Merck Manual

Please confirm that you are a health care professional

honeypot link

Fertility Awareness‒Based Methods of Contraception

(Periodic Abstinence; Rhythm Method)

By

Frances E. Casey

, MD, MPH, Virginia Commonwealth University Medical Center

Medically Reviewed Feb 2022 | Modified Sep 2022
View Patient Education
Topic Resources

Fertility awareness–based methods of contraception involve tracking menstrual cycles and other physiologic signs (eg, cervical mucus) to estimate the timing of a woman's fertile window (the days before, during, and after ovulation when unprotected sexual intercourse may result in pregnancy). Although the ovum can be fertilized for only about 12 hours after ovulation, sperm can fertilize an ovum for up to 5 days after intercourse; as a result, intercourse almost 5 days before ovulation can result in pregnancy. Thus, fertility awareness‒based methods require abstinence from intercourse starting 5 days before ovulation.

Several methods can be used to identify the time of ovulation and thus determine when abstinence is required. They include

  • Standard days (calendar) method: Avoids intercourse on cycle days 8 through 12

  • Two-day (ovulation, or mucus) method: Based on evaluation of cervical mucus

  • Symptothermal method: Uses a combination of basal body temperature, evaluation of cervical mucus, and abstinence during the fertile period

The symptothermal method has a lower pregnancy rate with perfect use than the 2-day method or the standard days method (with or without cyclebeads). However, pregnancy rates with any of these methods are high with typical use, so these methods are not recommended for women who strongly want to avoid pregnancy.

The lactational amenorrhea method is another method, which can be used postpartum if a woman is breastfeeding.

Table

Standard days method

The standard days (calendar) method is based on the calendar (the dates that menses occur) and is appropriate only for women who have regular menses.

Ovulation occurs about 14 days before onset of menses. Thus, the interval of abstinence during the menstrual cycle is determined by subtracting 19 days from the shortest of the previous 12 cycles and 11 days from the longest. For example, if cycles vary between 27 and 29 days, abstinence is required from days 8 through 18 of each cycle. The greater the variance in cycle length, the longer abstinence is required.

Cyclebeads (a string of color-coded beads that represent the days of a menstrual cycle) or other tools (eg, digital menstrual cycle trackers), may be used to help women keep track of their fertile days.

Two-day method

The 2-day (ovulation, or mucus) method is based only on cervical mucus assessment.

Cervical mucus may be absent for a few days after menses. After the mucus reappears, it tends to be cloudy, thick, and inelastic. Shortly before ovulation, the amount of mucus increases, and the mucus becomes thinner, clearer, and more elastic than usual. It resembles raw egg whites and stretches between the fingers.

Intercourse is avoided completely during menses (because mucus cannot be checked). It is permitted during the days when mucus is completely absent, but during these days, intercourse is restricted to every other day (so that semen is not confused with mucus). Intercourse is avoided from the time mucus first appears after menses until 4 days after the amount peaks. Intercourse is permitted without restriction from 4 days after the amount of mucus peaks until menses begin.

A change in cervical mucus indicates ovulation more accurately than body temperature.

Symptothermal method

The symptothermal method combines daily measurement of basal body temperature (which increases after ovulation), cervical mucus assessment, and the standard days method.

Intercourse is avoided from the first day requiring abstinence according to the standard days method until 3 days after the amount of cervical mucus decreases and temperature increases.

Lactational amenorrhea method

The lactational amenorrhea method is based on the natural postpartum infertility that occurs when women breastfeed exclusively (or almost exclusively) and menses has not resumed. The infant's suckling inhibits the release of hormones (gonadotropin-releasing hormone and luteinizing hormone) that are necessary to stimulate ovulation. Without ovulation, pregnancy cannot occur. This method can be 98% effective if the following criteria are met:

  • The infant is < 6 months.

  • Breastfeeding is the primary source of infant feeding (supplementation with formula or solid food or pumping breast milk decreases efficacy).

  • Breastfeeding is done at least every 4 hours during the day and every 6 hours at night.

  • Menses have not resumed (amenorrhea).

View Patient Education
NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
quiz link

Test your knowledge

Take a Quiz! 
iOS ANDROID
iOS ANDROID
iOS ANDROID
TOP