Basal Body Temperature Method for Fertility

What is basal body temperature?

Basal body temperature method is included as one of the natural family planning methods which is also known as fertility awareness-based methods. It is the body temperature measured at rest, especially while sleeping. Usually it is the temperature measured immediately following awakening and before undertaking any physical activity.

During ovulationm the basal body temperature rises about one half to one degree Fahrenheit above the normal level. Thus serial measurement of basal body temperature is a way of knowing the time of ovulation. This in turn helps to locate the time period during which a woman has best chance of falling pregnant.

Regular charting of basal body may be used as a part of fertility awareness. This method helps to determine the most fertile days of the cycle in women who want to have a family. It can also be used by women who want to avoid pregnancy and are not using any other contraceptive methods. In this case this fertility awareness technique will help to determine the days when sex is to be avoided.

Why is it done?

Ovulation Date

Charting of basal body temperature is an inexpensive technique of determining a woman’s fertility status. The regularity of menstrual cycle is often regarded as evidence that a woman is ovulating at a regular interval and normally. An irregular menstrual cycle may be indicative of absent ovulation. However, in many women with a regular menstrual cycle there may still be absent or irregular ovulation whereas women with irregular menstrual cycle may actually ovulate at regular intervals.


Basal body temperature testing can even provide an early indication of pregnancy since home pregnancy tests may fail to provide accurate results within 2 to 3 weeks after ovulation. By using the approximate date of ovulation obtained from regular charting of basal body temperature, it helps a woman avoid false negative result owing to early testing. Elevated basal body temperature for 18 consecutive days definitely points towards pregnancy.

Gestational Age

Regular tracking of basal body temperature is also a comparatively accurate method of estimating gestational age of the growing baby than using menstrual periods. However, this is rarely necessary as ultrasound examination can provide a fairly accurate gestational age after 8 to 12 weeks depending on the equipment that is used and skill of the technician.

How to do basal body temperature charting?

Regular charting of basal body temperature does not require any special preparation. It is however, important to speak to a medical doctor about your recent childbirth history, stopping birth control pills or using other contraceptive methods, breastfeeding or progression of your age towards menopause.

The temperature should be measured every morning before getting out of bed. Digital oral thermometers or specially designed thermometers are used. At least 6 hours of uninterrupted sleep is required for accurate reading. Temperature can be measured orally, vaginally or rectally but whatever you choose, the same method should always be used for the most accurate results. Next, the measured temperature is plotted on a graph paper. The basal body temperature rises by about 1 degree Fahrenheit at the time of ovulation. Maintenance of this slightly high temperature for three days or more is indicative of ovulation.

Using temperature to decide on sexual activity

The most fertile period of the cycle is about 2 to 3 days before the basal body temperature rises. For women planning to fall pregnant this is the ideal time whereas those who want to avoid pregnancy should refrain from unprotected sex during this period. This technique cannot predict ovulation but rather indicate that ovulation has occurred. Furthermore sperm remains alive in the female reproductive tract for 5 days therefore the basal body temperature method may sometimes fail to prevent pregnancy. Other forms of birth control should therefore be considered.

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