If you’re trying to get pregnant — or attempting not to get pregnant — it’s important to understand your body and its natural cycles. One of the ways to get some additional insight is by tracking your basal body temperature.
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Ob/Gyn Laura Detti, MD, explains what basal body temperature tracking is and how you can decide whether it’s the right move for you.
What is basal body temperature?
Basal body temperature refers to your body’s temperature when it’s fully at rest. Your basal body temperature increases just after ovulation, so tracking it can help you identify which days you’re ovulating. This can, in turn, tell you which days you should have sex if you’re trying to conceive (or which days to abstain, if you’re trying to stay child-free).
“It’s good to understand your cycles, to understand whether you’ve ovulated or not, and to see how long your luteal phase is — the second part of your menstrual cycle,” Dr. Detti says.
Most women’s basal body temperature is between 97 to 97.5 degrees Fahrenheit before ovulation; after ovulation, it typically ranges from 97.6 to 98.6 F. But other factors can impact basal body temperature, too:
- Lack of sleep.
- Having sex.
- Drugs and/or alcohol.
- Lack of sleep or interrupted sleep cycles.
- Some medical disorders and medications.
Everyone’s standard basal body temperature is different, and tracking it over the course of a few months can help you figure out yours — both before and after ovulation.
Why track your basal body temperature?
Whether you’re trying to get pregnant or trying not to, there’s value in knowing your cycles, Dr. Detti says. And showing your tracking results to your gynecologist or a reproductive endocrinologist can signal hidden health problems.
“Sometimes women’s basal body temperature has been going up and down up and down without a real marker of a changing point,” she says. “Those women typically do not ovulate — so those results spark an inquiry to start testing.”
How to take basal body temperature
There’s one key rule to keep in mind when tracking your basal body temperature: “You need to take it under the same conditions every day,” Dr. Detti says. “Typically women take their basal body temperature in the morning before getting out of bed so that every day it’s consistent.” Here’s how to do it:
- Take your temperature: Before you get out of bed to pee, put in your contacts, or even hit that snooze button, use a standard thermometer to take your basal body temperature orally.
- Record your results: Jot down the number in a journal, on a chart, or in whatever form you prefer. Some people use graph paper, while others use charting apps specifically designed to track basal body temperature.
- Be consistent: Record your basal body temperature daily (or as often as possible), attempting to take it at the same time every day. Skip tracking when you’re traveling or if you were drinking the night before, as your results will be skewed.
- Watch for a rise in temperature: Keep an eye out for an increase of about 0.4 degrees. When your temperature has stayed at this increased level for three days, you’ve likely ovulated and moved into the second phase of your menstrual cycle.
When to have sex (or not)
That slight increase in temperature happens after you’ve ovulated, but your body is most fertile right before you ovulate. Once you’ve gotten the hang of charting your basal body temperature, you should be able to identify patterns that will tell you how many days into your cycle you ovulate — and if you’re trying to get pregnant, you’ll want to have sex in those days just before ovulation.
“If a woman has regular cycles, after charting for a couple of months she knows when her temperature will rise and knows to have intercourse a couple of days before that happens,” Dr. Detti says.
The downside to tracking basal body temperature
There’s a catch: “Tracking your basal body temperature tells you about ovulation only after ovulation occurs,” Dr. Detti says. “It doesn’t give you any alarms saying ‘Hey, you’re about to ovulate.’”
This means that by the time your temperature rises, your fertile window has already passed.
Tracking your basal body temperature over time can help you gain a deeper understanding of when your body is likely to ovulate, but if you want a more straightforward answer about when to have sex in order to conceive, Dr. Detti recommends ovulation test strips instead. They react to your urine to tell you whether you’re within your fertile window.
“Typically women track their basal body temperature because their primary gynecologist tells them to do it to understand more about their cycle,” Dr. Detti says, “but the function of body temperature ends there — just to help you understand your cycle.”