SDM Implementation Guidelines

About the SDM

What is the SDM?

The SDM is a simple and effective fertility awareness-based method of family planning developed through scientific analysis of the fertile time in the woman’s menstrual cycle. The SDM is based on the fact that there is an identifiable “fertile window” during the woman’s menstrual cycle—several days before ovulation and about 1 day after—when she can become pregnant. To prevent pregnancy, users avoid unprotected intercourse on days 8 to 19 of the cycle—a formula based on computer analysis of 7,500 menstrual cycles [1]. Some couples choose to abstain during the fertile days while others prefer to use a barrier method, usually condoms. A set of colored beads, called CycleBeads®, facilitate provision and use of the SDM by helping a woman track her cycle days, know which days she is fertile, and monitor her cycle lengths.

The SDM is a modern, scientific method which provides two couple years of protection (CYP) per user [2]. Although it is a relatively new method, it is now being used in more than 21 countries around the world. Ministries of health, non-governmental organizations, international private voluntary organizations, and community development groups are including it in their policies, norms, and services. The method has been incorporated into guidance documents for contraceptive use such as the WHO’s Medical Eligibility Criteria for Contraceptive Use, and Contraceptive Technology 18th Edition, as well as the policies and norms of numerous goverments and private sectors programs.

How was the SDM developed?

The SDM was developed by the Institute for Reproductive Health, Georgetown University with support from the U.S. Agency for International Development. To develop this method, researchers:

  • identified days 8 to 19 as the likely fertile window, taking into account human reproductive physiology, such as viable lifespan of the gamete, the probability of becoming pregnant on different days relative to ovulation, and the probability of ovulation on different days of the cycle relative to the mid-point day.
  • then a computer model was designed to assess the efficacy of the 8 to 19 fertility windown and to identify for whom it would be appropriate. The model was applied to menstrual cycle data from a number of published studies and a large data set from the World Health Organization. The analysis confirmed that avoiding unprotected intercourse on days 8 through 19 provided maximum protection for women with menstrual cycles between 26 and 32 days long (78% of cycles are in this range), while minimizing the number of days to avoid unprotected intercourse.
  • A clinical trial was conducted to determine its effectiveness in actual use. The study included nearly 500 women in three countries – Bolivia, Peru, and the Philippines – who used the method for up to one year. The study followed internationally recognized procedures used in efficacy studies for all modern family planning methods.
  • Follow-up studies conducted in the clinical trial sites looked at method continuation following the completion of this trial.
  • Operations research studies were conducted in sites where the SDM was introduced. These studies examined acceptability of the method to providers and users, the feasibility of offering the method, and its effectiveness in typical service delivery settings.

What is the scientific basis of the SDM?

The SDM is based on reproductive physiology. A woman is fertile approximately five days before ovulation plus the day of ovulation. This is because of the life span of the sperm, which remain viable in the woman’s reproductive tract for approximately five days, and the fact that the ovum can be fertilized for up to 24 hours following ovulation.

If a woman has unprotected sex 6 or more days before she ovulates, the chance she will get pregnant is virtually zero. If she has unprotected sex 5 days before she ovulates, her probability of pregnancy is about 5%. Then, her probability of pregnancy rises steadily until the two days prior to ovulation. If she has unprotected sex on either of these two days, she has a 25-30% chance of becoming pregnant.

From that point, the probability of pregnancy declines rapidly. By 12-24 hours after she ovulates, a woman is no longer able to get pregnant during that cycle. [3]

Probability of Pregnancy from
Intercourse on Days Relative to Ovulation

The timing of ovulation during the menstrual cycle also is important for the SDM. Ovulation occurs around the mid-point of the menstrual cycle particularly for regularly-cycling women. In approximately 89% of cycles, ovulation occurs within +/- 3 of the midpoint day. Thus, a woman’s fertile “window” (days in the menstrual cycle when she can get pregnant) begins as early as five days prior to ovulation and lasts up to 24 hours after ovulation.

How effective is the SDM?

To determine the contraceptive efficacy of the SDM, a prospective, multi-center efficacy study was conducted in Bolivia, Peru, and the Philippines among 478 women 18 to 39 years of age.

The results of the study found that, for women with cycles between 26 and 32 days long, the SDM is more than 95% effective with correct use and more than 88% effective with typical use [4] (typical use calculations include women who had unprotected intercourse during the fertile days as well as those who did not). This is similar to the efficacy of most other user-dependent methods.

Contraceptive Failure of User-Directed Methods
% of women who became pregnant
during 1st year of use
Correct Use
Typical Use
No Method
Standard Days Method

Adapted from Contraceptive Technology, 18th Edition, 2004.

These, the SDM provides significant protection against unplanned pregnancies and is well accepted by couples in a wide range of settings. The method was used correctly in about 97% of the cycles. Similar typical-user failure rates have been reported in other studies conducted in several countries. [5]

How is the SDM used?

In many programs the SDM is used in conjunction with CycleBeads, a visual tool that helps women use the SDM by keeping track of their cycle days, identify whether or not they are fertile on that day, and monitor cycle length.

Indications for Using CycleBeads

  • To track her fertile days, the woman moves a rubber ring one bead every day. On the day she starts her period, she moves the ring to the red bead and marks that day on her calendar. To prevent pregnancy, she avoids unprotected sex when the ring is on a white bead day. On all brown-bead days, pregnancy is very unlikely. On the day she starts her next period, she skips over any remaining brown beads, puts the ring on the red bead, and begins a new cycle.
  • To monitor her cycle length, the woman knows that if her period starts before moving the ring to the darker brown bead her cycle is shorter than 26 days. If she doesn’t start her period by the day after moving the ring to the last brown bead, her cycle is longer than 32 days. If she has a cycle shorter than 26 or longer than 32 days more than once in a year, the SDM will not be effective for her, and she should be encouraged to use another method.

Who can use the SDM?

The SDM is appropriate for many women but, like all methods of family planning, it is not appropriate for all who may want to use it. According to the World Health Organization’s “Medical Eligibility Criteria for Contraceptive Use” (2004), the SDM does not have any negative effect on a women's health. [6]

As noted previously, to use the SDM successfully, women should have regular menstrual cycles between 26 and 32 days long. Because successful use of the SDM involves using condoms or not having sex on days 8 to 19 of the cycle, the woman's partner also needs to be involved. Women who have more than one cycle outside this range in a year should not use the SDM to prevent pregnancy, since the method would be less effective for them.

Like most family planning methods, other than condoms, the SDM does not protect against STIs and HIV/AIDS.

Is the SDM appropriate for young women and newly married couples?

Research shows that young women and newly married couples also can effectively use the SDM. The research found that younger women have more frequent sexual intercourse, and they may have it more frequently during their fertile days, but they use more back-up protection on those days than older women. As a result, there was no statistical difference in the pregnancy rates among young women versus older women. What is most relevant for effective use of the SDM is that women have regular cycles and that they are able to communicate with their partners about how to handle the fertile days. Younger girls may have very irregular cycles. But by 3 to 4 years after the first menstruation, most adolescents have fairly regular cycles at which time the SDM may be appropriate for them, if they meet the regular screening criteria [7].

Do women need to be educated or literate to use the SDM?

SDM studies conducted in Latin America, Asia and Africa demonstrate that women with very little education and those who cannot read or write can use the method as effectively as highly educated women. However, they may require specially tailored materials and more counseling time [8].

Copyright 2006 Institute for Reproductive Health