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 .
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 .
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
- 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
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
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. 
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
(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
Failure of User-Directed Methods
% of women who became pregnant
during 1st year of use
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. 
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. 
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
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 .
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 .