Natural Cycles is a regulated medical device for both birth control and pregnancy planning. It is cleared by the FDA in the US, CE marked in Europe, listed in the ARTG in Australia, and listed in the SMDR in Singapore.
This article will cover the following sections describing how Natural Cycles works:
- The menstrual cycle
- Fertility based on your unique menstrual cycle
- How to use Natural Cycles
- NC° Birth Control
- NC° Plan Pregnancy
Natural Cycles comes in the form of an app and a digital thermometer. The intelligent algorithm behind the app analyzes a user's basal body temperature (BBT) and Luteinizing Hormone (LH) data to identify the fertile and non-fertile days in each cycle.
Natural Cycles is 93% effective with typical use and 98% effective with perfect use, and it is effective from the first day of use.
By measuring and logging your BBT in the morning as outlined in our instructions for use, the algorithm gets to know your unique menstrual cycle. Based on your individual data, the app provides you with a daily fertility status.
For NC° Birth Control users, the fertility status is displayed in either red or green, where red indicates the days where you may be fertile and should use protection or abstain from intercourse. When your daily status is green, you are not fertile and don't need to use protection.
For NC° Plan Pregnancy users, the fertility status is also displayed as red or green with red days displayed as a color scale ranging from light pink to dark red on the fertile days. Darker red indicates your most fertile days, green is displayed non-fertile days, and brown on days where more data is needed.
When you start using Natural Cycles, it can take 1-3 cycles for the algorithm to get to know your unique cycle, resulting in a greater number of red days for NC° Birth Control users and brown days for NC° Plan Pregnancy users.
The menstrual cycle
The menstrual cycle consists of three phases: the preovulatory (follicular) phase, the ovulatory phase, and the postovulatory (luteal) phase. Each person’s cycle varies in length, and a new cycle begins with the first day of menstrual bleeding.
Each person has a unique menstrual cycle pattern. For example, the cycle length, the day ovulation occurs, the base temperature in the follicular and luteal phases, how much the temperature increases, and the overall shape of the temperature evolution throughout the cycle are all parameters that vary from person to person.
- The follicular phase is estrogen-rich and cooler. The average follicular phase temperature for our Cyclers is 36.23°C (97.21 °F).
- The ovulation day is when an egg (oocyte) is released from the ovaries and can be fertilized by sperm (however, the fertile window is six days due to sperm survival - read on to learn more about the fertile window). Two well-known biological indicators of ovulation are a temperature rise of 0.25-0.45 °C (0.4-0.8 °F) and a rise in luteinizing hormone (LH) roughly 48 hours before ovulation. The average ovulation day for our Cyclers is CD 18.
- The luteal phase is where progesterone dominates and ‘warms’ the body. The average luteal phase temperature for our Cyclers is 36.58°C (97.84 °F).
The fertile window is six days in the cycle. It ends with ovulation day and begins 5 days before, as sperm can survive up to 5 days in the body under the right conditions. Only during these six days is it possible to get pregnant through unprotected sexual intercourse. Below is an example of what a graph may look like for a NC° Birth Control user. This in-progress cycle shows the fertile window surrounding ovulation. The fertile window for this cycle is ten days long. This is because NC° Birth Control users will likely to get more than six red days per cycle to account for cycle and temperature irregularities:
After ovulation (in the luteal phase), the progesterone level in the body increases, which causes the basal body temperature to rise. Measuring the BBT is an indirect measurement of the progesterone levels in the body. Since the temperature stays elevated (compared to the follicular phase) from ovulation until the end of the cycle, it is a constant and certain indicator that the individual is not currently fertile.
Therefore, the temperature rise is the most important indicator to confirm that ovulation has occurred in the cycle. If the algorithm finds a sustained temperature rise, it confirms ovulation occurred in that cycle.
When a new cycle starts, the temperature drops back down to the follicular phase temperature range during menstruation.
Fertility based on your unique menstrual cycle
Charting body temperature is not a new form of birth control or fertility method. However, Natural Cycles pairs this traditional method with an algorithm that learns the pattern of your unique cycle to predict your fertile window. Natural Cycles can accurately capture every unique cycle by taking cycle irregularity, temperature fluctuations, recent usage of hormonal contraception, ovulation day variation, sperm survival, and several other essential factors into consideration.
Natural Cycles uses BBT data, period data, and optional LH data to calculate a daily fertility status. This fertility status is used to help Cyclers either prevent pregnancy using NC° Birth Control or plan a pregnancy using NC° Plan Pregnancy.
How to use Natural Cycles:
- Measure temperature - you should measure your BBT using the Natural Cycles thermometer each morning when you wake up before you get up for the day. It's okay if you miss a day here and there! However, the more often you measure, the better the fertile window will be isolated, and the more green days you will get. We recommend that you try to measure at least 70% of the mornings, or 5 out of 7 days in the week.
- Add data - enter your temperature data and, when relevant, period data (this lets the algorithm know when a new cycle starts and helps it find your ovulation). Natural Cycles will analyze your unique cycle and identify your daily fertility status.
- Learn your fertility - depending on where you are in your cycle, you’ll either be given a green day (not fertile) or a red day (fertile). You’ll need to use additional contraception like a condom or abstaining from sex to prevent pregnancy on red days. The algorithm defaults to giving red days if there is not enough information to confirm that you’re not fertile. This is why it’s important to provide the data points – temperature and period data – for the algorithm to give more green days.
There are three ways to use Natural Cycles: NC° Birth Control, NC° Plan Pregnancy, and NC° Follow Pregnancy. Please follow the following links to read more about the specifics of the Natural Cycles mode you’re looking to use.
NC° Birth Control
To use NC° Birth Control, you need to measure your BBT, input your data, and then the Natural Cycles algorithm will provide your daily fertility status. Your fertility status will show as either a green day or a red day. Green days mean that you’re not fertile. On red days, there’s a chance that you are fertile, and you should abstain or use condoms during intercourse.
When using NC° Birth Control, in addition to seeing your daily fertility status, you can add extra information like cycle symptoms, changes to your mood, and sex data so that you can learn even more about the pattern of your unique cycle.
You will also be able to log LH test results, which, although optional, may lead to higher ovulation day accuracy and more green days. 24-48 hours prior to ovulation LH levels surge, triggered by the increase in levels of estrogen in the body. Therefore, your levels of LH can be a good indicator of the most fertile days in the cycle. LH tests measure the level of LH in the urine and can be bought in the app, webshop or your local pharmacy.
Below is an example of where you can log your cycle symptoms each day, changes to your mood, and log if you took an optional LH test:
Below is an example of the graph that lets you compare what you've logged over time:
To help you learn more about your body, the app can also send you reminders. For example, if you are using the PMS trackers in the app, you can receive PMS alerts. You can also get reminders about when to carry out a breast exam as shown below:
New users and NC° Birth Control effectiveness
If you’re a new user of NC° Birth Control, it’s important to note that NC° Birth Control is effective from the first day of use. For the first cycles, when the algorithm doesn't have much information on when you usually ovulate and how much that varies, the buffer of red days at the beginning of the cycle is greater.
The more you add data over time, the more green days the NC° algorithm will be able to produce - as it will only produce a green day if it has enough information to confirm that you are not fertile. You will be given red days if the algorithm is uncertain. For a more detailed explanation of the NC° algorithm, please continue reading here.
What about irregular cycles?
Thanks to all the data you add to the app, Natural Cycles will get to know you and your unique cycle and adapt accordingly. You may experience more red days if you have irregular cycles, but the algorithm's effectiveness is the same.
Green days before ovulation
You will get green days (non-fertile) before ovulation until the algorithm deems it possible that you could be approaching your fertile window. At that point, you will be given red days until the algorithm is able to confirm that you have ovulated. The NC° algorithm uses your past ovulation pattern combined with statistical analysis to determine the fertility status at the beginning of your cycle. The NC° algorithm will give a buffer of red days before the predicted ovulation based on several factors like sperm survival probabilities, your personal ovulation pattern, how regular your ovulation pattern is, and how much data has been collected from past cycles.
Important tips to remember when using NC° Birth Control:
- Make sure that you’ve selected the NC° Birth Control mode. NC° Birth Control and NC° Plan Pregnancy work slightly differently. Detecting ovulation is the same for both products, but there are differences in the risk profile. For NC° Birth Control, the algorithm is optimized to have a very low risk of wrongly attributing a green (safe) day in the fertile window. In contrast, NC° Plan Pregnancy is optimized to better isolate the fertile window and the most fertile days. While using NC° Birth Control, the user gets either green (non-fertile) or red (use protection) days. On the other hand, NC° Plan Pregnancy users get a fertility scale ranging from green (not fertile) to the darkest shade of red (peak fertility). In short, if you’re looking to prevent pregnancy, make sure that you’re using NC° Birth Control which is set up to help you prevent pregnancy.
- If you’re coming from hormonal contraception, you must finish that before starting using NC. The hormones in the hormonal contraception you’re taking, whether it's the pill, patch, shot, or hormonal IUD, usually work to inhibit ovulation. Please refer here to when you can start using NC° Birth Control when coming from your specific hormonal contraception.
- Check your fertility status each day in the “Today view”. Predictions update each day with new data. For instance, the NC° algorithm initially makes predictions based on previous cycle lengths, but the predictions are updated after ovulation has been detected in the current cycle to give more accurate period predictions, using the ovulation date in the current cycle and your personal luteal phase length. Therefore, checking your fertility status in the “Today view” before intercourse is necessary to prevent pregnancy.
- Use additional contraception (we recommend condoms) or abstain from sex on red days. We regularly follow up on actual data from real users to monitor the product’s effectiveness and the algorithm’s performance. This is part of the post-market surveillance that we need to do as a certified medical device manufacturer for contraception. Every month we look at the effectiveness, unintended pregnancies, and the reasons behind the pregnancies. The most common reason for pregnancy using Natural Cycles is unprotected sex on a red day.
NC° Plan Pregnancy
To use the NC° Plan Pregnancy, you need to measure your BBT, input your data, and then the Natural Cycles algorithm will provide your daily fertility status. In NC° Plan Pregnancy, the fertile window is presented in a scale of red colors, where the most fertile day has the darkest shade of red, and the lightest red color indicates that fertility is unlikely. (See picture below to see the scale of colors in the Calendar/Month view.)
The brown days are days where more data is needed for the algorithm to provide a fertility status. Brown days mean that you need to keep measuring for the coming days. Non-fertile days are presented in a light green color.
There are 2-3 days per cycle in which you have the highest chances of conceiving (around ovulation day), even though the fertile window is six days in total. Ovulation day is the phase of the menstrual cycle when an egg (oocyte) is released from the ovaries and can be fertilized by sperm. To increase your chances of conception, the Natural Cycles algorithm can find your ovulation day and the days when you are the most likely to get pregnant by analyzing BBT and optional LH levels. Natural Cycles gives you the information you need to time intercourse and maximize your chances of conceiving. Our research shows that, on average, users take three cycles or less to become pregnant using NC° Plan Pregnancy. Source
The graph view is helpful to get an overview of your temperature data. The red color changes according to your fertility.
When using NC° Plan Pregnancy, in addition to seeing your daily fertility status, you can also add extra information like cycle symptoms, changes to your mood, and sex data so you can learn even more about the pattern of your unique cycle.
You will also be able to log LH test results, which, although optional, may increase the chances for the algorithm to narrow down your most fertile days. 24-48 hours prior to ovulation LH levels surge, triggered by the increase in levels of estrogen in the body. Therefore, your levels of LH can be a good indicator of the most fertile days in the cycle. LH tests measure the level of LH in the urine and can be bought in the app, webshop or your local pharmacy.
Below is an example of where you can log your cycle symptoms each day, changes to your mood, and log if you took an optional LH test:
To help you learn more about your body, the app can also send you reminders, like when it's time for a breast self-exam.
New users and NC° Plan Pregnancy
If you’re a new user of Natural Cycles, it’s important to note that for the first cycles, when the algorithm doesn't have much information on when you usually ovulate and how much that varies, the algorithm will give a broader range for your fertile window. However, if you measure your daily temperature and input your data regularly, this window will narrow after 1-3 cycles. For a more detailed explanation of the NC° algorithm, please continue reading here.
What about irregular cycles?
Thanks to all the data you add to the app, Natural Cycles will get to know you and your unique cycle and adapt accordingly. Cyclers with irregular cycles may experience more brown days because of a larger variation in the ovulation day. This just means there will be a larger window during which you should attempt to conceive in your cycle.
Important tips to remember when using NC° Plan Pregnancy:
- If you’re coming from hormonal contraception, you must finish that before starting using NC. The hormones in the hormonal contraception you’re taking, whether it's the pill, patch, shot, or hormonal IUD, usually work to inhibit ovulation. Please refer here to when you can start using NC° Plan Pregnancy when coming from your specific hormonal contraception.
- Check your fertility status each day in the “Today view” and do not trust future predictions as guaranteed outcomes. On the Month tab, you can see a monthly prediction of your coming cycle; this can range from 1-5 cycles based on your cycle regularity. Remember that future days in the Month tab are a forecast based on your historical data and are subject to change. Please make sure you always check the “Today view” to see your daily fertility status.