Basal body temperature & natural family planning

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How does basal body temperature work?

There is a link between ovulation and temperature, with a small (but significant) shift in basal body temperature, rising slightly after ovulation. This is due to an increase in the hormone progesterone. Basal temperature is measured first thing in the morning as soon as you wake up – before you sit up, talk, or get out of bed. Calculating hormone-driven temperatures when your body is fully at rest can help you pinpoint where you are in your cycle and find your fertile window (i.e. when you can get pregnant). 

What can affect basal body temperature?

Ovulation aside, there are a few things that can affect basal body temperature that are good to be aware of when using the temperature method for natural family planning:

• Sleep: Not getting enough sleep, or sleeping more or less than you usually do, can have an impact on your resting body temperature. 
• Alcohol: Consuming a few glasses of beer or wine can also elevate body temperature. 
• Sickness: Being unwell can cause a fever, which in turn affects the body’s resting temperature.
• Certain conditions: Such as hypothyroidism, can affect BBT, and those going through menopause may also experience fluctuations in basal body temperature due to hot flashes. 
• Some medications: Check with your doctor if you are regularly taking medication to find out if it could affect your BBT.

Natural Cycles is able to detect changes in temperature and can exclude a temperature if it is higher or lower than usual. The NC° algorithm works even if you’re experiencing the specific conditions mentioned above. Still, the app may extend your fertile window if it can’t identify your ovulation due to a varying temperature.

What is the difference between basal body temperature and body temperature?

The difference is when and how you measure your temperature. BBT is the baseline body temperature you get when you’ve just woken up from several hours of sleep. A regular fever thermometer can be used to measure body temperature at any time of the day. On the other hand, basal body temperature requires a special thermometer that measures two decimal places and is used in those crucial morning moments as your body awakens from rest.

How to use the basal body temperature method

Here is what you can expect when using the basal body temperature method:

• Measure your basal body temperature. You can use a special thermometer that shows two decimal places to measure your BBT. You should take your temperature first thing in the morning, as you need to capture the body’s lowest resting temperature before you get out of bed. If you're using Natural Cycles to prevent or plan pregnancy, you can also measure temperatures with a wearable device like an Oura Ring or Apple Watch. Wearable devices work a bit differently from a BBT thermometer, as they measure continually throughout the night. Their sensors can accurately and precisely track temperature data, which the NC° algorithm uses to determine your fertile days.

• Consistency is key. Measure your temperature with the same thermometer at the same time every day to ensure an accurate reading (i.e. regularly switching measuring devices may cause inconsistencies). Get at least three hours of uninterrupted sleep each night for the best results. If you have a bad night’s sleep or wake up at a much earlier or later time than usual, you should skip measuring the next day.

• Track your basal body temperature on a regular basis. Keeping track of basal body temperature shifts can tell you exactly where you are in your cycle, something you can’t know just by counting cycle days. Precision is useful if you’re looking for a hormone-free way to prevent pregnancy or want to find the days when you have the best chance of conceiving if you’re trying for a baby. At Natural Cycles, we recommend measuring at least five days a week. This helps give the algorithm plenty of data to narrow down your fertile window and give you more Green (not fertile) Days. If you're syncing your BBT with the NC° app, you can choose to exclude temperatures on days when you haven't slept well.

• Time when to have sex. Among other factors, a rise in temperature for several consecutive days is a clear indicator that ovulation has happened. If your BBT is between 97°F (36.1°C) and 97.5°F (36.4°C), you are most likely fertile. Since the egg cell can live for 24 hours and sperm can live up to five days, you should plan unprotected sex carefully, depending on whether you want to avoid or plan pregnancy. Basal body temperature will drop again if pregnancy doesn’t happen. This is an indication that your period is on its way, which signals the start of a new cycle.

Basal body temperature in early pregnancy

The BBT method can be used to detect pregnancy. One of the signs of early pregnancy is a consistently high basal body temperature that lasts more than 18 days following ovulation. Temperature typically dips right before our period during the menstrual cycle. However, in early pregnancy, the basal body temperature remains elevated. This is due to the raised level of the progesterone hormone, which stops the uterine wall from shedding and helps with implantation of the fertilized egg cell. If you think you might be pregnant, you should always take a pregnancy test or see a healthcare provider to confirm pregnancy. 

How the temperature method can help you predict peak fertility and get pregnant

You are at peak fertility in the days around ovulation. In terms of temperature, this means the best time to try to get pregnant is before your temperature rises. Regularly tracking your BBT can help you find your most fertile days. If you’re trying to start a family, the temperature method is an affordable and natural way that you can use to work out the best days to conceive. Natural Cycles’ temperature-based algorithm can help you accurately confirm your ovulation and get pregnant faster. 

What are the safe days to have sex using the basal body temperature method?

You can also use the basal body temperature method to prevent pregnancy. Keep in mind sperm can live for up to five days in the female reproductive tract. If you’re using the temperature method to avoid getting pregnant, it is important to plan sex carefully. In the days before your temperature rises, you will want to abstain from sex or use protection, such as condoms, during your fertile days.

Natural Cycles is backed by science

Natural Cycles is the only FDA Cleared fertility app powered by a temperature-based algorithm smart enough to help you prevent or plan pregnancy naturally. 

Here’s how it works: the NC °app calculates your fertile days based on daily temperature readings and other personalized biometric data, like ovulation test results and menstruation dates. Plus, it gives you the option to input and track cycle symptoms you may experience. While there are many apps available for tracking your cycle and fertility, Natural Cycles is the only one that is 93% effective with typical use, and 98% effective with perfect use at preventing pregnancy. And is just as effective if you exclude a temperature or forget to measure. NC° removes human error, making natural family planning easier. 

Ready to take the guesswork out? 

FAMs have been around for decades, but what we do is different. With Natural Cycles, there’s no training or monitoring phase required. Plus, tracking cervical mucus is optional (and easy with our symptom-tracking features!). And thanks to our integration with Apple Watch and the Oura Ring, measuring has become even easier. There’s never been a better time to join! Save yourself the time and effort of counting calendar days and charting yourself, instead why not give Natural Cycles a try?