Natural Family Planning
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Efficacy of the Standard Days Method


 

Evidence base of the Standard Days Method

Scientific Basis of the Standard Days Method

 

The SDM is based on reproductive physiology. A woman is fertile 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 up to five days, and the fact that the ovum can be fertilized for up to 24 hours following ovulation.  Ovulation occurs around the mid-point of the menstrual cycle (+/- 3 days). 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.

If a woman has sex 6 or more days before she ovulates, the chance she will get pregnant is virtually zero. If she has 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 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.


To establish the contraceptive efficacy of the Standard Days Method® (SDM), researchers at Georgetown University conducted a prospective multi-center efficacy trial. A total of 478 women, age 18-39 years with self-reported cycles of 26-32 days, were admitted to the study, and followed for up to 13 cycles during method use, contributing 4,305 cycles to the analysis. Subsequently, through operations research SDM was introduced into fourteen program settings in Latin America, Asia and Africa. A total of 1,165 women using SDM were regularly interviewed over a one year period. In the United States SDM is increasingly integrated in punlic and private family planning programs.

Results from Efficacy Trial

The study demonstrated that the SDM is an effective method of family planning. The life-table one-year pregnancy rate was 4.8 with correct use and 12.0 with typical use, demonstrating that method efficacy is comparable to other user-controlled methods currently available.

Approximately 68% of study participants were still using the method at the end of 13 cycles, and 67% two years later.

Irregular cycles (having two cycles out of the 26-32 day range) were the most common reason for leaving the study (28%). Only 4% left the study because they or their partner did not like or trust the method. 45% of women who discontinue the method want to become pregnant.

Click to read more about the efficacy trial of SDM.