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Explaining the Unexplained: BBT charting

Explaining the Unexplained: BBT charting

Here Alex O'Connor, a fertility acupuncture specialist, from Essex Fertility in her Explaining the Unexplained series gives us all the details on BBT charting and how to really get to know your cycle.

Basal Body Temperature Charting

You may have tried charting, and given up in frustration - but I would urge you to reconsider. A set of BBT charts can help you to keep track of improvements in your cycle over time. They are also incredibly useful for your acupuncturist if they have advanced training in fertility acupuncture and will help them to fine tune their treatment and advice. 

The most important thing I am looking for in a chart is that it has a ‘biphasic’ appearance, the first half of the month should have temperatures  in the lower range (ideally around 97.5'F / 36.38'C) and the second half of the month should have temperatures that sit approximately 0.5'F / 0.3'C higher (over 98'F / 36.68'C). This gives a chart a classic biphasic appearance, which means there are two distinct phases of the chart corresponding to the follicular phase and the luteal phase, with the process of ovulation acting as the pivot between the two.

Taking your temperature

It is best to take your temperature at the same time each day, ideally following at least 3hrs sleep. If you have been disturbed in the night and went to the loo in the small hours of the morning, just note that you were up in the night, but take your temperature anyway. It is always worth noting things like a disturbed night, alcohol intake the previous night and medicines as they can alter your temperature. If you have noted these factors on your chart then you know that those temperatures might be slightly incorrect and it may be prudent to ignore them if they don't fit the pattern.

Taking your temperature vaginally is slightly more reliable – but whichever way you decide to take your temperatures, stick to that method for the duration of the chart.

If you are a shift worker with irregular sleep hours, it is best to choose a particular time of day to take your temperature and stick to the same time of day each day – just make a note on the chart about whether you were asleep or on shift prior to taking your temperature.

If you take your temperature at a different time of day, the following link may be useful - it is a webpage which calculates what your BBT would have been at the correct time:

Other things to note on your chart...

Cervix observations

The position and tone of your cervix within your vagina changes around ovulation. For most of the month, the cervix is lower, tightly closed and feels firm, a bit like the firmness of the tip of your nose. When you are imminently ovulating, your cervix becomes ripe and open; it will feel soft like your lips.

If you are one of the women who have less obvious cervical mucus, you should be able to track your cervical mucus changes more easily if you are also charting your cervix position on a regular basis because this is the area where you should still be able to find some cervical mucus.

Cervical mucus

You should make notes about any observations about cervical mucus on your chart, this information can be cross-referenced with your temperature information to confirm when you are likely to have ovulated.

Textbook cervical mucus changes:

  • After your period – dry
  • A few days later – milky, like a milky lotion
  • A few days later – wet and watery
  • A few days before ovulation – slippery and stretchy like egg white, designed to assist and nourish sperm
  • After ovulation – thick and sticky, designed to ‘plug’ the cervix opening

LH surge, OPK results

If you can, check your LH surge or oestradiol peak with an ovulation prediction kit (OPK) and make a note of the results on your BBT chart. You may wonder what is the point of charting and using an OPK but this additional layer of information can be really useful when it comes to interpreting the data from a chart.

Start checking for an LH surge about 5 days prior to when you think you ovulate. On your chart note both negative and positive OPK results (smiley faces, flashy faces or however your predictor kit displays results!)

Alcohol, stress, illness, medication, travel

If you have had a few drinks the night before, alcohol can cause temperatures to rise and behave erratically so it is worth noting this on your chart.

If you are having a particularly stressful time, have been unwell or taken any medication such as paracetamol or ibuprofen make a note on the chart; all of these things can have an effect on your basal body temperature.

A 'textbook' chart

Before explaining a textbook chart, I need to point out that this is just so you can start to work out what kind of issues you can look for in a chart. Few women have perfect charts, and you do not need a perfect chart in order to get pregnant - but a set of charts can help a fertility specialist to work out why you might not be falling pregnant and how to help you improve your fertility.

  • The temperature should drop as the bleed begins, and hold steady in the low range at about 97.5F /36.4'C, the temperatures should stay around this lower level for the first half of the cycle.
    Choppy temperatures in this phase can be caused by alcohol intake or stress, or can indicate a hormonal issue. It is worth noting on your BBT if you had alcohol the night before any of the temperatures taken.
  • At around ovulation there should be a small dip, then a strong surge upwards to the second phase of the cycle, the luteal phase. Temperatures should rise by approximately 0.5’F / 0.3'C and the temperature for the luteal phase should all be over 98’F / 36.68'C. Ideally this upward surge from lower temperature range to the upper temperature range should happen over 24-48hrs, if it takes 3 days to move from one phase to another that is too long. The shape of the curve at this point can provide additional information about how the hormones are behaving.
  • For the second half of the cycle, the temperatures should hover around 98'F / 36.68'C for around 12 days. If the temperatures are not sustained at the higher temperature for at least 10-12 days, it suggests that the body is struggling to maintain a sufficient level of progesterone. Youou may find it helpful to work with a Fertility Support Trained Acupuncturist to investigate this as there are several possible reasons for this to happen..

As I explained above, few women have a perfect chart and the aim of charting is not to achieve a perfect chart!

Charting is a fantastic tool to help identify areas of concern, in clinic it can help me to know which blood tests to recommend and how best to treat to support the cycle with acupuncture. There is so much in the way of nutrition, lifestyle and acupuncture that can be done to improve a chart, and any improvement in a chart is a movement towards a more fertile state.

I have uploaded a spreadsheet with a simple, basic chart for you to use - click here to access the Google Doc and please make a copy to use for yourself.

To read more about Alex, take a look at her listing here.

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