Using Basal Body Temperature to Track the Menstrual Cycle
Basal body temperature is one of 3 main ways we can naturally track our cycles, whether that's for preventing pregnancy, trying to conceive or just trying to understand our individual rhythms.
Basal body temperature (BBT) is exactly what it sounds like, our core body temperature at its most rested state. We typically just think of our body temperature as being a sign of whether or not we're sick but it actually is such a good way to monitor other minor shifts in our body.
For instance, your body temperature will go up if you are sick or about to get sick, even just a little. It will also go up if you had a poor night of sleep or consumed alcohol.
In terms of ovulation, our BBT goes up about .7 to 1 deg F after we ovulate. This is triggered by the release of progesterone from the egg as it travels down the fallopian tube. Therefore is a great way to confirm that we've ovulated.
So while things like poor sleep and alcohol may cause temporary increases in our body temp, after we ovulate our temperature will rise and stay risen for the rest of the month until right before our period starts again. Typically a 3 days stretch of elevated body temperature is what I would coach someone to look for to confirm ovulation (in the absence of a cold/flu or other illness).
A common misconception is that BBT can help us predict ovulation. This isn't true except in the case that when tracking over several months it helps us get an idea of when in the month we might ovulate. However, a +/- 3 day variation is completely normal from month to month and your BBT won't rise until after this has happened.
For active women, some statistics report that up to 50% of cycles may be anovulatory (meaning we don't ovulate). This is something really interesting to track in that case because even though you may be having a regular period, you may not be ovulating. If you don't ovulate, you won't see a rise in BBT.
How do you take your temperature:
Many wearables now take body temperature readings and are probably the easiest ways to track this. Things like the Oura Ring, the newest Apple watches and BBT tracking devices like Temp Drop.
You can also use a thermometer under your tongue. Just make sure it calculates to the .01 decimal point. Using this method you should also keep the thermometer by your bedside and take it as soon as you wake up, before you get out of bed.
It’s recommended that you track BBT for about 3 months before drawing any major conclusions so that you have time to establish a baseline of your ‘normal’ and have enough data that you can weed through any device or user error.
Once you have 3 months of data, you can then start to look for trends and use the information as a way to promote conception or prevent pregnancy by timing intercourse either inside or outside of this ovulation window.
Reminder, sperm are capable of living up to 5 days in the vaginal canal so if you are using cycle tracking to prevent pregnancy, be sure to avoid unprotected intercourse 5 days prior to ovulation.
Once you have confirmed ovulation using your BBT (elevated BBT for 3 days) you should be in the clear because conception can only happen in the 24 hour window after ovulation before the egg starts to disenegrate.
I hope this was helpful! Feel free to reach out with any questions or if you’d like more support on your health journey!
