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Feel like you’re doing ALL OF THE THINGS when it comes to tracking your menstrual cycle and ovulation?
BUT for some reason, there seems to just be that something missing that means things haven’t *quite* clicked into place yet.
When it comes to tracking Basal Body Temperature (BBT), so many women seem to get bogged down in the specifics of daily temperatures and over-analysing the numbers instead of looking at the bigger picture – the overall temperature pattern throughout a cycle.
You probably know by now that I firmly believe you can get all the information you need by observing your cervical mucus patterns, but tracking your BBT comes in a very close second place because it can give you some really valuable insights into your cycle.
In this episode of the podcast, I’m sharing the 3 temperature shifts you should be tracking every cycle and what they can tell you about ovulation, your next period and it may even reveal to you one of the earliest signs of pregnancy.
Let’s begin by talking about what your BBT actually is and why we track it throughout our menstrual cycle.
Charting your basal body temperature (BBT) can be combined with charting your mucus if you want an extra indicator of ovulation and where you are in your menstrual cycle. If you can clearly identify fertile mucus and you’re really confident in tracking the changes throughout your cycle, then you might not need to track your temperature. But, if you want a back-up, if you want a second source of information, or if you’re not seeing clear differences in your mucus throughout your cycle then you may find tracking your temperature helpful.
Basal body temperature (BBT) is the body’s resting temperature after at least 4-6 hours of uninterrupted sleep. It is assessed by taking your body temperature orally first thing in the morning after waking up and before any physical activity. The most accurate readings are given before we start moving around for the day, so try to take your temperature as soon as you wake up while still lying in bed. So not only is this before you get out of bed to pee, before you get up and put the kettle on, this is before you really move at all. It’s before you roll over to snuggle with your partner, before you start playing on your phone. As soon as you wake up and go into that half-awake, half-dreaming state where you know you’re awake but not yet ready to open your eyes, you take your thermometer that you put on your bedside table the night before, and you pop it in your mouth for a couple of minutes. When it beeps, take it out of your mouth, check your temperature and add it to your chart for the day. What I like to do is just take it straight out and pop it back on my bedside table without even looking at it. When I’m actually getting out of bed, I’m awake and slightly more conscious, then I turn the thermometer back on and look at the last recorded temperature. Then I’m in a better state to actually remember the numbers on the screen and write them down.
You will need to use basal body temperature thermometer, or an ovulation thermometer, which is an oral thermometer that is accurate to 2 decimal places (Celsius) or 1 decimal place (Fahrenheit). Since having a baby and when tracking my temperature now, I no longer use an oral thermometer. These are of course very handy and affordable, you can just get one from the chemist. The problem with an oral thermometer is that you need that 4-6 hours of uninterrupted sleep which is not happening for me right now. So I invested in a Tempdrop tracker which I wear on my arm all night and it syncs up with an app in the morning and tells me my body temperature overnight. This has been incredibly useful in tracking the return of my fertility, especially when my mucus patterns aren’t as clear-cut as they were pre-pregnancy. The Tempdrop is great because it eliminates a lot of those margins for error compared to an oral thermometer, but if you’re just getting started with tracking then an oral thermometer is absolutely fine.
The best advice I can give you is not to try to over-analyse your temperature reading every single day. Sometimes our temperature for the day can be off. Maybe we didn’t sleep well, maybe we’re hot and bothered, maybe we slept in for an extra hour or two. It’s very common and completely normal to see one or two really wonky temperatures that are either unexpectedly high or low and make no sense in the context of a complete chart. This is normal but it’s the reason why you cannot rely just on temperature to tell you if you’re fertile, compared to mucus which can tell you what’s going on that day. What we want to look at with our temperature is the overall pattern throughout our cycle, because the day after ovulation, our temperature rises. And it stays high until our next period.
There are 3 key temperature shifts that can occur within a cycle and these shifts can give you incredible insight into where you are in your cycle, whether you have ovulated and it may even be one of your earliest signs of pregnancy!
The reason that these temperature shifts occur is due to the hormone progesterone. This is the hormone that surges in the second half of your cycle after ovulation has occurred and it’s the hormone that wants pregnancy to happen. It’s the key hormone in establishing and maintaining pregnancy and when an egg is released from a follicle inside the ovary at ovulation, the follicle that remains becomes the corpus luteum. The corpus luteum secretes progesterone. This occurs during the luteal phase of the cycle, after ovulation. If the fertilised egg implants in the endometrium and pregnancy has occurred, progesterone levels will remain high to maintain the pregnancy. If the egg was not fertilised, progesterone levels will drop, quite suddenly, causing the endometrial lining to shed and your next period occurs.
Understanding how progesterone levels fluctuate throughout a typical menstrual cycle will help you to understand and predict what your BBT will do also. Because if you looked at this visually, you would see that the rise and fall of progesterone levels and BBT are very similar.
BBT is used to retrospectively confirm ovulation. This means that your cervical mucus will give you a more accurate, real-time indication of when ovulation is approaching through wet, fertile-quality mucus that we see in the fertile window, but BBT can help to confirm it has happened. It does so by a rise in BBT of 0.2 – 0.5 degrees (Celsius or Fahrenheit) that remains high until your next period. Ovulation usually occurs the day before we see the temperature shift; the last day of low temperatures, but can be delayed in some women. If your peak day, the last day of fertile mucus, does not line up with your temperature rise, which may happen 1-2 days later, you should always go by your cervical mucus as the key fertile sign and use the last day of fertile mucus as ovulation day, and then use that upward shift in BBT to confirm that your mucus observations were correct. If your fertile mucus stops, and you shift to a dry sensation or sticky mucus, and you don’t observe this upward temperature shift, then there is a chance ovulation has not occurred and your body may need to attempt ovulation again, meaning fertile mucus will return. It’s BBT that can help you to confirm this.
With experience, you’ll learn when it happens for you based on your mucus peak day. We would then expect BBT to remain high until your next period. We can confirm that we have definitely had a temperature rise when 3 consecutive temperatures are higher than the previous 6. So, BBT taken for the first 3 days after ovulation will be higher than the 6 days previously.
The day your BBT drops again, you’ll likely get your period that same day and it’s the best way to wake up knowing that it’s arriving so you don’t get caught out. If you are trying to conceive, please don’t be too disheartened by a low temperature because remember we can get some wonky temperatures in there, including a lower temperature post-ovulation. It is handy to know this information however, because it means you won’t get caught out if your period does arrive.
This temperature drop occurs due to the drop in progesterone when the body realises it isn’t pregnant, and so starts preparing to shed the thickened endometrial lining as your next period. It’s the pregnancy hormone after all, so levels will drop if pregnancy hasn’t happened.
Once again, if you are trying to conceive, don’t be too disheartened if you don’t see this one, as this isn’t necessarily detectable in all pregnancies. Implantation is the final step of conception. First, we have ovulation, then fertilisation, then finally implantation. During each menstrual cycle a follicle within one of the ovaries ruptures and releases an egg – ovulation. The egg travels into the fallopian tube, where it must be fertilised by a viable sperm in the next 24-48 hours. The egg is then transported down into the uterus and, if fertilised, implants into the endometrium. From here the egg will develop into a foetus.
Implantation usually occurs about 12-14 days after ovulation and can be as early as about 7 days and takes about 24-48 hours. This is why we need our luteal phase to be at least 10 days long, and why it’s usually anywhere from 10-17 days long. We need to give our body enough time for implantation to occur. And this is why it’s so important to look at things like our progesterone levels when trying to conceive, to really make sure our luteal phase is long enough for implantation to occur.
The temperature spike we see at ovulation is due to the sudden surge in progesterone levels produced by the corpus luteum that forms from what remains of the ovarian follicle after ovulation. This jump is anywhere from 0.2-0.5 degrees and it’s our way of confirming ovulation. You may see a second surge in temperature, not as obvious as the ovulation surge, which can happen around implantation, due once again to another surge in progesterone. So on your chart, you might notice a second jump in temperature about a week after ovulation, which could be a sign that implantation has occurred. Not seeing this does not mean you are not pregnant. Stick with the charting principles that you hopefully are familiar with by now, if you know the length of your luteal phase and you’re not seeing a drop in BBT around the time you expect your next period, then you can consider taking a pregnancy test.
Some women may notice an implantation dip or ovulation dip, in the day before ovulation happens, where you will see a lower than average temperature the day before the upward surge. I don’t often talk about this dip because I don’t think it’s a significant thing to look out for, it can just add to the confusion, because the spike in temperature is actually more important than the dip. Not all women experience a dip before ovulation, just as they may not see a dip at implantation, but it’s typically one day of lower temperature followed by a surge.
Sometimes we can get some wonky temperatures. A number of factors can influence your basal body temperature, and some women find that they are particularly sensitive to even minor disruptions. These might be:
You could take your temperature orally 3 times in the morning, and it’s highly likely you will get 3 different temperatures. This is why you don’t need to fixate on the numbers themselves, but the pattern compared to the days before. It’s these kinds of situations where trackers like the Tempdrop can be really handy in eliminating some of these factors, if you’re finding that you’re not making sense of your readings from an oral thermometer.
3 simple steps to find out exactly when you're ovulating (without tracking apps)
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