Cervical Mucus & Daysy: Why Daysy Doesn’t Need It

Daysy doesn’t need cervical mucus because its algorithm calculates your fertile window from your basal body temperature and cycle history alone. This is how Daysy identifies non-fertile (green) days with 99.4% accuracy.¹ Cervical mucus is still a valuable body sign: it shows you when your estrogen is rising and helps you spot your most fertile days when you’re trying to conceive.

At a glance

Cervical mucus is an estrogen sign: before ovulation, it becomes more abundant, clearer, and stretchier.^2,3
Daysy calculates your fertile window without cervical mucus, from basal body temperature and cycle history alone.
Daysy identifies non-fertile (green) days with 99.4% accuracy (107,020 cycles).¹
Mucus observation is subjective and varies from cycle to cycle;⁴ Daysy measures basal body temperature objectively with 0.05 °C sensor precision.
When you’re trying to conceive, mucus is worth watching: on days with the most fertile-type mucus, the chance of conception is close to 30%.⁵

What is cervical mucus and what does it show?

Cervical mucus changes with your hormonal cycle and shows you when your estrogen rises before ovulation.

Cervical mucus is produced in the cervix and changes throughout your cycle. It’s an estrogen sign: as estrogen rises before ovulation, the amount increases noticeably and the mucus becomes more fluid, typically clear, stretchy, and slippery.^2,3 In this phase, sperm can move through it especially easily.²

Why does cervical mucus matter when you’re trying to conceive?

The more fertile your cervical mucus, the higher your chance of getting pregnant.

The chance of conception increases with mucus quality.⁶ In a study of 193 women, it was 29% on days with the most fertile-type mucus and 0.3% on days with no noticeable mucus.⁵ So if you’re trying to get pregnant, your mucus can show you, in addition to your red Daysy days, when your most fertile days are.

Why doesn’t Daysy need cervical mucus?

Daysy accurately calculates your fertile window from basal body temperature and cycle history; it doesn’t need subjective mucus observations to do so.

Daysy automatically applies the rules of natural family planning (NFP) to your temperature and period data and calculates your fertile window from them. Daysy doesn’t need cervical mucus for this, for two reasons:

Temperature is enough for an accurate calculation. In an analysis of 107,020 cycles from 5,328 users, the Daysy algorithm identified non-fertile (green) days from basal body temperature and cycle history alone, with 99.4% accuracy.¹ When in doubt, Daysy stays red or yellow.
Mucus is subjective; temperature isn’t. How you perceive and classify the amount and texture of your mucus is your personal judgment. It varies considerably from cycle to cycle in the same woman,⁴ and not every day gets an entry. Basal body temperature, on the other hand, is measured objectively by Daysy: every morning, with the same hardware, 0.05 °C sensor precision, and fixed evaluation logic.

That’s why Daysy works according to the calculo-thermal method: basal body temperature plus cycle history. You can log your cervical mucus in the DaysyDay app for your own evaluation. To learn how Daysy applies the individual NFP rules, visit our NFP rules page.

NFP rules

How does Daysy calculate your fertile window?

Daysy measures your basal body temperature every morning and shows your fertility status as a traffic light: green, red, or yellow.

Daysy is a fertility tracker by Valley Electronics that determines ovulation as well as the fertile and non-fertile days in your cycle, for trying to conceive or cycle observation. Valley Electronics has been developing cycle computers since 1986, and Daysy is made in Germany.

Daysy measures your basal body temperature, meaning your body temperature at complete rest, every morning before you get up, under your tongue, in about 60 seconds. Before ovulation, your basal body temperature is lower; afterwards, under the influence of progesterone, it rises by about 0.4 to 0.8 °F (0.2 to 0.45 °C) and stays elevated until your next period. From this rise and your period entries, the algorithm calculates your fertility status and shows it as a traffic light:

Green: non-fertile day
Red: fertile or possibly fertile day
Yellow: Daysy is still learning your cycle, or there isn’t enough data for a clear result

Do cervical mucus and the Daysy display match?

Yes: on days when Daysy shows red, users logged a fertile mucus type in over 90% of their entries.

In an internal analysis that has not been published in a scientific journal, we looked at about 25,300 anonymized cycles from the DaysyDay app (2019 to 2023) in which users had logged their cervical mucus. We analyzed the six days around ovulation, as determined by Daysy from basal body temperature: the four days before (OV -4 to OV -1), the day of ovulation (OV), and the day after (OV +1). Daysy shows red on all of these days.

This applies to all three fertile mucus types: sticky, creamy, and egg white. “Dry” accounted for less than 10% of entries on each of these days.

The most common type was “egg white,” the mucus quality associated with the highest fertility: its share rose from about 38% of entries four days before ovulation to about 59% on the day before.

This is in line with research: in a study with daily ultrasound monitoring, self-observed peak-type mucus captured the fertile window in 96% of cases.³ Daysy’s fertile days and your own mucus observations describe the same hormonal process from two different angles.

How does the symptothermal method use cervical mucus and basal body temperature?

The symptothermal method combines basal body temperature and cervical mucus; Daysy supports you on the temperature side.

The symptothermal method is a fertility awareness method in which you observe your basal body temperature and cervical mucus and evaluate them together using fixed rules (double check).^7,8 In German-speaking countries, Sensiplan is the best-known version of the method.⁷ You do the evaluation yourself, so it’s worth learning the rules thoroughly, for example in a course or with a certified fertility awareness instructor.

Mucus alone isn’t enough: feeling dry shortly before ovulation doesn’t rule out fertility. That’s why the method combines mucus and temperature.

You can use Daysy’s data as an aid for your own self-evaluation with the symptothermal method:

Basal body temperature: You can see the temperatures measured by Daysy as a curve in the DaysyDay app.
Temperature rise: The temperature rise calculated by Daysy indicates ovulation.
Period data: You can also use your logged period days.
Cervical mucus: You can log your mucus observations in the DaysyDay app.

Combining temperature and mucus according to the method’s rules is something you do yourself. Daysy supports you on the temperature side.

Who is this for?

Daysy and mucus observation complement each other, especially when you’re trying to conceive or simply want to understand your cycle better.

Women trying to conceive who want to know exactly when they ovulate and also want to observe their cervical mucus.
Women who use the symptothermal method and want to make daily temperature tracking and charting easier.
Anyone who wants to understand their cycle better without having to rely on subjective mucus observation.

Learn more about the Daysy algorithm on our fertility tracker method page and in our overview of Daysy’s accuracy.

fertility tracker method

Daysy’s accuracy

Frequently asked questions about cervical mucus and Daysy

The most important answers about cervical mucus and Daysy at a glance.

Why doesn’t Daysy need cervical mucus?

Because the Daysy algorithm calculates your fertile window from basal body temperature and cycle history alone. This is how Daysy identifies non-fertile (green) days with 99.4% accuracy (van de Roemer et al. 2021). Mucus observation is also subjective and varies from cycle to cycle.

What is cervical mucus important for?

Cervical mucus is an estrogen sign. Before ovulation, it becomes more abundant, clearer, and stretchier. When you’re trying to conceive, it helps you spot your most fertile days: on days with the most fertile-type mucus, the chance of conception is close to 30%.

Can I log my cervical mucus in the Daysy app?

Yes. You can log your mucus observations in the DaysyDay app for your own evaluation. They aren’t used to calculate your fertile and non-fertile days.

Can I use Daysy for the symptothermal method?

Yes, Daysy’s data can serve as an aid for your own self-evaluation. Daysy measures your basal body temperature and calculates the temperature rise. You observe and evaluate your cervical mucus yourself.

How accurate is Daysy?

In an analysis of 107,020 cycles from 5,328 users, Daysy identified non-fertile (green) days with 99.4% accuracy (van de Roemer et al. 2021).

Learn more about this topic

Causes and origins of bloody discharge. How to interpret bloody discharge and what bloody cervical mucus may indicate.

Bloody Cervical Mucus

Guide to Observing Cervical Mucus: What cervical mucus reveals about your fertility, and how to observe and interpret it effectively.

Observing Cervical Mucus

Your guide to interpreting basal temperature charts and recognizing patterns – from typical temperature curves to potential signs of health changes.

Understanding BBT Charts

Sources

1)

van de Roemer, N.; Haile, L.; Koch, M. The performance of a fertility tracking device. The European Journal of Contraception & Reproductive Health Care. 26(2), 111–118 (2021).

DOI: 10.1080/13625187.2021.1871599. Available at: www.tandfonline.com .

2)

Andersch-Björkman, Y.; Thomsson, K. A.; Holmén Larsson, J. M.; Ekerhovd, E.; Hansson, G. C. Large Scale Identification of Proteins, Mucins, and Their O-Glycosylation in the Endocervical Mucus during the Menstrual Cycle. Molecular & Cellular Proteomics. 6(4), 708–716 (2007).

DOI: 10.1074/mcp.M600439-MCP200. Available at: doi.org .

3)

Ecochard, R.; Duterque, O.; Leiva, R.; Bouchard, T.; Vigil, P. Self-identification of the clinical fertile window and the ovulation period. Fertility and Sterility. 103(5), 1319–1325.e3 (2015).

DOI: 10.1016/j.fertnstert.2015.01.031. Available at: doi.org .

4)

Najmabadi, S.; Schliep, K. C.; Simonsen, S. E.; Porucznik, C. A.; Egger, M. J.; Stanford, J. B. Cervical mucus patterns and the fertile window in women without known subfertility: a pooled analysis of three cohorts. Human Reproduction. 36(7), 1784–1795 (2021).

DOI: 10.1093/humrep/deab049. Available at: doi.org .

5)

Scarpa, B.; Dunson, D. B.; Colombo, B. Cervical mucus secretions on the day of intercourse: an accurate marker of highly fertile days. European Journal of Obstetrics & Gynecology and Reproductive Biology. 125(1), 72–78 (2006).

DOI: 10.1016/j.ejogrb.2005.07.024. Available at: doi.org .

6)

Bigelow, J. L.; Dunson, D. B.; Stanford, J. B.; Ecochard, R.; Gnoth, C.; Colombo, B. Mucus observations in the fertile window: a better predictor of conception than timing of intercourse. Human Reproduction. 19(4), 889–892 (2004).

DOI: 10.1093/humrep/deh173. Available at: doi.org .

7)

Malteser Arbeitsgruppe NFP (MW Malteser Werke gGmbH). Natürlich und sicher. Das Arbeitsheft: Natürliche Familienplanung mit Sensiplan. TRIAS Verlag, ISBN 978-3-432-11626-6. (2022).

8)

Frank-Herrmann, P.; Heil, J.; Gnoth, C.; Toledo, E.; Baur, S.; Pyper, C.; Jenetzky, E.; Strowitzki, T.; Freundl, G. 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. 22(5), 1310–1319 (2007).

DOI: 10.1093/humrep/dem003. Available at: doi.org .

Why Doesn’t Daysy Need Cervical Mucus?

At a glance

What is cervical mucus and what does it show?

Why does cervical mucus matter when you’re trying to conceive?

Why doesn’t Daysy need cervical mucus?

How does Daysy calculate your fertile window?

Do cervical mucus and the Daysy display match?

How does the symptothermal method use cervical mucus and basal body temperature?

Who is this for?

Frequently asked questions about cervical mucus and Daysy

Learn more about this topic

Sources

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