Dear Alice,

In one of your replies, you said "There is a method of natural birth control that combines basal temperature, with observation of cervical mucus, and continuity of an individual woman's patterns" in the context of how a woman can find out about her fertile and infertile periods throughout her cycle. Could you please elaborate on that method?

— Going natural


Dear Going natural,

Getting right down to the bottom of your inquiry, the birth control method that uses basal temperature, cervical mucus, and the calendar method combined is a type of fertility awareness-based method (FABM) referred to as the symptothermal method. There is less than a one percent chance of becoming pregnant while using this specific method if used consistently and correctly, which can be a challenging task for some. The symptothermal method and other FABMs can be used for other reasons besides preventing pregnancy — they can also help women who want to get pregnant identify fertile days and uncover infertility or other gynecological issues.

The symptothermal method combines calendar, temperature, and mucus. Although each of these can be used on its own, Planned Parenthood advises combining the three for improved efficacy. The instructions for each are:

  • Rhythm or calendar method: The rhythm or calendar method estimates fertility based on your menstrual history. Before relying on the calendar method, keep track of your menstrual cycle for at least six months (more is better) while you are not using any hormonal contraception. From your records, find your shortest cycle and subtract 18. For example, if your shortest cycle is 28 days, subtracting 18 leaves 10. Counting from the first day of your period, say January 1, the tenth day of your cycle (January 10) is the first day you're likely to be fertile. To find your last fertile day, look in your records for your longest cycle and subtract 11. So, if you longest cycle is 31 days, subtracting 11 equals 21. That means the 21st day of your current cycle (January 21) is the last day you're likely to be fertile. In this example, January 10 to January 21 are fertile days, when pregnancy due to unprotected sex is more likely to occur. You may want to either avoid sex or use another form of birth control (such as condoms) if you'd like to avoid a pregnancy during that time. The calendar method is not reliable if your cycle is shorter than 27 days or if your cycles are irregular.
  • Temperature method: Most women have a spike in body temperature right after ovulating so it's possible to pinpoint egg release by tracking your basal body temperature. To use this method, take your temperature with a basal thermometer each morning before getting out of bed and record the measurement to the tenth of a degree (e.g. 98.6 degrees) on a graph. Basal thermometers can be used in the mouth or the rectum — so reading the directions before using is key. Most women will see a dip in temperature at the beginning of the menstrual cycle, followed by a spike that lasts several days after ovulation. Day one of your cycle through the third day of higher temperature are considered fertile days when you would want be abstinent or use another birth control method if you'd like to prevent pregnancy. The temperature method may not be reliable if you have a fever, restless sleep, or a schedule that requires you to wake up at very different times each day.
  • Cervical mucus method: Changes in vaginal fluid or discharge can also signal ovulation. There are three types of cervical mucus methods. In the Billings Method, "wet" days (when mucus is present) are considered fertile days and "dry" days (with no discharge) are non-fertile days. Mucus usually appears a few days before ovulation. Sticky at first, the mucus becomes increasingly creamy, wet, and slippery, similar to egg white, signaling peak fertility. To test the consistency, you can take a sample and stretch it between two fingers. To prevent pregnancy, you must abstain from intercourse or use another form of birth control from the time mucus appears until the evening of the fourth day after it disappears. In the Creighton Method, the female examines her cervical mucus and menstruation. The Two-Day Method asks the woman to consider if she had cervical mucus today or yesterday. If the answer to either is yes, pregnancy is more likely to occur if you have unprotected sex during this time. If she answers no to both questions, having unprotected sex during that time is considered less likely to result in a pregnancy.

To discuss fertility awareness as a strategy for birth control, trying to get pregnant, or any other reason, it’s always a good idea to make an appointment with your health care provider. You might also find Planned Parenthood’s FABM and fertility pattern chart to be a helpful online resource. Used consistently and correctly, natural family planning may be a good birth control option for women who desire other contraceptives for personal or health reasons. Just keep in mind that if you "go natural," fertility awareness methods can take a bit of practice and they also don't protect against sexually transmitted infections (STIs) or HIV.


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