How to BBT
eg. A triphasic BBT Chart
(showing no conception for this cycle)
Why is tracking your Basal Body Temperature (BBT) a good idea?
Charting your basal body temperature (BBT) is an incredibly useful tool that maps out your cycle each month. Taking your temperature daily and plotting the readings on a chart will give you a visual narrative of each phase of your cycle; the follicular, ovulation and the luteal. Many women find tracking their cycle to be an invaluable resource, helping them to understand the micro machinations of their body, eg; showing their ovulation or fertile window, enabling them to plan ahead if trying to conceive (TTC) naturally, or share the information with a therapist or an Assisted Reproductive Therapies (ART) clinic.
If you’re trying to conceive naturally, understanding the fluctuations in your BBT and learning to read your chart will give you a better idea of when your ovulation / fertile window occurs. Conversely, it’s also invaluable if you’re experiencing issues with your cycle, and/or ovulation and therefore you may be considering some form of ARTs. A chart shows clearly if there are phasal disturbances ie; too short, too long, temperature too high or too low, suggesting hormonal disruption or indeed if you haven’t ovulated. All of these anomalies will obviously need to be investigated further, if they show up.
It’s important to note that Ovulation Test (OT) sticks are useful, they work by detecting Luteinising Hormone (LH) which can remain present in urine for up to 12 hrs after release. LH triggers the rupture of the follicle and release of the egg ie ovulation. However, problems with this method may occur. If you have been retrieving negative results, even though you’re sure you have ovulated, it may be that you’re testing consistently outside of your 12hr ovulation window. For example, if you test each morning at 7am and you ovulate a few hours later ie 10am, by the time you test the following morning, there may be little to no LH remaining in the urine to indicate that an ovulation has taken place. Some women have experienced frustration with the OT method as they may be ovulating at a time that is outside of the testing window. However, BBT charting can be used in combination with OT or alone as an alternative method.
What is Basal Body Temperature (BBT) ?
BBT is the baseline body temperature taken immediately after waking from a night’s sleep with a dedicated BBT thermometer.
At the time of ovulation there should be a small but significant rise in temperature, due to the release of the hormone progesterone, Once the lead follicle is ripe usually at D12-14 of a normal cycle, ovulation occurs with the release of the egg from the ovary, leaving behind the corpus luteum or rupture site, which in turn, triggers the release of progesterone. The increase in temperature provides an hospitable environment for the egg as it travels through the fallopian tube on its way to the uterus. Recording your temperature daily will clearly show if ovulation has taken place.
What factors adversely affect BBT?
Sleep: Many women worry that waking later will affect their temperature readings and skew the chart. This is indeed true but it’s also important to prioritise sleep. So a simple calculation can be made to adjust your temperature for those days. The same is true if you are not getting enough sleep, as this can have an impact on your resting body temperature. Making notes of these events on the chart is useful.
Alcohol: Consuming any alcohol can elevate body temperature, there is no calculation to make re-adjustments.
Sickness: Of course if you have a fever, this will effect the body’s resting temperature.
Chronic illnesses or conditions: Such as hypothyroidism, and those going through peri-menopause may also experience fluctuations in basal body temperature.
Some medications: It’s always best to have a discussion with your GP/ Gynae to check if your medications could affect your BBT.
How to BBT Successfully
The picture above (top of page) shows a Typical BBT chart with a standard cycle length of 28 days,
a standard Follicular phase, from Day 1 (taken from the 1st day of your period *)
to Day 11 or 12 with Ovulation occurring on D14/15 in this chart shown by the slight increase in basal temperature followed by the progesterone spike. The ovulation section often looks like 2 peaks that form an abstract W, over a 5 day period which indicates the ‘fertile window’
The 2nd phase after ovulation is the Luteal phase and should reach at least +0 .4ºc over the follicular phase, to show adequate progesterone levels are present to allow for conception
if conception doesn’t take place, your temperature will begin to decline as progesterone levels fall off, and the body will prepare for menstruation.
This tool provides a record of cycle length and regularity, as well as highlighting any disturbances with ovulation, or possible hormonal imbalance.
The key to taking a BBT chart successfully is to follow the instructions on how to take your temperature, and to not get stressed if you miss taking it or if you take it too late or early - see guidelines below under the How to BBT section.
Method
The Basal Body temperature is your resting temperature and must be measured first thing in the morning, as soon as you wake, before you sit up, talk, or get out of bed. Recording your basal temperatures indicates key stages of your cycle and can help you pinpoint the optimum time to conceive ie your fertile window
How to Measure your BBT - I recommend using a dedicated BBT thermometer that shows two decimal places in large type. Temperature readings must take place first thing in the morning, to record the body’s lowest resting temperature before doing anything else even talking. Temperature readings may also be taken using a wearable device like an Oura Ring or Apple Watch. However, wearable devices work slightly differently from a BBT thermometer, as they measure continually throughout the night.
Be Consistent - To ensure accurate readings measure your temperature with the same thermometer at the same time each day. Get at least three hours of uninterrupted sleep each night for the best results. If you have a bad night’s sleep you should skip measuring until the next day. If you wake up at a much earlier or later time than usual, adjust your reading by using a BBT temperature adjuster formula on google search.
Track your temperature mid-cycle. It’s helpful if you have a regular period cycle, knowing how many days long your cycle length is can help you estimate when you should be ovulating. If you have a 28 day cycle ovulation is commonly around D14 counting D1 as the first day of your period if it started between 12am and 12pm that day. If it started after midday that day the following day should be counted as D1. It is probably a good idea to start testing on Day10 - D12 of your cycle and continue testing for 5 consecutive days.
The Fertile Window - A small rise in temperature for at least 5 consecutive days is a clear indicator that ovulation has happened. If your BBT is between 97.6°F (36.4°C) and 98.6°F (37°C), you have most likely ovulated and will be fertile during this time. The oocyte or egg cell can live for 24 hours and sperm can live for up to five days. BBT will drop again if pregnancy doesn’t happen, this will herald your period and signal the start of a new cycle.
