Fertility awareness: The symptothermal method

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 basal temperature method, the cervical mucus method, and the calendar method are all forms of fertility awareness-based methods (sometimes called natural family planning) that can be used to reduce the risk of pregnancy. Using fertility awareness-based methods generally have a 76 to 88 percent effectiveness rate. Although each of these can be used on its own, many health experts advise combining the three for improved efficacy. The combination of the three is sometimes referred to as the symptothermal method. This method and other FABMs can be used for reasons other than preventing pregnancy — they can also help people with a uterus who want to get pregnant identify fertile days and uncover infertility or other gynecological issues. Keep reading for more detail on these three methods!

The calendar method estimates fertility based on menstrual history. Before relying on the calendar method, it’s best to keep track of the menstrual cycle for at least six months while not using any hormonal contraception. To determine how long a menstrual cycle is, note the first day of a menstrual cycle and the first day of the next. The length of a cycle is the number of days between each period. 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, count 10 days — this is marked on the calendar as the first potential fertile day. In order to find the last fertile day, the number 11 is subtracted from the longest cycle. For example, if the longest cycle is 31 days, this leaves 20, making the last fertile day 20 days after the beginning of the cycle. It may help to use dates as an example to better understand how this method works. Using these cycle lengths, if the beginning of the cycle begins on January 1, the first fertile day begins on January 10 and the last fertile day is January 20. These dates are 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 isn’t reliable if your cycle is shorter than 27 days or if your cycles are irregular. Some people use the Standard Days method, which is a more simplified version of the calendar method. This method relies on having regular periods and cycles that are never longer than 32 days or shorter than 26 days. In these instances, they wouldn’t have vaginal sex during days 8 through 19 of their cycle.

The next method is the temperature method. Most people with a uterus have a spike in body temperature right after ovulating, so it may be possible to pinpoint egg release by tracking the basal body temperature. To use this method, take the body’s 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. It’s key that the basal temperature be taken before doing anything in the morning, even small activities such as talking, eating, or going to the bathroom in order to get the true basal temperature. Basal thermometers can be used in the mouth or the rectum — so reading the directions before using is key. Most people with a uterus will see a dip in temperature at the beginning of the menstrual cycle, followed by a spike that lasts several days after ovulation. Before using this as a contraceptive method, it’ll be helpful to have three cycles worth of charting to be sure you understand what you’re reading and to establish patterns. Since temperature increases after ovulation, the days in which it’s considered lower risk to have sex without other forms of contraception begins at least three days after the increase in basal body temperature. The period of low risk days ends when the temperature begins to decrease before the next menstrual cycle begins. 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. It can also be helpful to note these changes on your chart to help differentiate what is or isn’t part of the menstrual cycle.

Another method is the cervical mucus method. Changes in vaginal fluid or discharge can also signal ovulation. This method relies on looking at and touching the cervical mucus every day. Mucus isn’t tracked during menstruation as the blood covers mucus that leaves the body. Once the period ends, the cervical mucus can be checked in multiple ways. It can be checked by looking at it and feeling it on toilet paper before urinating, looking at the discharge in the underwear, or putting clean fingers into the vagina to examine the mucus. The most effective way to note the texture of the cervical mucus is to rub it and pull it between the fingers. When using this method, days where the risk of pregnancy is reduced are those when the mucus is cloudy and sticky, as slippery mucus can be an indication that the body is nearing ovulation. The days during menstruation are also considered at a higher risk for conception. Before using this method to prevent pregnancy, it can be key to avoid vaginal sex for a cycle, as sex can cause the body to produce more mucus and it may be confusing while learning mucus patterns. A simpler way of using the cervical mucus method is called the Two-Day Method. The Two-Day Method considers if there was cervical mucus today or yesterday. If the answer to either is yes, pregnancy is more likely to occur if having unprotected sex during this time. If the answer was no to both questions, having unprotected sex during that time is considered less likely to result in a pregnancy.

To keep track of these methods, people use a number of different tools. For the calendar method, this information can be tracked with a standard calendar or a period tracking app. For those using the Standard Days method, some may use an app or a string of beads that let them know where they are in their cycle. The temperature method can be tracked on a fertility awareness chart, while the cervical mucus method can be tracked on a similar chart. Both of these charts can be obtained from a health care provider. The United States Food and Drug Administration (FDA) has recently allowed the marketing of a mobile application called Natural Cycles that will track the basal temperature for users. Note that while it has been FDA approved, it only tracks one of these three forms of FABMs. However, no matter how the information is tracked, the key to maintaining effectiveness is tracking this information consistently and correctly each day.  

To discuss fertility awareness as a strategy for birth control, trying to get pregnant, or any other reason, it’s a good idea to make an appointment with your health care provider. Just keep in mind that if you "go natural," fertility awareness methods can take some practice and dedication. It can also be helpful to note that they don’t protect against sexually transmitted infections. That being said, when used consistently and correctly, fertility awareness-based methods may be a good birth control option for those who desire contraceptives that are non-hormonal or don't require devices for personal or health reasons.

Last updated Aug 24, 2018
Originally published Dec 10, 1995

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