Basal body temperature is the lowest body temperature attained during rest. This temperature is taking upon waking and before any activity (I literally reach over to the nightstand and grab my thermometer without moving).

BBT is informative because it can help us understand our fertility. BBT fluctuates throughout the month due to the hormonal changes our bodies undergo. BBT can be tracked through specified thermometers (I found mine at Target) or devices (TempDrop has been recommended to me).

I started tracking my BBT right after I took my last hormonal birth control pill and had a good understanding of my body within 3 months (please note, everyone is different and might not have consistent data within 3 months).

I learned that my BBT will stay fairly consistent for the first 17-19 days of my cycle (day 1 of bleed to ovulation) then spike to a higher temperature. This temperature spike indicates ovulation (read--BBT cannot predict ovulation, but it confirms ovulation). The higher temperatures will remain for another 10-12 days which indicate a proper progesterone response.

The reason for the change in temperature is due to the change in hormones. The first part of your cycle (day 1 of bleed until ovulation) consists of higher amounts of estrogen, which is reflected in the lower BBT. When ovulation occurs, your BBT will spike because the corpus luteum begins to release progesterone which is the hormone needed to promote and keep a pregnancy. As long as your progesterone levels are healthy, your BBT will remain high for another 10-12 days until you start your period again (if pregnancy did not occur). At this point, your temperature will drop back down and you’ll know your period will begin.