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When trying to get pregnant, women will often track their basal body temperature to determine when they ovulate (i.e. when they release an egg from their ovaries).
Although this method is somewhat labor intensive, it’s a no-cost way to pinpoint your fertile window (the time of month you’re most likely to get pregnant).
What Exactly is My Basal Body Temperature?
It’s your body’s temperature at rest (before you become active for the day).
What’s the Relationship Between Basal Body Temperature and Ovulation?
When an egg is released during ovulation, the body produces a hormone called progesterone. The progesterone raises your body temperature. Therefore, your basal body temperature (BBT) increases right after ovulation.
How Do I Measure My Basal Body Temperature?
1. Take Your Temperature at the Same Time Every Morning When You Wake Up, Before Getting Out of Bed.
You can do this with a regular digital thermometer or with a more precise basal thermometer. Basal thermometers can be found at your local drugstore or online. Check out this popular option, this higher-tech option and this luxury ring option.
2. Log Your Temperatures Daily for at Least One Cycle (Ideally for Two or Three Cycles).
You can use a chart to track your temperatures or apps like the Femometer My Period Tracker or the Flo: Health & Period Tracker.
PediaTip: Always use the same thermometer when measuring your basal body temperature.
Why? Because there’s some variation among thermometers. In addition, measure your temperature the same way (via the mouth, the ear, etc.) each time.
What You Can Expect to Happen With Your Basal Body Temperature:
1. At the beginning of your cycle, your basal body temperature will probably read below 98.6°F (usually 97.5-98.2°F). This is because your progesterone level is low at this time.
2. One day before ovulation, your temperature will dip slightly because of a surge in luteinizing hormone (another reproductive hormone).
3. On the day after ovulation, progesterone levels spike, leading to an increase in basal body temperature above 98.6°F. You can expect your temperature to rise by about 0.3-0.5°F on this day.
4. If you DON’T get pregnant during the cycle, your basal body temperature will drop again just before your next period starts. This is due to a decrease in progesterone.
If you DO get pregnant during the cycle, you won’t experience this drop in your basal body temperature before your period. Why Not? Because your progesterone level will remain elevated.
The Bottom Line
Measuring your basal body temperature is a relatively inexpensive way to pinpoint your fertile window (depending on which basal body thermometer you purchase, if any). If you’re sick of tracking your basal body temperatures or you don’t want to deal with the hassle in the first place, try an ovulation predictor kit. Ovulation predictor kits can get pricey, but they’re accurate and easy to use.
