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How To Take Your Basal Body Temperature (BBT)

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Updated June 10, 2012

Your BBT, or basal body temperature, is your temperature first thing in the morning after several hours of rest. By charting your BBT for a few menstrual cycles, you may start to see patterns which will help you determine when you are ovulating.

Keep in mind that if you have PCOS, you may not ovulate regularly. This is one method you can use to help you determine if you are ovulating.

Your BBT tends to be lower in the first phase of your cycle, known as the follicular phase. At and after ovulation, your BBT can raise by as much as a half a degree.

Difficulty: Easy
Time Required: Less then 5 minutes every morning

Here's How:

  1. You will want to take your BBT at the same time each morning. Make sure to use a BBT thermometer, or a thermometer that will measure to the nearest tenth of a degree.
  2. Take your BBT first thing in the morning, before you get out of bed, go to the bathroom or even sit up. Start on day one of your menstrual cycle, and continue every morning until your next period.
  3. Chart your temperature on a BBT graph, or make your own.
  4. After you have charted for an entire cycle (one menstrual cycle to the next), take a look at your chart. You are looking for 3 consecutive days of higher than average temperatures. Sometimes you may see a slight temperature drop right before the rise. That drop tends to indicate ovulation.
  5. The rise in temperature is a sign that you have ovulated and are in the luteal (second phase or after ovulation) phase of your menstrual cycle.
  6. Use the information that you obtain to better predict your fertile days. For example if you see over the course of a few months that you tend to ovulate on day 15, 18 and 14, you may want to have sex on days 12 through 18 or 19.
  7. If you do not see the temperature change, try monitoring for a second or even a third month. You can use this technique in conjunction with an ovulation predictor kit if you are not sure when or if you are ovulating.
  8. If you still are not able to see a pattern, make an appointment with your gynecologist and bring your charts with you to show the doctor.

Tips:

  1. Set an alarm clock to make sure you wake and take your BBT at the same time. Your temperature can vary by a few tenths of a degree each hour. By measuring at the same time, you are ensuring the most accurate results.
  2. Keep your chart, pen and thermometer by your bedside so that you don’t have to get out of bed to get it.
  3. Also mark the days you have sex, changes in cervical mucus and results of ovulation predictor kits (if applicable) on your graph.
  4. Make sure to use the same thermometer throughout the entire cycle.
  5. You should have had at least 3 hours of uninterrupted sleep before you take your temperature. Otherwise the reading may not be accurate.

What You Need

  • BBT graph
  • Thermometer
  • Pen
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