might have under-reported intercourse during the fertile phase. A caveat in interpreting the effectiveness of the SDM based on the study results is that there were monthly follow-ups and contacts of the participants by the health workers. This monthly contact might have increased the correct use of the method. It remains to be seen how effective this method would be without monthly inperson follow-ups.
The results of this study are similar to those of an earlier (2000) study using a fixed day method of fertility and a necklace bead system among the Mayan population in Guatemala.3 The Guatemala study used a slightly more liberal formula for the fixed days of fertility than the SDM (i.e., day 9-19 instead of day 8-19) and resulted in a typical use pregnancy rate of 11%.
In the early 1980s, the JPH Corporation was selling (for $2) a "pure and simple" Fertility Finder. The Fertility Finder was a small credit card size card that provided the user a simple way of determining the fertile days of a cycle by month of the year. The card indicated that fertility begins on the 10th day of the woman's cycle and ends on the 18th day. The Fertility Finder was to be used for cycles in the 26-33 day range and was based on data from the University of London and reported in a 1969 issue of Population Studies.4 However, there never was a prospective efficacy study of the Fertility Finder. I commend the researchers at Georgetown University Institute for Reproductive Health for doing a careful, well designed and systematic study of the SDM. A multi-site, prospective effectiveness study of a new method of family planning is a very difficult task. I look forward to further findings from this study. (RJF)
1 Arevalo, M., Jennings, V., and Sinai, I. Efficacy of a new method of family planning: the Standard Day Method. Contraception. 65 (2002): 333-338. [Back]
2 Arevalo, M., Sinai, I., & Jennings, V. A fixed formula to define the fertile window of the menstrual cycle as the basis of a simple method of Natural Family Planning. Contraception. 60 (1999): 357-60. [Back]
3 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 (August, 2000): 131-136. [Back]
4 James, W.H. The mathematics of the menstrual cycle. Population Studies. 22 (November, 1968): 409-413. [Back]