Basal Body Temperature (BBT) Chart
When planning a pregnancy, it is important to know if an egg is released from your ovaries each month. It also is important to know when the egg is released. That way, you can plan to have sex during that time. This will increase your chances of becoming pregnant.
Since your body temperature rises after you release an egg (ovulation), if you chart your temperature, it can tell you when you’re most fertile.
A basal body temperature (BBT) chart is a record of your temperature from day to day. To complete a BBT chart, you will take your temperature every morning at the same time using a special thermometer. Then you will mark your temperature in your chart.
A woman’s temperature is lower during the first part of her menstrual cycle. It rises sharply around the time an egg is released (ovulation) and stays relatively high for 2 weeks. A rise in temperature of 0.4 to 0.6 degrees or more in a 24-hour period usually means an egg has been released. Seeing this rise on your chart will let you know that you are fertile at that time. You may need to chart for a few months to see your ovulation pattern.
Cervical mucus method
A woman has changes in her vaginal fluids or cervical mucus when an egg has been released. Talk with your doctor or nurse about the cervical mucus method. It can be used with BBT charting to help pinpoint your most fertile time.
Charting your BBT
- Buy a basal body temperature thermometer (glass thermometers are best).
- Start charting on the first day of your menstrual period. A blank chart is attached to this sheet.
- Shake down the thermometer before you go to bed. Place it on a table near the bed.
- Take your temperature for 5 minutes each morning right after waking up. Do this before getting out of bed, smoking, eating, or drinking. Any activity may raise your temperature.
- Record your temperature on the chart by placing a black dot on the temperature line in the correct date column. (See sample chart.)
- Draw a line between yesterday’s temperature dot and today’s dot.
- Mark days you have sex by circling the dot.
- Change the temperature dot to a star if there is some other reason your temperature
might change: a cold, fever, a restless night, or medicine like aspirin, Tylenol, or Motrin, which are fever reducers.
- Start a new chart the day your period begins. Mark the days of your period with an “X.”
BBT charting can be unreliable
It is important to note that your BBT chart is not always a reliable way of telling if you have released an egg. Other factors, like illness or stress, can affect body temperature and ovulation. BBT charts work best if your body has very regular cycles.
If it is very important that you know if and when an egg is released, a urine test kit, called an ovulation predictor kit, works better. BBT also is not a reliable way to prevent pregnancy.
Reading the chart
According to the sample chart below, this woman ovulated on day 16 of her cycle (notice rise in temperature on day 17). The egg has only 24 hours to be fertilized, but sperm can live for 6 days in the uterus and fallopian tubes. This woman’s most fertile days would have been days 10 through 17. She had intercourse on 5 of those days, so her chances of becoming pregnant are good.
BBT charting can be difficult to understand. If you have any questions, be sure to ask your doctor or nurse.
Sample BBT chart
Charting your BBT
Make copies of the chart below, and use them to chart your basal body temperature.