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Fertility Awareness-Based Methods of Contraception

(Rhythm Method; Periodic Abstinence)


Frances E. Casey

, MD, MPH, Virginia Commonwealth University Medical Center

Reviewed/Revised Aug 2023
Topic Resources

Fertility awareness methods involve identifying which days a woman is likely to be fertile during her menstrual cycle Menstrual Cycle Menstruation is the shedding of the lining of the uterus (endometrium) accompanied by bleeding. It occurs in approximately monthly cycles throughout a woman's reproductive life, except during... read more . This information can be used to increase the chance of becoming pregnant or to prevent pregnancy.

When used to prevent pregnancy, these methods depend on abstinence from sexual intercourse during the woman’s fertile time of the month. In most women, the ovary releases an egg about 14 days before the start of a menstrual period. Although the unfertilized egg survives only about 12 hours, sperm can survive for as long as 5 days after intercourse. Consequently, fertilization can result from intercourse that occurred up to 5 days before ovulation (when the egg is released), as well as at ovulation.

There are several fertility awareness methods:

  • Calendar method: Sexual intercourse is avoided on days 8 through 12 of the menstrual cycle.

  • Mucus method: This method is based on the woman's observation of secretions (cervical mucus) from the vagina,

  • Symptothermal method: A combination of body temperature at rest (basal body temperature), observation of cervical mucus, and use of the calendar method.

Each method tries to estimate when ovulation occurs and thus determine which days the woman is fertile. These methods require training, effort, and many steps to be effective.

Fewer women become pregnant with perfect use of the symptothermal method than with the calendar or mucus methods. However, the percentage of women who become pregnant with typical use of any of these methods is high. Thus, these methods are not recommended for women who strongly want to avoid pregnancy.


Comparison of Fertility Awareness‒Based Methods of Contraception


Percentage of Women Who Become Pregnant During First Year of Use With Perfect Use

Percentage of Women Who Become Pregnant During First Year of Use With Typical Use

Calendar method



Mucus method




< 1%


The lactational amenorrhea method is another method. It can be used after delivery of a baby if a woman is breastfeeding. It can be very effective under certain circumstances.

Did You Know...

  • Sperm can survive (and fertilize an egg) up to 5 days after sexual intercourse.

Calendar method

The calendar method (also called the standard days method) can be used only by women who have regular menstrual periods. Women may use cyclebeads or another tool (such as a menstrual cycle tracker app) to help them keep track of their fertile days. These beads are color-coded, and each bead represents a day of the cycle. To use the tracker, women enter the date their last period began, the length of time it lasted, and the average length of their cycle. This information helps women identify when ovulation is likely to occur—usually on the 14th day of the menstrual cycle.

To calculate when to abstain from intercourse, a woman subtracts 18 days from the shortest and 11 days from the longest of her previous 12 menstrual cycles. For example, if cycles last from 26 to 29 days, she must abstain from intercourse from day 8 (26 minus 18) through day 18 (29 minus 11) of each cycle. The more the cycle length varies, the longer a woman must abstain. The day that a menstrual period begins is considered day 1.

Mucus method

The mucus method is also called the 2-day (or ovulation) method. The woman determines her fertile period by observing secretions (cervical mucus) from the vagina, if possible, several times every day, starting the day after a menstrual period stops. Women should record their observations.

Mucus usually has the following pattern during the menstrual cycle:

  • There may be no mucus for a few days after the menstrual period stops.

  • Then mucus appears and is cloudy, thick, and inelastic.

  • Shortly before ovulation, more mucus is produced, and the mucus becomes thinner, elastic (stretching between the fingers), clearer, and more watery (like a raw egg white).

Intercourse is avoided completely during menstrual periods (because mucus cannot be checked). It is permitted when mucus is absent but is restricted to every other day because semen may be confused with mucus. Intercourse is avoided from the time mucus first appears after a menstrual period until the mucus completely disappears. After the mucus disappears, intercourse is permitted without restrictions until the next period begins.

If mucus does not generally follow the usual pattern or if a woman has trouble interpreting the mucus, she should consult with her health care professional.

Women who use this method should not use douches or feminine hygiene sprays and creams because these formulations can change the mucus.

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

Symptothermal method

The symptothermal method combines measurement of body temperature at rest (basal body temperature) with the mucus and calendar methods. Thus, of the fertility awareness methods, the symptothermal method is the most reliable.

A woman's basal body temperature increases slightly, by about 0.9° F (0.5° C), after the egg is released. To keep track of changes in temperature, a woman should take her temperature each morning before she gets out of bed. Basal body temperature thermometers are most accurate. If they are unavailable, a mercury thermometer can be used. Electronic thermometers are the least accurate.

The woman notes when cervical mucus increases in amount and becomes thinner, elastic, clearer, and more watery (as for the mucus method) and when temperature increases. She should abstain from intercourse from the first day requiring abstinence according to the calendar method until at least 72 hours after the day her basal body temperature increases and cervical mucus changes.

Lactational amenorrhea method

The lactational amenorrhea method is used after delivery of a baby if a woman is feeding her baby only by breastfeeding (lactation refers to the production of breast milk). Usually, such women have no menstrual periods (called amenorrhea), do not release an egg (ovulate), and thus are not fertile. However, women become fertile 2 weeks before periods restart (when ovulation occurs) and thus do not know they are fertile during those 2 weeks.

This method can be very effective if all of the following are present:

  • The baby is under 6 months old.

  • Breastfeeding is the only source of food for the baby. Supplementing breast milk with formula or solid food or pumping breast milk makes this method less effective.

  • The baby is breastfed at least every 4 hours during the day and every 6 hours at night.

  • Menstrual periods have not restarted after delivery of the baby.

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