Dealing with variables in charting basal body temperatures


One of the most common complaints about natural family planning and charting is because there can be so many variables that come in to play when we begin to chart temperatures using a basal body thermometer.

Variable #1 – wake up times

It’s always best to take your temperature at the same time every day, any variation of more than 15 minutes or so can skew the results of your chart or make it more difficult to read. From my own personal experience in changing my wake times, I’ve noticed that my temps at 6 AM are about half of a degree lower than those taken at 7 AM and other women I’ve talked to have found the same issue.

The way I deal with it is to simply keep my alarm set the same, everyday of the week. But some of us like to sleep in on the weekend *cough* ME *cough*, so waking up at 5:30 AM on Saturdays and Sundays feels like torture, even if I can roll over and go back to sleep after I take my temp.

 Variable #2 – open mouth breathing

Over the last year or so, I’m finding that I’ve been sleeping with my mouth open more often, which has definitely had an effect on my temperatures I take with my oral thermometer. Not a huge variance, but enough to notice.

Some women in our NFW community have had such a hard time temping because sleeping with their mouths open can change their temps by a half of a degree or more, rendering their charts useless, and instead take their temperature vaginally each morning instead. This can definitely take care of variables caused by mouth breathing, but isn’t always something women want to do.

Finding out why you sleep with your mouth open is important though, so check in with both your doctor and your dentist and see if you can’t get to the root of the issue. (Closed mouth breathing is better for not only your sleep, but the formation of your lower face and can impact dental health.)

taking your basal body temperature

Variable #3 – Logging temperatures can be a pain

If you use a simple basal thermometer, you’re also going to have to log your temperature everyday. Some choose to use the pen and paper method, printing off a chart and marking it each morning, others download an app on their phone and enter it that way, letting the software program give them insight on ovulation.

The apps are definitely much easier to use than pen and paper, but I often forgot to log my temp in the morning, especially on days where I went back to sleep after I took it. One way I tried to fix the issue was to get a thermometer that would remember the last temperature taken, and keep my phone on my nightstand (in airplane mode, of course) so that I could enter it right away when I woke up. And if I didn’t remember then, at night time I could turn the thermometer back on and grab that last temp.

Variable #4 – waking randomly throughout the night

Many of us don’t sleep 8-9 hours straight through without waking up at least once and when charting, we want to make sure that we’ve slept at least 3-4 hours straight through before we take our temperature. So, let’s say we go to bed at 10 PM and wake up at 6 AM, but we also wake up at 4 AM for a moment. This break in sleep will disrupt your core temperature as you won’t have enough time to get in 3-4 hours of sleep before the alarm goes off.

I dealt with insomnia for a couple of years after my miscarriage, and trying to chart during that time was much more difficult. Sure, I could take my temp at 4 AM when I woke up, but sitting there for a full minute or two while I took my temp would cause me to fully wake up and then I couldn’t go back to sleep. I finally decided to skip temping until I started sleeping better. It took me awhile, but I finally figured out that my insomnia was caused by a B12 deficiency and low thyroid. So if you’re having trouble with night waking, please do work with your doctor to get to the root of the problem!


Last year I came across YONO Labs when they began a KickStarter campaign for the production of the first in-ear basal body thermometer. You wear it all night long and it takes your temperature throughout the night! (there is NO data transmission while it is in your ear.) The founder asked me then if I wanted to try it out and I jumped at the chance to review it! How could I not?! I’ve been charting on and off for about seven years now – anything I can use to make it easier is definitely welcome. And it takes care of so many of the variables that come into play when charting our basal body temps!

I received my YONO thermometer a few weeks ago and have since used it for a majority of that time, though not long enough for their app to fully understand and predict my cycle. (In this case I’ve still been entering in my temps into another app I’ve been using this last year until the YONO app has enough data for a couple of cycles)

The in-ear thermometer comes with a few different sized ear buds, helping to ensure a good (and comfortable) fit. The entire piece is actually quite soft, and while it sure feels weird at first, it’s not horribly uncomfortable.

YONO wearable basal body thermometer

My first two weeks with YONO:

night one – Opened it right before bed and got so excited I just put it in and hoped it was all working. I also changed ears a couple times that night, trying to figure out which ear was going to work the best for me (it’s recommended to use the same one all night). Woke up in the morning to realize I was supposed to charge it first, doh! I really should read directions first. No data transferred, of course.

night two – Started with it in my right ear and fell asleep as normal. Woke up and took it out around 4 AM because it was bugging me. No data transferred to the app. Huh.

night three – Got an email from YONO reminding me to read the instructions via the app, not just the paper ones that come with it. Realized I was putting it in the ear incorrectly. Placed it in my ear the right way (it was a bit tight – I have small-ish ears) and went to sleep. Finally had some data transferred the next morning! Yay!

night four – Got it charged, wore it all night, data transferred. Success! I feel like I’m finally getting the hang of it.

night five – Forgot to charge it again so I didn’t bother putting it in. I also hopped on Amazon to find a multi-USB charger! The thermometer comes in a small base and they send a USB charging cord…but the cord needs to be plugged in to the outlet base ‘thingy’. And since I have my iPhone plugged in behind my nightstand and the YONO uses the same cord Android phones use… I had to get back there everyday and change the cords. Ain’t nobody got time for that. Now I’m all set and charging is a breeze.

night six – Can’t sleep, had coffee too late in the afternoon and it was keeping me up. The thermometer in my ear was driving me nuts, as was the blankets, the moon light…basically everything. I had to take it out, get up and get a drink, and then went back to bed and try to sleep. I just couldn’t sleep with it in, and it had everything to do with me and not the device.

nights 7-12 – I think I’m finally getting the hang of it! I don’t notice it much while I sleep and it doesn’t bother me anymore. It’s just there and how I sleep now. Data transmission every night without problem.

nights 13 and 14 – Had kids wake me up a couple of times during the night, but with YONO I still got my temp readings and it was interesting to look at the data from those nights and see the rise in my temps from when I woke up!

Benefits of the YONO in-ear thermometer

  • Measures core body temperature instead of skin temperature, which can easily be affected by ambient temperature. I also don’t have to worry about my oral temp being thrown off by my mouth breathing.
  • It easily connects to the YONO App which uses the readings to plot a monthly BBT chart, analyzes the data, and predicts the monthly fertile window. It’s as easy as replacing the ear bud into the charging station, closing the lid, and hitting the “connect” button on the app. It takes just seconds and you have your entire nights temperature readings!
  • YONO also offers the more insightful, overnight, and continuous body temperature data, as compared to a traditional basal body thermometer, which collects only one data point. It’s really been interesting to see what my temperatures do all night long.
  • You can also connect to Apple’s Healthkit and they are also going to be working with other health and wellness applications to provide customers a convenient way of collecting data.

Overall, I’ve had a positive experience using the in-ear basal thermometer, but there are a few things I also want to mention.

  • I do think there is definitely a short learning curve as you get used to the feel of it while sleeping. Now that I’ve gotten used to it, I barely know it’s there unless on sleep on the ear that it’s in for too long. The first few nights it felt weird for sure!
  • There were a couple of times were a child cried/came in my room and I didn’t hear them. (granted – this may have been a good thing since my kids are all older and should be sleeping. lol) But I tend to side sleep, so if one ear is on the pillow and the other has the ear-bud in…I don’t hear much around me! I could see how it may be problematic if there was a young infant in the house and no significant other to help out with nighttime waking.
  • It’s small…and I have a dog. I can easily see how this device could be lost or eaten by a (stupid) dog! Especially if you take it out during the night and don’t place it in it’s charging station right away like you would in the morning. It’s reasonably priced…but not for constant replacing!
  • If you travel often and have an Android phone, it will be easier when they come out with the Android app! Right now the app is only available on iPhone, but it uses the same charging port that Android does, so that means two chargers have to come along. It will be easier for me to charge the YONO during the day and then plug my phone into the same charging cord at night. (Right now I’m using my old iPhone for the app)

The YONO in-ear basal body thermometer is currently available for pre-order and retails for $149.00. I’m really excited about this technology and can’t wait to see how the company grows and continues to make it better and better.

Donielle Baker

Donielle Baker

owner and editor of Natural Fertility and Wellness at Natural Fertility and Wellness
I believe women can learn how to heal their bodies & balance their hormones through natural methods. An advocate for natural health, I have a passion for nourishing/real food nutrition and natural living. My personal background includes both infertility and miscarriage and I started Natural Fertility and Wellness in 2008 in order to share all of the information I found helpful in my journey to heal from PCOS and overcome infertility.
Donielle Baker
Donielle Baker
Donielle Baker
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