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Basal Body Temperature (BBT) Charting

Topic Overview

The basal body temperature (BBT) is a person's at-rest temperature. Women can track their BBT to find out when they are ovulating. With this time line, a woman can learn when she is most and least likely to become pregnant.

When are you most likely to become pregnant?

About 2 weeks before your period you will ovulate, which means that one of your ovaries has released an egg. You are most likely to get pregnant on the day of ovulation and the 5 days before it.

When are you least likely to become pregnant?

Your egg is fertile for about 12 to 24 hours after you ovulate. Avoiding sex until several days after ovulation may help you prevent pregnancy. Keep in mind that your cycle can change, making it hard to know when you are ovulating. Some women use this information as a form of birth control. But it isn't very reliable for preventing pregnancy.

How can you predict when you will ovulate?

Your body temperature dips a bit just before your ovary releases an egg. Then, 24 hours after the egg's release, your temperature rises and stays up for several days. Before ovulation, a woman's BBT averages between 97°F (36.1°C) and 97.5°F (36.4°C). After ovulation, it rises to 97.6°F (36.4°C) to 98.6°F (37°C).

You can track your cycle by taking your BBT every morning. Take your temperature at the same time every day before getting out of bed. Next, record the results on a chart. If you have a somewhat regular cycle, the chart will help you predict when you will ovulate next.

What tools do you need to take your basal body temperature?

The change in your body temperature is very slight, so you need to use a special thermometer. You can use a regular digital thermometer or buy a basal thermometer. A basal thermometer shows you the temperature in tenths of a degree. This allows you to note tiny changes in body heat. This thermometer is faster and more exact than a regular thermometer.

Use a simple Fahrenheit temperature chart (What is a PDF document?) or Celsius temperature chart (What is a PDF document?) to track your temperature for several months.

Where can you get a basal thermometer?

You can find a basal thermometer or digital thermometer in a pharmacy or in the pharmacy section in many grocery stores. You can also find kits that include materials for measuring and charting BBT. These items are low in cost.

Credits

By Healthwise Staff
Primary Medical Reviewer Sarah Marshall, MD - Family Medicine
Specialist Medical Reviewer Femi Olatunbosun, MB, FRCSC - Obstetrics and Gynecology
Last Revised December 8, 2011

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