Basal Body Temperature (BBT)


If you’re trying to get pregnant, understanding your ovulation cycle can greatly increase your chance of conception. While you will have to use a fertility monitor or understand and chart changes in cervical mucus or luteinising hormones (which can be determined with an ovulation test) to predict when you will ovulate before it occurs, you can verify whether or not you are ovulating by charting your Basal Body Temperature (BBT).

Your Basal Body Temperature is simply the lowest temperature your body reaches while you sleep. The significance this holds to your ovulation is that when ovulation occurs, your core body temperature rises about half a degree and stays elevated for about 1 week. By consistently monitoring your BBT you can effectively determine whether or not you are ovulating simply by the natural shift in body temperature.

Checking your Basal Body Temperature and understanding the changes that occurs during ovulation is crucial to increasing your chances of pregnancy, but is quite simple once you know what you’re doing. Here are 8 things you need to know about checking your BBT:

  1. Purchase a thermometer specifically designed for checking your basal body temperature. These thermometers will be extremely precise and need to show at least to the tenth degree. Start recording your temperature during the first day of your menstrual cycle.
  2. Whether you decide to check your temperature rectally, vaginally, or orally make sure you check it the same way every time with the same thermometer.
  3. It’s important that you check your BBT immediately after waking. Do not make any physical movements; don’t eat or drink anything; do not smoke before checking your temperature; don’t even get out of bed.
  4. Always take your BBT around the same time every morning—there is a 30-60 minute window that’s allowed, but try to keep it as close to the same time as possible.
  5. Make sure you get enough rest; your body needs time to enter a deep, restful sleep so that your temperature can reach its lowest point. Plan to rest at least 4 hours before taking your BBT.
  6. Don’t make any changes to your temperature. You may be tempted to raise or lower it because you took it too early or too late but listing it exactly as it was is important. It’s also important to note that drinking alcohol or getting too little sleep can have an impact on your BBT, so avoiding alcohol before bed and getting as much rest is important.
  7. Always write down your results. There’s usually a small chart that comes with your thermometer for recording temperatures; don’t rely on your memory as you could forget or get mixed up from one day to the next.
  8. To determine if you are ovulating you will need to establish your coverline. The coverline is simply a line that will allow you to represent the time of ovulation. If you see a spike in your temperature that is more than two-tenths of a degree and lasts at least two days, you can begin your coverline—you are most likely ovulating during this period. Once your temperature goes back down to what it was during our menstrual cycle, you are no longer ovulating.