Fehring, R. J., Raviele, K., & Schneider, M. (2004). A comparison of the fertile phase as determined by the Clearplan Easy Fertility Monitor and self-assessment of cervical mucus. Contraception, 69(1), 9-14. https://doi.org/10.1016/j.contraception.2003.09.011
Fehring RJ, Raviele K, Schneider M. A comparison of the fertile phase as determined by the Clearplan Easy Fertility Monitor and self-assessment of cervical mucus. Contraception. 2004;69(1):9-14. doi:10.1016/j.contraception.2003.09.011
Fehring, R. J., et al. "A comparison of the fertile phase as determined by the Clearplan Easy Fertility Monitor and self-assessment of cervical mucus." Contraception, vol. 69, no. 1, 2004, pp. 9-14.
Fertility monitor and cervical mucus find nearly the same peak day
The fertility monitor and cervical mucus picked nearly the same peak fertility day. In a 2004 study of 100 women charting 378 cycles, the Clearplan Easy Fertility Monitor averaged day 16.5 and mucus day 16.3. On average, mucus marked the start of the fertile window earlier.
Key Findings
One hundred women observed cervical mucus and used the monitor daily for 2 to 6 cycles, producing 378 cycles of data. Of these, 92% had a monitor peak.
Mean first peak day: 16.5 (SD = 3.6) by the monitor, 16.3 (SD = 3.7) by cervical mucus. Peak days by the two methods correlated at r = 0.85 (p < 0.001).
Mean start of the fertile window: day 11.8 (SD = 3.4) by the monitor, day 9.9 (SD = 3.0) by mucus. Correlation was r = 0.43 (p < 0.001).
Cervical mucus gave a fertile phase averaging 10.9 days (SD = 3.7), longer than the monitor's fertile phase (p < 0.001).
The authors conclude that the monitor tends to underestimate the fertile phase and that self-assessed mucus tends to overestimate it.
Interpretation
This observational study compared two markers in 100 healthy women aged 18 to 42, recruited from a university clinic and a private practice. Every woman was learning to monitor her fertility. The results compare the timing of the two markers within the same cycles. The study defined the estimated day of ovulation from the monitor's second peak day and reports no ultrasound or pregnancy outcomes. Women rated their own mucus. Agreement on the start of the fertile window was moderate.
RRM Context
Cervical mucus observation is a core marker in Creighton, Billings and Marquette-style charting. This study came from Marquette University's Institute for Natural Family Planning. The close match on peak day fits the charting principle that the body's own signs mark the ovulatory event. Sperm survive in mucus, so the fertile window concerns both partners.
Our editorial summary of this paper, not the article's abstract.
Abstract
The purpose of this study was to compare the fertile phase of the menstrual cycle as determined by the Clearplan Easy Fertility Monitor (CPEFM) with self-monitoring of cervical mucus. One-hundred women (mean age = 29.4 years) observed their cervical mucus and monitored their urine for estrogen and luteinizing hormone metabolites with the CPEFM on a daily basis for 2-6 cycles and generated 378 cycles of data; of these, 347 (92%) had a CPEFM peak. The beginning of the fertile window was, on average, day 11.8 (SD = 3.4) by the monitor and day 9.9 (SD = 3.0) by cervical mucus (r = 0.43, p < 0.001). The average first day of peak fertility by the monitor was 16.5 (SD = 3.6) and by cervical mucus 16.3 (SD = 3.7) (r = 0.85, p < 0.001). The mean length of the fertile phase by the monitor was 7.7 days (SD = 3.1) and by cervical mucus 10.9 days (SD = 3.7) (t = 12.7, p < 0.001). The peak in fertility as determined by the monitor and by self-assessment of cervical mucus is similar but the monitor tends to underestimate and self-assessment of cervical mucus tends to overestimate the actual fertile phase.
Bouchard TP et al., 2026·Journal of ovarian research·Free to read
Reproductive hormones of the fertile window are often referenced to women in regular cycles, but this may not be representative of the hormonal profiles of women in different circumstances like polycystic ovarian syndrome, the postpartum period, and the perimenopause transition. This observational cohort study sought to identify the variability in the reproductive hormones in various clinical circumstances and to establish potential thresholds for each category based on hormone measurements with the Mira urinary hormone monitor. A total of 57 women (ages 22-51) in various circumstances (regular cycles, polycystic ovarian syndrome, postpartum and perimenopause) tracked Mira urine hormone measurements (estrone-3-glucuronide, luteinizing hormone, pregnanediol glucuronide), contributing 444 cycles of data. Using additive mixed models, hormone values were stratified by the four different reproductive categories. The perimenopause and polycystic ovarian syndrome groups demonstrated relative hypoestrogenic states, while the perimenopause group showed low luteal pregnanediol glucuronide and the polycystic ovarian syndrome/polyendocrine metabolic ovarian syndrome (PCOS/PMOS) group showed high luteal pregnanediol glucuronide. The perimenopause group had significantly higher luteinizing hormone values throughout the whole cycle. The fertile window hormone thresholds vary depending on a woman's specific reproductive category. Women in different circumstances should not necessarily use the same hormonal thresholds for the fertile window and ovulation. A larger dataset with ultrasound correlation to ovulation is required to delineate the fertile window with more precision. Hormone differences across the menstrual cycle could be used for targeted treatments in polycystic ovarian syndrome and perimenopause women.
Malliou-Becher MN et al., 2026·Human reproduction (Oxford, England)
What are the variations in ovulation time and menstrual cycle characteristics among and within various individuals over the course of 12 menstrual cycles? There are considerable variations in both cycle length and ovulation time, with pronounced intra-individual variability over a 12-cycle observation period. Although it is commonly believed that healthy women have regular cycles with a predictable mid-cycle ovulation, more recent research shows a significant variation in cycle length and ovulation time. Previous studies have focused only on cycle length, often excluding cycles outside the 25-35-day range, thus limiting the understanding of natural variation; they have also lacked precise ovulation diagnostics or included small sample sizes, making it difficult to capture the full scope of cycle and ovulation variability. Similarly, a recent big data study, while valuable, was limited by a self-selected group and the absence of accurate ovulation diagnostics, reducing its generalizability. STUDY DESIGN, SIZE, This study was designed as a prospective long-term observational study, which involved collecting data from 1923 women with a total of 43 999 menstrual cycles from January 1985 to July 2019. After fulfilling the inclusion criteria, the main group consisted of 1051 women, all of whom contributed data for 12 cycles (12 612 cycles), including 420 conception cycles. PARTICIPANTS/MATERIALS, SETTING, Participants in the study were between 18 and 44 years of age at study entry and did not take any reproductive hormones. Women who were postpartum, breastfeeding, amenorrheic, or within a 3-month period after stopping hormonal contraception were excluded. Participants agreed to keep cycle records according to the symptothermal method, 'Sensiplan'. Ovulation time was determined using an evidence-based algorithm based on evaluating cervical mucus patterns and basal body temperature shifts, with ovulation time defined as the day before the temperature rise. Data analysis was descriptive, using absolute and relative frequencies, standard deviation, percentiles, and ranges. Age dependency was assessed using unpaired sample t-tests and one-way ANOVA. Linear regression was used to assess long-term trends. MAIN In 62.4% of women, cycle lengths varied by 1 week or more within 12 cycles. Accordingly, the time of ovulation varied by 1 week or more within 12 cycles in 54.8% of women, with 96.5% experiencing fluctuations of 4 days or more over the 12 months. The median spontaneous cycle length was 28 days, with a mean of 29.66 days (SD = 7.55). Only 52.7% of women consistently had cycle lengths between 23 and 35 days across all 12 cycles. Ovulation occurred most frequently between Days 12 and 16, with almost half of conceptions (45.7%) occurring after Day 16. A one-way analysis of variance revealed a significant reduction in mean cycle length with increasing age (P < 0.001), showing the shortest median cycle length of 27 days being in women aged 40-44 years. Age also impacted ovulation time, with women aged 35-39 years showing more stable ovulation patterns compared to younger women. Over the 34-year study period, average cycle length increased slightly but significantly (β = 0.0161, P = 0.0306), corresponding to approximately half a day. Intra-individual variability also showed a slight, but non-significant, upward trend (β = 0.0262, P = 0.2173). LIMITATIONS, Comorbidities such as hyperprolactinemia, obesity, and PCOS were not systematically excluded. However, by including only women with at least 12 cycles, the study largely avoided severe hormonal disorders. This study highlights the considerable individual variation of ovulation time and cycle length over 12 menstrual cycles. These findings contribute to a better understanding of fertility awareness, and highlight the implications for family planning and reproductive health management. STUDY FUNDING/COMPETING INTEREST(S): The authors declare no conflicts of interest. No funding was provided. N/A.
Bouchard TP et al., 2025·Preprints.org·Free to read
Background/Objectives: Quantitative urine monitors are increasingly being used for a personalized approach to improve menstrual cycle knowledge and to manage fertility. Although several studies have evaluated urine fertility monitors in regular cycles, there is limited research in the use of quantitative monitors in reproductive disorders, such as polycystic ovarian syndrome (PCOS). Urine hormone data was collected with the Mira monitor from 20 participants, 10 of whom had PCOS and a matched group who had regular cycles. The main aim of this study was to evaluate the levels of luteinizing hormone (LH), estrone-3-glucuronide (E13G), and pregnanediol glucuronide (PDG) in PCOS menstrual cycles compared to regular cycles. Women with PCOS had higher BMI than regular cycling women (p=0.02). PCOS cycles were longer (p<0.05), peak day was later in the menstrual cycle (p<0.001), and luteal length was shorter (p < 0.01) compared to regular cycles. In whole cycle comparisons, E13G was found to be lower in PCOS cycles (p<0.01) and PDG was found to be higher in PCOS cycles (p<0.05). E13G was also lower in the follicular phase of and late luteal phase of PCOS cycles (p<0.00001). The results of this study demonstrate the feasibility of detecting hormonal differences in PCOS compared to regular cycles with at-home measurements with the Mira monitor. The metabolic dysregulation of PCOS is a possible factor in these hormone changes. Larger studies with different sub-types of PCOS will be needed to further clarify these changes and to understand the pathophysiology behind these hormonal changes.
Fehring RJ et al., 2007·J Obstet Gynecol Neonatal Nurs·Free to read
To determine the effectiveness of an electronic hormonal fertility monitor plus cervical mucus monitoring to avoid pregnancy.
A 12-month prospective clinical efficacy trial. One hundred ninety five (195) women (mean age 29.8 years) seeking to avoid pregnancy with a natural method at 5 clinical sites in 4 cities. Each participant was taught to track fertility by self-observation of cervical mucus and an electronic monitor that measures urinary levels of estrone-3-glucuronide and luteinizing hormone. Correctand typical-use unintended pregnancy rates. There were a total of 26 unintended pregnancies, 3 with correct use. With 1,795 months of use, the correct-use pregnancy rate was 2.1% per 12 months of use (i.e., 97.9% effective in avoiding pregnancy when rules of the method were always followed) and the imperfect-use pregnancy rate was 14.2% per 12 months of use (i.e., 85.8% effective in avoiding pregnancy when rules of the method were not always followed and all unintended pregnancies and months of use were included in the calculations). Correct use of an electronic hormonal fertility monitor with cervical mucus observations can be as effective as other fertility awareness-based methods of natural family planning. Comparative studies are needed to confirm this conclusion.
Ecochard R et al., 1984·Contraception, fertilite, sexualite
24 women, of whom 2 each presented with primary and secondary infertility, were taught to observe their cervical mucus secretions outside the vulva. The correlation between the sensation, presence, and aspect of the mucus and the quantity of estrone and estradiol excreted in the urine were determined for each day of the cycle. The women were aged 24-39 years and had 0-7 children, with an average of 2.3. 2 women kept incomplete records and 2 had anovulatory cycles, leaving 20 in the sample. All 20 noted at least 1 day of fertile type mucus. 11 women noted 3 or fewer days which corresponded to the estrogenic peak. 4 of the women who noted more than 3 days of fertile type mucus identified 1-3 days of maximum wetness, bringing to 15 the number of favorable cases. In 4 cases the women observed fertile type mucus outside the estrogenic peak. In 14 cases the fertile type mucus was preceded by 1 or more days of thick mucus. It is hoped that this method will be of use in the treatment of infertility.
Evans-Hoeker E et al., 2013·Fertil Steril·Free full text on PubMed Central
To assess the use of cervical mucus monitoring (CMM) in women trying to conceive and determine whether monitoring is associated with increased cycle-specific probability of conception (fecundability). Time-to-pregnancy cohort study. Population-based cohort. PATIENT(S): Three hundred thirty-one women trying to conceive, ages 30 to 44 years, without known infertility. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): CMM prevalence and fecundability. RESULT(S): During the first cycle of the study, CMM was performed consistently (checked on >66% of pertinent cycle days) by 20 women (6%), inconsistently (34% to 66% of days) by 60 women (18%), infrequently (≤33% of days) by 73 women (22%), and not performed by 178 women (54%). Cycles in which CMM was consistently performed were statistically significantly more likely to result in conception after adjusting for age, race, previous pregnancy, body mass index, intercourse frequency, and urinary luteinizing hormone (LH) monitoring. Fecundability also increased with increasing consistency of CMM. CONCLUSION(S): Among women trying to conceive, CMM is uncommon, but our study suggests that CMM-a free, self-directed method to determine the fertile window-is associated with increased fecundability independent of intercourse frequency or use of urinary LH monitoring.
The (PD) peak day of cervical mucus is an important biologic marker for the self-determination of the optimal time of fertility in a woman's menstrual cycle. The purpose of this article is to provide evidence (literature and empiric) for the accuracy of the PD of cervical mucus as a biologic marker of peak fertility and the estimated day of ovulation. An analysis of data from four published studies that compared the self-determination of the PD of cervical mucus with the urinary luteinizing hormone (LH) surge was conducted. The four studies yielded 108 menstrual cycle charts from 53 women participants. The 108 cycles ranged in length from 22 to 75 days (mean 29.4 SD 6.0). Ninety-three of the 108 cycles had both an identified PD and LH surge. Data charts showed that 97.8% of the PD fell within +/-4 days of the estimated day of ovulation. Use of a standardized mucus cycle scoring system indicated that the peak in cervical mucus ratings was highest on the day of the LH surge. Self-determination of the PD of cervical mucus is a very accurate means of determining peak fertility and a fairly accurate means of determining the day of ovulation and the beginning of the end of the fertile time.
Fertility Awareness › Methods › Billings Ovulation Method · Menstrual Cycle › Cycle Biomarkers › Cervical Mucus · Research Methods › Measurement and Statistics › Instrument Development and Validation
Richard J Fehring, Mary Schneider, Kathleen Raviele
Rick Fehring, Dick Fehring, Rich Fehring, R Fehring, M Schneider, K Raviele
PMID 14720613 14720613 DOI 10.1016/j.contraception.2003.09.011 10.1016/j.contraception.2003.09.011 Fehring et al. 2004, Fehring 2004
Cite this article
Fehring, R. J., Raviele, K., & Schneider, M. (2004). A comparison of the fertile phase as determined by the Clearplan Easy Fertility Monitor and self-assessment of cervical mucus. Contraception, 69(1), 9-14. https://doi.org/10.1016/j.contraception.2003.09.011
Fehring RJ, Raviele K, Schneider M. A comparison of the fertile phase as determined by the Clearplan Easy Fertility Monitor and self-assessment of cervical mucus. Contraception. 2004;69(1):9-14. doi:10.1016/j.contraception.2003.09.011
Fehring, R. J., et al. "A comparison of the fertile phase as determined by the Clearplan Easy Fertility Monitor and self-assessment of cervical mucus." Contraception, vol. 69, no. 1, 2004, pp. 9-14.
04gr4te78