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2591 pages added, reviewed or updated during the last month (last updated: 16/4/2021)

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rhythm method of natural family planning

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  • Rhythm Method (RM)
    • introduced in the 1920s before the availability of hormonal methods of contraception
    • effectiveness of RM has never been precisely determined
    • one type of traditional RM is practiced by counting days in a cycle, with the beginning of menstruation being day 1 for each cycle
      • days 12 to 19 (inclusive) are considered fertile
      • the difference between the longest and shortest of the previous 8 to 12 cycles are subsequently added as additional fertile days at the beginning of the fertile time
      • a meta-analysis has reported total unplanned pregnancy rates of 15% to 18.3%
      • effective use of the RM is hindered by events that affect the length and regularity of the menstrual cycle, including the use of hormonal contraceptives, recent pregnancies or childbirth, breastfeeding, menarche or menopause, inherent cycle variation, or illness
        • more pregnancies result when cycles are irregular
      • RM typically overestimates the fertile period, and accurate history of the menstrual cycles of the previous 8 to 12 months is necessary for use of the method. Without data about past cycles it is not considered reliable for avoiding pregnancy

    • one modern user-friendly calendar method is the standard day method (SDM)
      • applicable for women with cycles consistently between 26 and 32 days (inclusive)
      • differs from previous calendar methods in that historical data are not needed to calculate the fertile window
      • days 8 to 19 (inclusive) are considered fertile for all users of this method. Two or more cycles outside of the 26- to 32-day range within 1 year contraindicate SDM use
      • color-coded cycle beads, essential to SDM practice, help with tracking fertile and infertile days
      • use of SDM is also limited during variable menstrual cycles


Last reviewed 01/2018