Before tracking our cycles, the only time we would have to pull out a thermometer is when we or someone in our life had a fever! Many women track their cycles using what’s called basal body temperature (or BBT, for short). Tracking our BBT tells us where we are in our cycles because it is our lowest body temperature attained during rest and changes according to our cycle.
A pattern in our BBT will reveal when we’ve ovulated in our cycle. This is because progesterone, the hormone that is most dominant in the luteal phase after ovulation, raises our resting body temperature by a very slight amount. While the only way to 100% nail down when ovulation happened is through an ultrasound, BBT can get us pretty close to the time that ovulation has happened.
BBT is a retrospective marker of ovulation. This means that a change in BBT will only happen after ovulation has taken place. There are apps and devices marketed to determine your fertile window (the time when conception can occur) based on temperature alone. Don’t be fooled by these claims!
While ovulation can be confirmed after it happens with BBT, there is no way an app can tell us ovulation is about to occur or when it is just around the corner. Calculations such as those in the Symptothermal double-check methods can let us know at the beginning of the cycle an approximate time the fertile window will open, as will tracking our cervical mucus. As we approach ovulation, our cervical mucus responds to the influence of estrogen and will change as we get closer to ovulation based on the levels of estrogen.
Tracking BBT for Conception:
You may have heard of folks tracking their cycles in order to time intercourse if they are wanting to conceive. As women we are only able to get pregnant about 5-7 days per month! This is not a long period of time! Consider someone who has been trying to get pregnant and hasn’t tracked their cycles - they may be completely in the dark as to when they can reasonably conceive in the cycle.
Tracking your BBT when trying to get pregnant can let you know if you are ovulating (which you need to do in order to make a baby!), and when that takes place in your unique cycle. Contrary to popular belief, not everyone ovulates on day 14 and gets their period on day 28! Your cycle is unique to YOU, and tracking ovulation with BBT means that you increase your changes of timing intercourse to get pregnant.
Tracking BBT for Avoiding Pregnancy:
While you can track your BBT to get pregnant, the wonderful thing about this practice is that you can also track your BBT to avoid pregnancy. This is also known as the symptothermal method of fertility awareness. Symptothermal methods of fertility awareness track both BBT and cervical mucus, and occasionally other fertility signs like cervical position.
Remember when I mentioned those apps and devices that claim to identify the fertile window for you? Those are not the same as fertility awareness for avoiding pregnancy. Using BBT to avoid pregnancy is one piece, but you also need to track cervical mucus and learn the rules yourself or work with an instructor.
Fertility awareness based methods (FABMs) work by helping you identify the fertile window, or that time in your cycle when conception is possible, and then let you decide what you would like to do during that time, depending on your intentions!
In order to track your BBT to find ovulation you will need:
- To track your cycle on paper or in an app that has BBT tracking. Some of my fave apps are Kindara, Ovuview or Fertility Friend.
- A basal body thermometer, such as Tempdrop. A basal body thermometer is not the same as a fever thermometer! It is more sensitive and goes up to 2 decimal places.
- Track your BBT daily and, if using an oral thermometer, take it at the same time every day before getting out of bed, after at least three hours of sleep (with Tempdrop, a wearable thermometer, you’re able to skip this step and you won’t need to wake up to take your temperature).
- Watch for a sustained shift of at least 0.2C/0.4F above the previous six temperatures that stays high for at least three days. There are more nuances to this, which I encourage you to seek help from an instructor or other resource if you are finding this part confusing! Tempdrop recently published an Intro to Fertility Awareness that I highly recommend downloading for a more nuanced guide to ovulation tracking.
Nathalie Daudet is a social worker and FEMM instructor based in Winnipeg, Canada. She discovered fertility awareness after searching high and low for a non-hormonal method of birth control. After learning the magic of fertility awareness and the gift of body literacy, she decided to pursue formal fertility awareness training and share the knowledge of fertility awareness with women looking for a natural birth control option. Fertility Awareness Project is the hub for Nathalie’s FEMM classes in both group and individual formats, online and in person in Winnipeg. If you love this post and would like to thank Nathalie, shop Tempdrop with Nathalie's unique referral link.