Who’s Best at Identifying Peak Day: Women, Experts or an Algorithm?

By: Brigitte Bonner

Director’s Note: Over the years, research in women’s health has seen myriad methods, devices, and algorithms designed to help women and couples more easily identify their window of fertility. Researchers have studied the merits of cervical mucus observations, basal body temperature, and urinary hormone measurements to track ovulation. Yet, with so many options available, the question remains, who is best at identifying the “peak day” associated with the fertile window? In the study[1] summarized below by Brigitte Bonner, a former FACTS elective student, Stanford et al sought to answer this question. Their research compared the accuracy of women identifying their own peak day to expert assessments and to an algorithm designed to do the same. Published in 2020, the article is titled, “Comparison of women-picked, expert-picked, and computer-picked Peak Day of cervical mucus with blinded urine luteinizing hormone surge for concurrent identification of ovulation.”

Introduction

For pregnancy to occur, many events must transpire within very specific time frames. In women with regular menstrual cycles, ovulation happens once per cycle, and the ovum can only be fertilized within the first 12-24 hours of its release from the ovary.[2] For couples trying to grow their family, the ability to identify this fertile window can be essential to reduce the time needed to conceive.

The physiologic process leading to ovulation involves many hormones, including follicle-stimulating hormone (FSH), estradiol, luteinizing hormone (LH), and progesterone. The drastic surge in LH levels occurring in most cycles about one day prior to ovulation can be measured via serum or urine LH levels.[1] Other biomarkers that signal ovulation include cervical mucus quality, basal body temperature, and calculations using menstrual cycle length. Natural or fertility awareness-based methods (FABMs) of family planning are tools to achieve or delay pregnancy by using these biomarkers to help people identify their fertile window. Benefits for FABM users include low cost, lack of side effects, patient autonomy, and the opportunity to gain a greater understanding of their bodies.[3]

The Creighton Model FertilityCare™ System (CrM) is an FABM that relies on observations of cervical mucus throughout a woman’s cycle using a standardized protocol to identify the “Peak Day,” which correlates closely with ovulation. Ninety-five percent of the the time the Peak Day occurs within ±3 days of ovulation.[1] According to the CrM, the Peak Day is the last day in the menstrual cycle when cervical mucus can be identified by the woman as either clear, stretchy, or lubricative. The CrM has all the benefits of FABMs and can be used in the setting of regular cycles, long cycles, recent discontinuation of oral contraceptives, and breastfeeding.[4]

“Benefits for FABM users include low cost, lack of side effects, patient autonomy, and the opportunity to gain a greater understanding of their bodies.”

Methodology

The study[1] by Stanford et al sought to ascertain how accurately patients newly taught the CrM could identify their Peak Day compared to (1) experts trained in the CrM and (2) computer algorithms designed to identify the Peak Day according to the CrM guidelines. This research is a secondary analysis of a randomized trial of women using the CrM when attempting to conceive. All Peak Days identified by women, experts, and the computer algorithm were compared to an objective day of ovulation. This was defined as one day after an LH surge detected by daily urinary LH values collected by a blinded form of the ClearBlue® Easy Fertility Monitor. The goal of this investigation was to determine how well women without prior experience with the CrM could identify their Peak Day to predict ovulation.[1]

Results

Stanford et al’s analysis showed the ‘women-picked’ Peak Days were most accurately correlated with the objective ovulation date, with 84% within ±2 days and 92% within ±4 days. ‘Expert-picked’ and ‘computer-picked’ Peak Day accuracy was lower than women-picked — 76% and 71%, respectively, within ±2 days — and 90% and 87% within ±4 days. Whereas experts and the computer algorithm identified Peak Days in nearly every cycle, women identified Peak Days in 63% of cycles recorded.

The researchers also analyzed how the accuracy changed in women-picked Peak Days over time. The data showed no statistical significance in the accuracy from the first cycle observed throughout the rest of the cycles. This further supports that women new to the CrM can use this method accurately, since they can effectively identify their Peak Day beginning with the first cycle they chart.

“Women new to the CrM can use this method accurately, since they can effectively identify their Peak Day beginning with the first cycle they chart.”

A computer algorithm was also used to identify the “Best Quality Day,” which was defined as the day having the most qualities describing fertile-type cervical mucus: clear, stretchy, and lubricative. In contrast, the CrM defines the Peak Day as the last day with any of the qualities of fertile-type cervical mucus. The Best Quality Day was the least accurate of the tested approaches, resulting in Peak Day correlating to actual ovulation day 58% of the time within ±2 days and 74% within ±4 days. This reinforces the CrM-defined Peak Day as the last day of any fertile-type mucus to be the best predictor of ovulation.

Discussion

Women and couples use FABMs for many different reasons. Whether chosen for environmental or financial reasons, religious beliefs, to become more aware of their body, or based on a negative prior experience with other forms of family planning, FABMs can be used by women in all circumstances. These methods are accurate and empower women to feel in control of their bodies.

“FABMs enable women to take note of the physiologic changes during their cycles and use that information to determine their fertility status on any given day. This study showed that women-picked Peak Days can be even more precise compared to experts or algorithms.”

The menstrual cycle is a key marker of a person’s overall health and can be affected by stress, pregnancy, breastfeeding, and lifestyle habits.[5] FABMs enable women to take note of the physiologic changes during their cycles and use that information to determine their fertility status on any given day. This study by Stanford et al showed that women-picked Peak Days can be even more precise compared to experts or algorithms. While women-picked Peak Days were more accurate, they were only identifying the most obvious Peak Days compared to experts and algorithms, who identified all of them.[1]Using observations about cervical mucus is an effective, low-cost, and low-risk method to identify a woman’s fertile window.

References

[1] J. B. Stanford, K. C. Schliep, C.-P. Chang, J.-P. O’Sullivan and C. A. Porucznik, “Comparison of women-picked, expert-picked, and computer-picked Peak Day of cervical mucus with blinded urine luteinising hormone surge for concurrent identification of ovulation,” Paediatric and perinatal epidemiology, vol. 34, no. 2, pp. 105-113, March 2020.
[2] Duane M, Stanford JB, Porucznik CA and Vigil P (2022) Fertility Awareness-Based Methods for Women’s Health and Family Planning. Front Med9:858977. doi: 10.3389/fmed.2022.858977.
[3] J. B. Stanford and C. A. Porucznik, “Enrollment, Childbearing Motivations, and Intentions of Couples in the Creighton Model Effectiveness, Intentions, and Behaviors Assessment (CEIBA) Study,” Frontiers in medicine, vol. 4, p. 147, 8 September 2017.
[4] M. P. Howard and J. B. Stanford, “Pregnancy Probabilities During Use of the Creighton Model Fertility Care System,” Archives of Family Medicine, vol. 8, pp. 391-402, 1999.
[5] R. Fehring and M. Schneider, “Variability in the Phases of the Menstrual Cycle,” Journal of Obstetric, Gynecologic, & Neonatal Nursing, vol. 35, no. 3, pp. 376-384, 2006.

ABOUT THE AUTHOR

Brigitte Bonner

Brigitte Bonner is a fourth-year medical student at Burrell College of Osteopathic Medicine in Las Cruces, NM. She received a bachelor of science in biology from Pepperdine University in Malibu, CA. She is passionate about educating and caring for underserved populations. She enrolled in the FACTS elective to be equipped to offer alternative methods of reproductive healthcare to patients from all backgrounds and life situations. She values the ability to provide options to patients so they have autonomy to choose whichever method of care they prefer.