Trying to conceive (TTC) centers around one key event in a woman’s menstrual cycle each month: ovulation! Ovulation occurs when an egg releases from an ovary. The egg then moves into the fallopian tube and is available for fertilization. Since experts believe sperm can live inside the female reproductive tract for up to five days, timing intercourse in the few days before ovulation is thought to give you the best chance of conceiving in a given month. The goal is for sperm to be ready and waiting when the egg is released. But how on earth do you know when that will be?
In this post, we’re going to explore the basal body temperature (BBT) method, which is an ovulation tracking method that can help give you a better idea of when you might be ovulating each month! If you are new to ovulation tracking, I would recommend also reading my blog post on the calendar method and cervical mucus method. Beginning with those basics will give you a great starting point before diving into the slightly more involved BBT method.
Why is Tracking Ovulation Important?
If you are TTC, identifying your fertile window (the few days each month you are most fertile) is key because it can be very easy to miss it. According to experts, the fertile window is comprised of the five days prior to ovulation and the day of ovulation itself. With such a small window to aim for each month, it is very helpful to gather as much information as possible that could provide hints of when you may be ovulating. You can then adjust the timing of intercourse to align with your fertile window. Doing so will help optimize your chances of becoming pregnant!
Things to Keep in Mind
Before we get started, I want to point out that I am not a doctor. My advice is based on extensive research. It’s also important to note that these ovulation tracking methods are clues to help you estimate when ovulation might occur but are not a surefire way to pinpoint the exact timing of ovulation.
According to experts, the exact timing of ovulation can only be confirmed via ultrasound. But, yikes… that would get expensive! The BBT method is a lower-cost option and can be done from the comfort of your own home (your bed, actually) while still helping you gain some helpful insight into the possible timing of ovulation. With this in mind, let’s explore the BBT method and track that egg!
Basal Body Temperature (BBT)
The BBT method can do wonders for helping you better understand your body, fertile window, and potential ovulation timing. The main thing to keep in mind with the BBT method is that, just like cycle tracking and the calendar method, it is retrospective. What I mean by this is it is a tool that gives you clues on the timing of ovulation after ovulation has already passed. So, it should not be used as a predictor of ovulation. I’ll touch more on this in a bit.
Your basal body temperature is defined as your temperature at complete rest (typically, first thing in the morning). Experts believe that your BBT will increase very slightly (roughly 0.4 – 1.0 degrees F) 1-3 days after ovulation due to increased levels of the progesterone hormone. The idea is that if you can identify this temperature shift, you will be able to estimate when ovulation may have occurred for you in the current month.
Taking Your BBT
Since the temperature shift you’re trying to identify is extremely slight, it is important to use a basal body thermometer to take your temperature. These types of thermometers are designed to be more sensitive and precise as they typically give temperature readings to the hundredth degree (rather than to the tenth degree like regular thermometers). Regular thermometers simply aren’t as sensitive and typically won’t give you as accurate of a reading. Not sure how to find a basal body thermometer or which one to pick? Keep reading because I share my favorite basal body thermometer below!
In addition to using a basal body thermometer, there are several things you will need to do in order to make sure you are getting as accurate of a reading as possible. Experts recommend that each morning, you should take your BBT:
- At the same time
- Using the same thermometer
- Using the same method (orally, vaginally, etc.)
- Before getting out of bed, sitting up, talking, drinking water, etc.
- After getting at least four hours of continuous sleep
Again, since it’s such a slight shift in temperature, your readings could be less accurate for reasons such as being ill, having large fluctuations in the amount of sleep you’re getting each night, and even drinking alcohol the night before. If you get an “outlier” reading on a given day for a reason such as these, and your temperature goes back to your normal range the following day, it is typically advised to simply disregard that one reading.
However, it is definitely possible to still have a noticeable temperature shift each month even with slight fluctuations such as these. Try to stay consistent with your lifestyle and sleep patterns while using the BBT method, but don’t stress too much if you have fluctuations here and there.
Using your cycle tracking app (or other preferred method of tracking), you should record your BBT each day of the month in a line graph format. (Cycle tracking apps will chart the temperatures on a line graph for you if you just enter your daily temperatures.) The temperatures themselves are not as important as the presence of a temperature shift, which is thought to occur just after ovulation.
During your follicular phase (the time between the first day of your period and ovulation), your BBT is relatively on the lower end. Then, 1-3 days after ovulation, your temperature elevates and stays elevated throughout the rest of your cycle. This creates two visibly-noticeable temperature phases (a lower pre-ovulatory phase and a higher post-ovulatory phase), also known as a biphasic pattern.
Reading Your BBT Results
One of the first questions you might have when using this method is what constitutes a true temperature shift and how to identify it. The general rule is that a temperature shift can be confirmed once your BBT has risen at least 0.2 degrees F above your highest BBT from the previous six days AND stays elevated by that margin for at least 3 days. Once you have identified the temperature shift, experts advise treating the last day before the temperature shift as the day of ovulation.
See below for an example of what a BBT chart could look like and how to interpret it. In this instance, there was a noticeable temperature shift on cycle day 14. This means ovulation can be estimated for cycle day 13 (or technically even as far back as cycle day 11 since experts say it can take up to three days after ovulation for the temperature to shift). This looks like a huge temperature shift in graph form, but it was actually only an increase of 0.8 degrees F! This is why it’s so important to use a more sensitive and precise basal body thermometer that will pick up on these slight temperature shifts.
Combining Ovulation Tracking Methods
If taking your temperature at the same time each morning sounds irritating to you, you don’t have to do so for the full month if you don’t want to! If you use the calendar method and cervical mucus method (click here for my separate blog post on these), you will likely already have a general idea of when you might be ovulating. Once you identify the few days when you think you are expecting ovulation, you can start taking your temperature a few days before that. You can then stop taking your temperature once your temperature shift has been sustained for 3 days (since that is when it is considered safe to assume ovulation has occurred).
The BBT method is even more powerful when combined with Ovulation Predictor Kits (OPK’s) because the two methods together create an “ovulation sandwich.” (I will be writing a post soon specifically on OPK’s, so stay tuned!) Since the OPK method gives you about 1-2 days’ notice prior to ovulation, and ovulation occurs about 1-3 days before the temperature shift, the estimated ovulation date is thought to be sandwiched between the two.
For example, in the visual shown above, the temperature shift occurred on cycle day 14, which led us to believe ovulation occurred sometime between cycle day 11 and 13. If the OPK method was also being used and the test turned positive on cycle day 12, you could then reasonably estimate that ovulation occurred right in the middle on cycle day 13. So cool! That is why using both the OPK and BBT methods allows you to estimate ovulation with more precision. The more tools you incorporate, the more insights you will gain.
A Retrospective Tool
It is very important to remember that the BBT method should NOT be used as a predictive tool for identifying the timing of ovulation in the current month. Since your temperature does not shift until after ovulation, it is usually too late to have intercourse after it is identified. (Well, you can definitely still have intercourse! It is just less likely to result in a baby.) However, the BBT method is an excellent tool for the following:
- Indicating the probable occurrence of ovulation (If you are consistently not seeing a temperature shift each month while using the BBT method correctly, it is worth mentioning it to your healthcare provider.)
- Identifying when the current month’s fertile window has likely ended
- Estimating the timing of ovulation for future months
- Identifying your typical luteal phase length, which is the time between ovulation and the beginning of your next period (Experts recommend speaking to your healthcare provider if your luteal phase length is less than 10 days.)
Basal Body Thermometers and Resources
I highly recommend the iProven Basal Body Thermometer for the following reasons:
- It shows your temperature at the hundredth degree. (High sensitivity makes all the difference when trying to identify your temperature shift.)
- It saves your most recent temperature reading for later reference. (This allows you to just go back to sleep after taking your temperature and refer back to it later once you’re more awake and ready to record it in your cycle tracking app.)
- It has a soft, quiet beep. (If you sleep next to someone, they will appreciate this feature considering you will be taking your temperature in the early morning hours each day.)
Fertility Friend is also a very popular resource for all things BBT. They provide many resources, tools, and examples for BBT charting. It is also a great platform to get plugged into if you’re interested in interacting with a community of fellow women who are TTC.
When you are TTC, you naturally want to do everything you can to optimize your chances of becoming pregnant. One of the most helpful things you can do is align intercourse with your fertile window. If you have intercourse during the days leading up to ovulation and/or on the day of ovulation itself, you increase your chances of sperm being able to meet up with the egg and fertilize it.
Being able to optimize the timing of intercourse directly depends on estimating the potential timing of ovulation with as much accuracy as possible. By incorporating the BBT method, you can begin to gain some great insights into when your egg might be released each month.
I would love to hear about your experiences with ovulation tracking! If you have any questions or additional insights pertaining to the BBT method, please share them via the comment box below.
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