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When you’re trying to start a family, it’s hard to be patient. But getting pregnant can take some time. Keeping track of your basal body temperature can help you understand your own fertility. You’ll be able to better predict when you ovulate. This can help you figure out when you have the best chance of becoming pregnant.

Here’s what you should know about tracking your basal body temperature if you’re ready for a baby, or you are trying to avoid getting pregnant.

Unlike ovulation kits you can buy at the store, tracking your basal body temperature won’t cost you anything. There are no side effects, either.

It’s important to understand that fertility isn’t the only thing that may influence your basal body temperature. These factors can also have an impact:

  • stress
  • sleep cycles that are interrupted, or getting too much sleep
  • shift work
  • illness
  • travel and changes in time zones
  • alcohol
  • gynecological disorders
  • some kinds of medications

Some women may also ovulate without their basal body temperature fluctuating at all.

Basal body temperature describes your temperature when you’re resting. Your basal body temperature can increase minimally when you’re ovulating. Women are at their most fertile in the two to three days prior to this temperature increase.

By keeping track of your basal body temperature, you can make an educated guess as to when you’re most likely to ovulate. Then you’re able to determine which days to have sex so you have the best chance to conceive.

Tracking your basal body temperature can also be useful if you’re trying not to become pregnant. By avoiding sex on days when you’re likely ovulating, you can reduce your chances of conception. But keep in mind, this method doesn’t provide sufficient warning. Always use a backup method of birth control to prevent pregnancy.

The process for basal body temperature tracking is simple, but it does require a small commitment.

  • Every morning before getting out of bed, you’ll take your temperature and note it on a chart. You can use a special thermometer designed for basal body temperature, or a digital oral thermometer. You can take an oral, vaginal, or rectal reading. Just be sure to use the same method each time.
  • Take your temperature as close to the same time every day as you can. That may mean you’ll have to set an alarm clock. You should try to stay within 30 minutes of your average time. You should have a minimum of five hours of sleep before measuring.
  • Plot the thermometer number on a chart. You can use a fertility tracking app, or track it yourself on graph paper. Over time, a pattern may begin to emerge. Look for a change in your recorded temperature of about 0.4 degrees over a 48-hour period. When this shift stays constant for three days or longer, it’s likely an indication of ovulation.
  • Plan to have sex on your most fertile days. About two days before you expect your basal body temperature to rise, you’ll be at your most fertile. Keep in mind that sperm can survive for up to five days inside your body. You should aim to have sex on your fertile days.
  • Be careful if you’re trying to avoid getting pregnant. If you’re tracking your basal body temperature to avoid pregnancy, don’t have sex from the first day of your period until several days after your basal body temperature number rises.

If your basal body temperature stays up for 18 days or longer after ovulation, you could be pregnant.

It can take a few months of tracking your temperature for a pattern to emerge. Be consistent about tracking for three to four months before using the data.

Speak to your doctor if you’ve been charting for a few months but your cycles are irregular and there’s no discernible pattern emerging. Likewise, ask your doctor for preconception advice if your patterns are regular, you’re having sex on what your chart indicates are the most likely days of fertility, and you haven’t become pregnant in three to four months.

You don’t need a special thermometer to measure basal body temperature, but there are options that can make reading your number as easy as possible.

Easy@Home Digital Oral Basal Thermometer

This thermometer is designed specifically for women trying to conceive. Features include an alarm clock, backlight for visibility in the dark, a sensitive measurement range, fever alarm, and test completion alarm. Free chart included.

Find it on Amazon.

Basal Body Thermometer by iProvèn

This highly accurate thermometer is designed for daily readings first thing in the morning. The thermometer tracks your last measured temperature, so you can record it on your chart whenever you like. It’s an actual body temperature thermometer, not a predictive thermometer. That means it may take longer as the probe adjusts, but it will produce the most accurate reading. Free charting table available for download.

Find it on Amazon.

iBasal Digital Thermometer

With an alarm clock, sensitivity to 1/100th of a degree, cycle day tracking, and graph population for your 10 previous readings, this thermometer is a well-rounded option. It will also help you interpret your thermometer readings so you can accurately predict fertility.

Find it on Amazon.

All you need to begin tracking your basal body temperature is a thermometer and some method of tracking your daily readings. Remember to be consistent. Take your temperature first thing every morning at the same time. Accuracy is very important.

After tracking one complete cycle, review your results. Chart for a few months so you can look for patterns. If you need help interpreting your records, there are many resources available online. Your doctor may also be able to help.