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Standard Days Method

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SDM is a method based on fertility awareness; users must avoid unprotected sexual intercourse on days 8–19 of the menstrual cycle (280). Approximately 5 out of 100 women become pregnant in the first year of use with perfect (i.e., correct and consistent) use of SDM (280); effectiveness based on typical use is not available for this method but is expected to be lower than that for perfect use. SDM is reversible and can be used by women of all ages. SDM does not protect against STDs; consistent and correct use of male latex condoms reduces the risk for STDs, including HIV.

Use of SDM Among Women with Various Durations of the Menstrual Cycle

Menstrual Cycles of 26–32 Days

  • The woman may use the method.
  • Provide a barrier method of contraception for protection on days 8–19 if she wants one.
  • If she has unprotected sexual intercourse during days 8–19, consider the use of emergency contraception if appropriate.

Two or More Menstrual Cycles of <26 or >32 Days Within Any 1 Year of SDM Use

  • Advise the woman that the method might not be appropriate for her because of a higher risk for pregnancy. Help her consider another method.

Comments and Evidence Summary. The probability of pregnancy is increased when the menstrual cycle is outside the range of 26–32 days, even if unprotected sexual intercourse is avoided on days 8–19. A study of 7,600 menstrual cycles, including information on cycle length and signs of ovulation, concluded that the theoretical effectiveness of SDM is greatest for women with cycles of 26–32 days, that the method is still effective for women who occasionally have a cycle outside this range, and that it is less effective for women who consistently have cycles outside this range. Information from daily hormonal measurements shows that the timing of the 6-day fertile window varies greatly, even among women with regular cycles (21,281,282).

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