Basal temperature – what is it and how to measure?

What is basal body temperature (BBT), what is it used for and how to properly measure?

Basal body temperature (BBT) is temperature of the body in the state of rest. Its value isn’t always the same, it changes through menstrual cycle under control of the hormones.

In ovulation corpus luteum synthesizes progesterone which is responsible for raise of basal body temperature. It remains higher through whole luteal phase of menstrual cycle (phase from ovulation to next period). Before onset of the period corps luteum decays and progesterone levels drop and so does the basal temperature. In case of conception and implantation, basal temperature will remain higher since corpus luteum will continue to produce progesterone during first trimester of the pregnancy.

Basal body temperature should be measured right after awakening, after 6-8 hours of continuous sleep. Getting up, going to the bathroom or else will have an effect on basal temperature and graph won’t be reliable for detecting the natural temperature leap caused by progesterone.

For BBT measurements most convenient are thermometers with 1/100th of degree accuracy. This is important to detect the change in temperature of 0,2-0,5°C. Temperature leap will be registered most often day after the ovulation has taken place, so this method can detect ovulation within 3 days time frame. In rare cases corpus luteum can form a cyst that will continue to secrete progesterone even if pregnancy hasn’t occurred. This will cause higher values in measured temperature.

Measurements will also be unreliable in case of inconsistency in measuring, in case of infections followed by fever, under influence of certain medicinal products, especially hormones, in case of drinking alcohol day earlier and in case of stress, breastfeeding or insomnia.

Basal temperature measurement can be used as a method of planning of intercourses to achieve pregnancy, but also as a contraceptive method if a couple will abstain from sexual activity from the beginning of the cycle to the third day after the leap in basal temperature.