Basal body temperature, or BBT, is the lowest body temperature that a person has on any given day. Throughout your cycle, your BBT will change based on fluctuations in your hormone levels, specifically the hormone progesterone.
Understanding BBT and your fertile window
Changes in basal body temperature can signal that you’re about to ovulate or that you just ovulated. Typically, BBT will dip to the lowest point right before you ovulate, and spike to the highest temperature in the two to three days following ovulation, with a big spike about 12 to 24 hours after ovulation.
This spike is caused by the sudden increase of the hormone progesterone in your system. After ovulation, progesterone is released by the matured ovarian follicle (now known as the corpus luteum). This hormone plays a big role in preparing the uterus for pregnancy, and in maintaining pregnancy if you do get pregnant. It also increases your body temperature, which will stay high throughout pregnancy if that egg gets fertilized, or lower back to normal if the egg is not fertilized and you do not get pregnant.
Having intercourse in the days before you ovulate is one of the best strategies for getting pregnant. Unfortunately, the biggest spike in BBT happens after you ovulate- but it can let you know that you’ve just ovulated, which is helpful when figuring out the pattern of your menstrual cycle. Even though it can be harder to track because it’s more subtle and the temperature doesn’t change as much, the dip in BBT can let you know that ovulation is just around the corner. Overall, tracking BBT can help you get a better sense of your fertile window from month to month.
How do I track it?
Since BBT is the lowest temperature your body reaches in the normal course of the day, follow these steps to get the most accurate results:
- First, you’ll need a thermometer that reads to 2 decimal places (for example: 98.34℉)
- Keep your thermometer by your bed
- Take your BBT as soon as you wake up – don’t get out of bed first and warm yourself by walking!
- Try to take your BBT at the same time each day
- Know that you may get an inaccurate result if you’ve been up late, slept in, or are sick
- If you do shift work or sleep odd hours, talk to your provider about the best time of day to take your BBT, or use another method of tracking
- Log your BBT in Ovia by clicking here!
