Since a woman has a limited number of days that she can get pregnant a month — typically around five — knowing your menstrual cycle and when you’re ovulating can increase your odds of getting pregnant, or not, if you’re using the method to avoid pregnancy. Fertility awareness is the first step in determining when you are most fertile, and the Basal Body Temperature, or BBT method, is one of many tools in the arsenal available to you.
The basal body temperature is the body’s lowest, resting temperature of the day, and is typically measured in the morning. As ovulation nears, the body’s BBT drops, then spikes with ovulation. The temperature remains higher, facilitating a fertile environment, until the next cycle begins. Two main hormones contribute to this temperature shift: estrogen, early in the cycle helps to lower the body’s temperature, and then increasing levels of progesterone prompt a rise in temperature. When tracked over a month, or several months, the BBT method can help you determine the unique pattern of your cycle.
This temperature increase is very slight, so you should be sure to use a basal body thermometer to track your fertility. While you can use a traditional glass thermometer, digital basal body thermometers are preferred for their ability to read differences of up to 1/100th of a degree. This is particularly useful because the variance in your BBT throughout the month may only be .4 to .6 of a degree F. Depending on how fancy the basal body thermometer is, it may beep when the highest temperature is reached and it may display a memory of the last reading. You can record your daily BBT on a simple piece of graph paper, or download a BBT method chart online.
Start taking your BBT on the first day of your period, as soon as you wake up. Keep the thermometer by your bed and take it before you take a drink or eat, and even before you get out of bed. Any physical activity or eating can raise your temperature. Keep in mind that you’ll register the biggest spike once you’ve already ovulated, so the first month may not help you all that much in determining the days you are most fertile. Over several months, the BBT method should hopefully give you a pattern that you can use to predict your ovulation, and as a result, the days you’re most likely to get pregnant. If you are using the BBT method as a means to avoid pregnancy, remember that this will not be the most effective method, and consider using it in conjunction with another form of protection.