Basal Body Temperature (BBT)

If you are planning to conceive, or know someone who is, you might have heard of basal body temperature (BBT) charting. Your BBT is in essence your body’s core temperature when it is at rest. It is one of the many tools that we can use in fertility planning to assist us in ensuring that our cycles are on track. By studying the trends of our BBT over time, we can get to better know our bodies and how they are functioning.

The Menstrual Cycle

During a woman’s menstrual cycle a lot of hormonal changes are happening! These fluctuations predictably influence our core temperature and can give some insight into the functioning and balance of our hormones. Whilst these workings of the body are incredibly complicated, aspects related to temperature and menstruation can be simply discussed with two hormones in mind: oestrogen and progesterone.

The first half of the cycle is dominated by oestrogen. Oestrogen is important for maturing an egg in the ovary to be released at ovulation. Once ovulation has occurred, the remanence from where the egg was released secretes progesterone. This becomes the dominant hormone of the second half of the cycle and is necessary to build a thick       juicy uterine lining in the hopes of sustaining a life. If an embryo has not implanted, then this degrades and with it the drop in hormones triggers menstruation.

Tracking BBT

To accurately track BBT, your temperature needs to be recorded the same way at the exact same time every morning before getting up and moving around. Seems like a lot of hassle, right!? So why would anyone go to all the trouble?:

It can help you tell if you are ovulating. 

When most women ovulate there is an increase in temperature in the following days due to the surge in progesterone. There must be a sustained rise for at least 3 days to be sure that ovulation has occurred. In some conditions, such as PCOS, ovulation may not happen naturally, so this is a way to help see whether or not this is actually happening for you.

It can help you to determine when you are at your most fertile.

You are most fertile for the on the day of your temperature spike and the 2 days before this. so by tracking your BBT over a few cycles you will be more aware of your when your ideal window is. This information is helpful for making sure your partner does not schedule business trips around this time!

You can also use it to help avoid babies!

Some people use this method as a form of contraception. To avoid pregnancy, unprotected sex is off the table every menstrual period until 4 days after the BBT rise. Please be mindful that this technique is not 100% and that sperm can stay vital for up to 5 days in the reproductive tract. This method also does not protect you from STI’s.

Why just stop at temperature!?

You can add in other symptoms you may be experiencing such as food cravings, pain, emotions etc in order to give you a visual representation of patterns that might be unfolding. Other aspects to consider:

Your BBT can be influenced by other factors such as:

  • Illness
  • Stress
  • Interrupted sleep
  • Alcohol
  • Some medications
  • Certain gynaecological disorders.

It is not 100% diagnostic, but charting your BBT records important details to pass onto your healthcare professional or

fertility specialist in order to assist them to be able to provide the most comprehensive care possible.



Published on November 15, 2019