Structure
Basal body temperature (BBT) is the term used to describe the temperature of the body upon waking each day. A special thermometer, called the basal thermometer, is made to be incredibly sensitive and to measure as accurately as possible. The thermometer comes in both a digital and standard glass model. Unlike glass thermometers, the digital basal thermometer is much more difficult to break. Modern glass models no longer contain the harmful element, mercury. Each night a woman should shake the element down in the glass thermometer to ensure that it is ready for use first thing in the morning.
Measuring
The basal thermometer is used by women to chart their BBT for predicting fertility. A user records her temperature in the morning before doing any other activity. It is most accurate if at least five hours of uninterrupted sleep precede the measurement. To obtain a measurement the thermometer is place under the tongue, into the vagina or into the rectum. The same location of measurement should be used every time.
The basal thermometer is accurate within .1 degrees Fahrenheit according to BabyHopes.com. This is .1 degrees more accurate than regular glass thermometers. It also records the temperature using the nearest two-tenths of a degree, unlike standard thermometers. The basal thermometer only takes 30 to 60 seconds to record a temperature. The temperature must be taken at close to the same time each day for accuracy.
Results
According to BabyHopes.com the body's temperature may vary by up to .2 degrees Fahrenheit per hour. Once the BBT is taken, you record the reading on a temperature chart. A shift of .4 degrees Fahrenheit occurs after ovulation, according to BabyHopes.com. According to the Mayo Clinic, continual charting of the BBT is necessary for at least three months before it can be used to accurately predict peak fertility.
Right before ovulation the BBT will be lower than at any other point during the month. Directly after ovulation the BBT will rise. In order to have the best chances of conceiving, a woman should engage in unprotected sex when her body temperature drops. The Mayo Clinic points out that sperm can live in the reproductive tract for up to three days. Women using the basal thermometer as a pregnancy prevention method need to take this into consideration. Unprotected intercourse should be avoided from the menstrual period until the night of the third day after the temperature rises.
