Charting 101 - Lesson #2: Basal body temperature
In this lesson on the Fertility Awareness Method we discuss the key way to know if you've ovulated: basal body temperature. As always, to learn more please read the book Taking Charge of Your Fertility.
If you would rather view this blog in video format, click here:
What exactly is basal body temperature, and why does it matter? This is Charting 101, lesson #2.
Basal body temperature, aka waking temperature or BBT, is your lowest resting temperature. It’s taken first thing in the morning, before you get out of bed, talk, or check your phone. Once you start moving your temperature will increase, so we want to check your temperature before that.
When you chart your waking temperature daily, you’re not looking for a single number. You’re looking for a pattern over time.
Before ovulation, temperatures are lower. After ovulation, progesterone is released by the corpus luteum to prepare the uterus for potential implantation of a fertilized egg, and a side effect of progesterone is increasing your body temperature (think "bun in the oven"!). That increased temperature will be maintained until your menstruation begins the next cycle. The temperature shift is how we confirm that ovulation has occured.
This is why BBT is a confirming sign, not a predicting one. It helps tell you when your fertile window has closed, not when it’s about to open. This is why we don’t recommend apps that only rely on BBT.
For accurate charting, consistency matters. Try to take your temperature at the same time every morning, after at least 3 hours of sleep, using a basal thermometer (you can find them for ~$10 on Amazon). There are also wearable thermometers if you don’t like waking up at the same time every day (we like Tempdrop!).
Follow along for more Charting 101. Next, we’ll talk about cervical fluid and how it helps identify the start of your fertile window. And if you’re ready to start charting, download Cyclisity.
As a legal disclaimer, I want to add that this blog post is about the Fertility Awareness Method, not Cyclisity. Cyclisity is an app that helps women chart their cycles but is for informational and educational purposes only. It is not FDA approved as a medical device and does not provide any medical advice. Please consult your physician with any health questions you may have.