Fertility Tracking

By Sophie Knapp I B.S. M.S.

Reviewed by Emily Reeves I PhD. CNS.

Fertility tracking is the use of physical and hormonal markers to identify a woman’s fertile window. Cycle tracking apps use physical changes that occur during the cycle while fertility monitors directly track hormone levels in the urine to identify the fertile window.

Cervical Fluid & Basal Body Temp

Cycle tracking apps predict the fertile window based on physical changes that happen to a woman’s body throughout their cycle. Many of these apps encourage you to track physical changes like sex drive, mood, cramps, acne, bloating, and cravings that are not reliable indicators of the fertile window. This is an important concept to be aware of when trying to prevent pregnancy. The two parameters which have the most evidence as reliable indicators of ovulation are cervical fluid consistency and subtle shifts in basal body temperature.¹⁰ Using these two measures to identify the fertile window is commonly referred to as the sympto-thermal method. This is considered to be the most non-hormonal-based reliable form of natural birth control method.⁵

We strongly recommend at minimum tracking your cervical fluid and basal body temperature if you seek to avoid pregnancy. If you are the type of person who likes to have multiple layers of accuracy, you can make the predictions more robust by also tracking levels of Luteinizing Hormone (LH).

Recommended Apps

Of the literal myriad cycle tracking apps out there, our favorites are Flo, Kindara, and Clue. They are all available on iPhone and Android phones through either the app store or Google play store. You can track cervical fluid and basal temperature for free in all three apps, though in Flo and Clue you have to add these parameters to the symptoms list as they are not included in the default list. Keep in mind that many of these apps are overall geared toward helping women better understand their bodies, so they emphasize tracking all the changes you experience throughout your cycle. As mentioned previously, many of these factors can be empowering to learn more about to get to know how your body works but remember that when it comes to accurately predicting the fertile window the most reliable measures are cervical fluid and basal temperature.

What to expect and why

So what are the changes you are looking for in cervical fluid and basal body temperature? Prior to ovulation, consistency and color of cervical fluid excretions is the strongest indicator as to whether or not sperm will be able to survive and swim to an egg. Fertile cervical fluid is alkaline and protects the sperm from an otherwise acidic vagina. As you approach ovulation, remember that estrogen is reaching its peak, and this typically causes cervical fluid to become increasingly wet, stretchy, and clearer as opposed to milky white or yellow.⁵ These changes help sperm move through the vaginal canal in order to reach an egg, and it’s usually observable if you pay close attention. Following ovulation, your waking temperature, referred to as basal body temperature, is another key predictor of your fertile window. Recall that following ovulation, a woman begins producing significantly more progesterone, which causes her body temperature to rise. So, an increase in temperature indicates that ovulation occurred the day before. A woman’s temperature will typically remain elevated until she begins menstruating again, which is also when progesterone production drops off.⁵

Accuracy of sympto-thermal method

Just how accurate are these measures at validating the fertile window? One study published in Reproductive Endocrinology tested the differences in accuracy of observing basal temperature and cervical fluid for predicting ovulation. They compared those methods with highly accurate ultrasonography to determine ovulation. The research team reported that cervical fluid observation showed no statistical difference in its ability to predict ovulation compared with ultrasonography and that basal body temperature measurements could consistently predict ovulation a day before ultrasonography could.⁶^,⁷ That’s great news as it means cervical fluid observations and basal temperature tracking are just as, if not even more accurate than some of our most technologically advanced and accurate methods for predicting ovulation. Also, tracking LH levels with test strips would add a third layer of data to better inform the time of ovulation for avoiding pregnancy. We’ll explain more about this in the next section.

When do I need to use a physical barrier?

So you’re tracking these parameters in your app, but how do you use the app to know if you need to use a barrier or if you can have unprotected sex with a very little chance of pregnancy? Flo, Kindara, and Clue all include a calendar tab that clearly, visually displays the days that you are menstruating, fertile, and ovulating. By pulling up the calendar, you can quickly see where you are in your cycle. If the app indicates that you are outside of your fertility window, then you may be able to have unprotected sex with a very low risk of becoming pregnant. If you want to have intercourse but your cycle app indicates you are highly fertile, to avoid pregnancy, abstinence or use of a barrier method will be necessary. This is the general strategy behind using cycle tracking apps in conjunction with barrier methods as natural birth control. Consider this too, that if you are having sex during the fertile window, your natural birth control will only be as effective as the barrier method you choose,⁵ so be sure to read through the options described in our next post.

Track 3 cycles before going skin-to-skin

But before considering forgoing barriers and diving straight into skin-to-skin intercourse during non-fertile periods, we strongly recommend committing to diligently tracking at least three menstrual cycles to truly get to know your body and give whichever app you’re using enough data to calculate accurate predictions for you. Be consistent during this time, doing your best to enter data into the app every day. Remember, the most important parameters to track are cervical fluid observations, basal body temperature, and LH levels. After a few months, you and the app are able to better understand what’s happening in your body even if your tracking becomes a little less consistent. With that information though, you can more accurately predict when you will be in your fertile window and know if you either need to abstain from sex or implement a barrier method on any given day.*

Using a cycle tracking app to predict your fertile window does rely on cycle regularity. If you have a very irregular cycle, then this is not a suitable solution for birth control. In that situation we strongly recommend working with a qualified health care provider who can help you get your cycle back on track.

Fertility Monitors

Both ClearBlue and Pearl map self-collected hormone data to a digital interface to determine the fertile window.

ClearBlue

ClearBlue can be purchased as either a fertility monitor (recommended) or a fertility stick. ClearBlue was developed to help women conceive but it accurately identifies the fertile window and so can be used as a tool to avoid pregnancy. Simply urinate on a test strip on certain days of the month and avoid unprotected intercourse around your fertile days.

Pearl

Pearl is a kit with 15 FSH (blue) tests, 15 LH (pink) tests, and 2 hCG (pregnancy) tests. Purchase of the kit gives you access to a cycle tracking app which analyzes photographs of the test strips and warns you 6 days in advance of your approaching fertile window. Simply urinate on a test strip, snap a photo on your smartphone and the app integrates this information to give you feedback on what your hormone levels are at that time and how fertile you are. It also tracks data from your samples over time. Because it includes FSH test strips, Pearl allows people with premature ovarian failure to monitor FSH levels without a blood draw. Working with a qualified healthcare provider Pearl can provide individuals with premature ovarian failure some assessment about their pregnancy risk and is very useful for planning pregnancy when you have premature ovarian failure.

LH Test Strips

We love these natural birth control monitors and think they are especially helpful for beginners to Natural Birth Control. While ClearBlue and Pearl are a little more expensive, LH test strips are easily accessible and affordable. Cycle tracking apps Flo and Kindara allow you to enter LH testing strip data as part of your cycle charting. In the same study mentioned earlier comparing various ovulation predicting methods, their results indicated that LH strip testing is just as accurate as ultrasonography for predicting ovulation.⁶

Natural Birth Control with Premature Ovarian Failure

Ann is a 26 year old female with premature ovarian failure. Her FSH has been elevated above 40.0 mIU/mL for more than 2 years. Even though her risk of pregnancy is very low, she and her husband are not ready for a child. In premature ovarian failure, FSH levels and usually LH levels are elevated while typically estrogen is very low. FSH must drop and estrogen must increase for ovulation to occur. When estrogen increases, so does the lubricative cervical fluid. Because of this, Ann uses cervical fluid as her primary indicator of fertility. If any type of slippery cervical fluid or wet spots on her underwear appear she uses an FSH test strip from the Pearl fertility kit. If the FSH strip shows two lines this means her FSH is above 25, and it is unlikely that she will release an egg within the next 5 days. Alternately, if she does not have lubricative cervical fluid, she is safe to proceed even without testing FSH although it is a good idea to check it monthly.

References:

Contraception. https://www.cdc.gov/reproductivehealth/contraception/index.htm. Published August 13, 2020. Accessed March 16, 2021.
WebMD – Better information. Better health. https://www.webmd.com/sex/birth-control/birth-control-pills. Updated December 2020. Accessed April 6, 2021.
Center for Drug Evaluation. Research. Information about the risk of blood clots in women taking drospirenone. Published 2019. Accessed April 20, 2021.
Zethraeus N, Dreber A, Ranehill E, et al. A first-choice combined oral contraceptive influences general well-being in healthy women: a double-blind, randomized, placebo-controlled trial. Fertil Steril. 2017;107(5):1238-1245.
Weschler T. Taking Charge of Your Fertility, 10th Anniversary Edition: The Definitive Guide to Natural Birth Control, Pregnancy Achievement, and Reproductive Health. Harper Collins; 2006.
Guida M, Tommaselli GA, Palomba S, et al. Efficacy of methods for determining ovulation in a natural family planning program. Fertil Steril. 1999;72(5):900-904.
Mansour D, Inki P, Gemzell-Danielsson K. Efficacy of contraceptive methods: A review of the literature. Eur J Contracept Reprod Health Care. 2010;15(1):4-16.
Frank-Herrmann P, Heil J, Gnoth C, et al. The effectiveness of a fertility awareness based method to avoid pregnancy in relation to a couple’s sexual behaviour during the fertile time: a prospective longitudinal study. Human Reproduction. 2007;22(5):1310-1319. doi:10.1093/humrep/dem003
Centers for Disease Control and Prevention: Effectiveness of family planning methods. http://www.cdc.gov/reproductivehealth/UnintendedPregnancy/PDF/Contraceptive_methods_508.pdf. Accessed April 6, 2021.
Bigelow JL, Dunson DB, Stanford JB, Ecochard R, Gnoth C, Colombo B. Mucus observations in the fertile window: a better predictor of conception than timing of intercourse. Hum Reprod. 2004;19(4):889-892.

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Fertility Tracking