Basal body temperature is the temperature of your body at rest. If you monitor your basal body temperature, which varies in response to the hormonal fluctuations of the menstrual cycle, you can estimate the timing of ovulation each month. Your body temperature rises by a small amount (0.5 to 1.0 degree Fahrenheit) at the time of ovulation, and then stays elevated for several days, due to the rise in the level of the hormone progesterone. By abstaining from intercourse for several days surrounding the time of ovulation, you can dramatically decrease your risk of pregnancy.

To monitor your basal body temperature, take your temperature every morning as soon as you wake up. To get an accurate recording, your temperature should be taken at the same time every morning, before any activity, and before rinsing your mouth, washing your face or drinking any liquid. Record the first day of your period as day 1 when you track your temperature.

By recording your daily temperature in the form of a graph, you will see your temperature rise. You should record basal body temperature for a few menstrual cycles before relying on this method for birth control, so that you can more accurately determine when ovulation begins. Look for a temperature increase lasting at least three days, as this most likely indicates ovulation.

Practicing this method is relatively simple and requires a basal body thermometer, paper, a pen, time and attention. If you use a basal body thermometer, which typically marks the units from 96 to 100 degrees with markings for each one-tenth of a degree, rather than an ordinary thermometer, it will be easier for you to distinguish the minor temperature fluctuations associated with ovulation. A basal thermometer costs between $10 and $12 and is available at local drug stores.

Because it is difficult to determine the exact day of ovulation, this method is more successful when you don't have sex from the day your period ends until after the third day AFTER the rise in temperature.

Advantages

• Perfect use of this method results in a 2 per year pregnancy rate.
• Other than the cost of the basal body thermometer, this method does not cost anything, and there is no need for medications or surgery.
• This method does not interrupt or alter fertility. Pregnancy is possible as soon as this method is abandoned.

Disadvantages

• When used imperfectly, this method has a pregnancy rate as high as 84 percent.
• Because of normal variations in the menstrual cycle and in the lifespan of eggs (one to three days) and sperm (two to seven days), you will need to abstain from intercourse for a number of days, including those immediately around ovulation, to be safe.