Clinical and Experimental Obstetrics & Gynecology, 49(1), 2022
Fertile window and biophysical biomarkers of cervical secretion in subfertile cycles: a look at biotechnology applied to NaProTechnology
José María Murcia Lora, Óscar Martínez Martínez , Martínez Calvo M
Jennifer Simoni , Alberto Falces de Andrés , Mejia J, Simoni D , Jorge Enrique Mejía, Diglio A. Simoni, Juan Luis Alcázar, Alcázar J, Andrés A, Jennifer S, Marian Martínez Calvo
Author affiliations (6)
Unit of Restaurative Roproductive Medicine, Clinical Consulting G&E, 26002 Logroño, La Rioja, Spain
The principal objective of this study was to correlate biophysical properties of vaginal discharge present in the cervical mucus with the timing of the fertile window. In particular, we produce measures of the viscoelasticity of the cervical secretion using two methods. The first uses only the elasticity extracted from the Creighton Model Fertility Care System (CrMs) scale, calculated P-6 ovulation estimated day (OED) with respect to the peak day of the CrMs. The second uses a numerical method that takes into account the changes in viscoelasticity, but without reference to the peak day calculated using the CrMs model. Using both methods, twelve records were obtained from a single female subject.
Methods
The methodology used to evaluate the viscoelasticity factor was by measuring the approximate length in centimeters (cm) of the vaginal discharge of cervical discharge. For this, the scale of the stretching graph established by observing the stretching of CrMS was used, taking into account the previous 6 days at peak day P-6. The first method, which we termed CFW (Clinical Fertile Window), uses a measure based on the approximate length (cm) of the maximal stretchiness of the vaginal discharge. The second method we termed SFW (Software-CrMS/strectching) (Software-based Fertile Window).
Results
The fertile window was detected correctly in 100% of the cases using either method, and a correlation value of 0.71 was observed between the two methods.
Conclusions
We conclude that the assessment of viscoelasticity using SFW algorithm allowed in this pilot study to detect the fertile window and to describe the evolution pattern of cervical discharge throughout the fertile window. Our study provides support for the use of computational methods in detecting the fertile window, taking only into account the time evolution of the cervical discharge throughout the menstrual cycle.
DOI 10.31083/j.ceog4901017 10.31083/j.ceog4901017 Lora et al. 2022, Lora 2022
Cite this article
Murcia Lora, J. M., Martínez Martínez, O., Simoni, J., Martínez Calvo, M., de Andrés, A. F., Enrique Mejía, J., Simoni, D., & Alcázar, J. L. (2022). Fertile window and biophysical biomarkers of cervical secretion in subfertile cycles: a look at biotechnology applied to NaProTechnology. Clinical and Experimental Obstetrics & Gynecology, 49(1). https://doi.org/10.31083/j.ceog4901017
Murcia Lora JM, Martínez Martínez O, Simoni J, Martínez Calvo M, de Andrés AF, Enrique Mejía J, et al. Fertile window and biophysical biomarkers of cervical secretion in subfertile cycles: a look at biotechnology applied to NaProTechnology. Clin. Exp. Obstet. Gynecol.. 2022;49(1). doi:10.31083/j.ceog4901017
Murcia Lora, J. M., et al. "Fertile window and biophysical biomarkers of cervical secretion in subfertile cycles: a look at biotechnology applied to NaProTechnology." Clinical and Experimental Obstetrics & Gynecology, vol. 49, no. 1, 2022.
Stanford JB, 2004·The Medical and Surgical Practice of NaProTECHNOLOGY·
The Mucus Cycle Score, derived from the standardized CrMS daily observations, quantifies cervical mucus quality and quantity across a cycle and correlates with measured estrogen levels and fecundity rates, providing a non-invasive index of reproductive potential. Declining mucus scores are clinically actionable, directing investigation into hypoestrogenism, cervical pathology, or medication effects that reduce cycle fecundity and can be corrected before ART is considered.
The ovulation method provides a woman with an awareness of her cervical mucus pattern. This enables her to mark the beginning and end of the fertile phase of the cycle as well as the time of maximum fertility. Not only is the time of ovulation located but also there is recognition of infertility in the absence of ovulation. The key to understanding is the concept of the basic infertile pattern which precedes the commencement of follicular development; the key to successful use is competent teaching. After preliminary considerations on the fertile phase the determination of ovulation and the aspect of periodic abstinence two basic studies comparing clinical and hormonal observations are reviewed showing how accurately the cervical mucus reflects ovarian activity. Understanding the basic infertile pattern and the two sets of rules (the early day rules and peak rule identifying respectively the beginning and end of the fertile period) is basic to the application of the ovulation method. Criteria for the ideal family planning method and the importance of quality teaching are presented. Two problems requiring attention in NFP are restrictive terminology in data collection and a lack of fully developed and positive approach to periodic abstinence.
Accurate timing of ovulation is especially necessary (1) in artificial insemination in order to avoid wastage of donor semen; (2) in cases where the husband is relatively infertile and it is necessary to conserve his semen. While many physicians rely upon the basal body temperature curve for timing ovulation, the interpretation of such curves is varied. Some physicians believe ovulation occurs prior to the lowest point in the temperature cycle, while others believe that ovulation occurs either at the low point or following the thermal shift. We have been disappointed in our ability to interpret the basal body temperature curve for accurate timing of ovulation, and have placed greater reliance upon concurrent phenomena, such as changes in the quantity and viscosity of cervical mucus and the cyclic changes observed in the vaginal smear. Although the relationship between the occurrence of a profuse, thin cervical mucus discharge and the optimal time of fertility in the human has been recognized for the past century, in our opinion this relationship requires further evaluation.
In his excellent review, "Cervical mucus: Cyclic variations and their clinical significance," Shettles quotes Robin who, in 1848, noted the viscous nature of human cervical secretions; and Smith who, in 1865, concluded that conception is most likely when the mucus contents of the cervix are in the most fluid condition. J. Marion Sims, who invented a vaginal speculum and first described the postcoital examination in 1868, observed that the test is positive for motile spermatozoa when the cervical mucus becomes clear and translucent, and about the consistency of the white of egg. Although these observations on human cervical mucus have been well documented, they have been almost disregarded by gynecologists. The significance of the cyclical outpouring of cervical mucus has been rediscovered in the past few years and has aroused great interest in students of sterility.
The optimal time of fertility in domestic animals is the period of heat or estrus. In 1925, Woodman and Hammond showed that during estrus, bovine cervical mucus is fluid and capable of being drawn out into threads, whereas in diestrus the mucus is thick. Seguy and Vimeux, and Seguy and Simonnet called attention to the optimal conditions of longevity of human spermatozoa in the fluid, glairy mucus of the cervix at midcycle. They postulated that these changes in cervical mucus were associated with ovulation and could be compared to the period of estrus in subprimate mammals. They correlated these changes with visual evidence of ovulation at laparotomy. Subject: ively, many women observe an increased sticky, mucoid discharge which is typical at midcycle and which is present over a period of days. On occasion this discharge is blood-tinged and may be compared to the distinct bloody mucoid discharge present in the domestic animal "in heat."
This mucus can be seen exuding from the cervix at midcycle and it may be aspirated from the endocervix and actually weighed, as reported by Viergiver and Pommerenke. Clift demonstrated certain rheologic properties of cervical mucus, especially flow elasticity and Spinnbarkeit. Flow elasticity, or elastic recoil of mucus, is measured by an instrument described by Blair. The use of the Blair capillary viscometer is a cumbersome method which we discontinued. We have had no experience with the new modification of the viscometer described by Clift, Glover, and Blair. Spinnbarkeit is easily tested, and we have found it to be a very practical objective method for determining viscosity of cervical mucus. In performing this test (Fig. 1), a vaginal speculum is inserted, exposing the cervix. A glass cannula is inserted into the endocervix and by means of gentle suction, a quantity of endocervical mucus is obtained. This mucus is blown onto a glass slide and a cover slip is placed on it. The mucus adheres to both the slide and the cover slip, and by withdrawing the cover slip, a thread of mucus is formed which can be measured in centimeters (Fig. 2). Usually, the cover slip is withdrawn several times, and the average length of the thread is ascertained. It is our purpose to show the relationship of Spinnbarkeit to other cyclic phenomena occurring during the menstrual cycle, such as basal body temperatures, vaginal smears, quantity of cervical mucus, and longevity of spermatozoa (Fig. 3).
What is the normal range of cervical mucus patterns and number of days with high or moderate day-specific probability of pregnancy (if intercourse occurs on a specific day) based on cervical mucus secretion, in women without known subfertility, and how are these patterns related to parity and age? The mean days of peak type (estrogenic) mucus per cycle was 6.4, the mean number of potentially fertile days was 12.1; parous versus nulliparous, and younger nulliparous (<30 years) versus older nulliparous women had more days of peak type mucus, and more potentially fertile days in each cycle. The rise in estrogen prior to ovulation supports the secretion of increasing quantity and estrogenic quality of cervical mucus, and the subsequent rise in progesterone after ovulation causes an abrupt decrease in mucus secretion. Cervical mucus secretion on each day correlates highly with the probability of pregnancy if intercourse occurs on that day, and overall cervical mucus quality for the cycle correlates with cycle fecundability. No prior studies have described parity and age jointly in relation to cervical mucus patterns. STUDY DESIGN, SIZE, This study is a secondary data analysis, combining data from three cohorts of women: 'Creighton Model MultiCenter Fecundability Study' (CMFS: retrospective cohort, 1990-1996), 'Time to Pregnancy in Normal Fertility' (TTP: randomized trial, 2003-2006), and 'Creighton Model Effectiveness, Intentions, and Behaviors Assessment' (CEIBA: prospective cohort, 2009-2013). We evaluated cervical mucus patterns and estimated fertile window in 2488 ovulatory cycles of 528 women, followed for up to 1 year. PARTICIPANTS/MATERIALS, SETTING, Participants were US or Canadian women age 18-40 years, not pregnant, and without any known subfertility. Women were trained to use a standardized protocol (the Creighton Model) for daily vulvar observation, description, and recording of cervical mucus. The mucus peak day (the last day of estrogenic quality mucus) was used as the estimated day of ovulation. We conducted dichotomous stratified analyses for cervical mucus patterns by age, parity, race, recent oral contraceptive use (within 60 days), partial breast feeding, alcohol, and smoking. Focusing on the clinical characteristics most correlated to cervical mucus patterns, linear mixed models were used to assess continuous cervical mucus parameters and generalized linear models using Poisson regression with robust variance were used to assess dichotomous outcomes, stratifying by women's parity and age, while adjusting for recent oral contraceptive use and breast feeding. MAIN The majority of women were <30 years of age (75.4%) (median 27; IQR 24-29), non-Hispanic white (88.1%), with high socioeconomic indicators, and nulliparous (70.8%). The mean (SD) days of estrogenic (peak type) mucus per cycle (a conservative indicator of the fertile window) was 6.4 (4.2) days (median 6; IQR 4-8). The mean (SD) number of any potentially fertile days (a broader clinical indicator of the fertile window) was 12.1 (5.4) days (median 11; IQR 9-14). Taking into account recent oral contraceptive use and breastfeeding, nulliparous women age ≥30 years compared to nulliparous women age <30 years had fewer mean days of peak type mucus per cycle (5.3 versus 6.4 days, P = 0.02), and fewer potentially fertile days (11.8 versus 13.9 days, P < 0.01). Compared to nulliparous women age <30 years, the likelihood of cycles with peak type mucus ≤2 days, potentially fertile days ≤9, and cervical mucus cycle score (for estrogenic quality of mucus) ≤5.0 were significantly higher among nulliparous women age ≥30 years, 1.90 (95% confidence interval (CI) 1.18, 3.06); 1.46 (95% CI 1.12, 1.91); and 1.45 (95% CI 1.03, 2.05), respectively. Between parous women, there was little difference in mucus parameters by age. Thresholds set a priori for within-woman variability of cervical mucus parameters by cycle were examined as follows: most minus fewest days of peak type mucus >3 days (exceeded by 72% of women), most minus fewest days of non-peak type mucus >4 days (exceeded by 54% of women), greatest minus least cervical mucus cycle score >4.0 (exceeded by 73% of women), and most minus fewest potentially fertile days >8 days (found in 50% of women). Race did not have any association with cervical mucus parameters. Recent oral contraceptive use was associated with reduced cervical mucus cycle score and partial breast feeding was associated with a higher number of days of mucus (both peak type and non-peak type), consistent with prior research. Among the women for whom data were available (CEIBA and TTP), alcohol and tobacco use had minimal impact on cervical mucus parameters. LIMITATIONS, We did not have data on some factors that may impact ovulation, hormone levels, and mucus secretion, such as physical activity and body mass index. We cannot exclude the possibility that some women had unknown subfertility or undiagnosed gynecologic disorders. Only 27 women were age 35 or older. Our study participants were geographically dispersed but relatively homogeneous with regard to race, ethnicity, income, and educational level, which may limit the generalizability of the findings. Patterns of cervical mucus secretion observed by women are an indicator of fecundity and the fertile window that are consistent with the known associations of age and parity with fecundity. The number of potentially fertile days (12 days) is likely greater than commonly assumed, while the number of days of highly estrogenic mucus (and higher probability of pregnancy) correlates with prior identifications of the fertile window (6 days). There may be substantial variability in fecundability between cycles for the same woman. Future work can use cervical mucus secretion as an indicator of fecundity and should investigate the distribution of similar cycle parameters in women with various reproductive or gynecologic pathologies. STUDY FUNDING/COMPETING INTEREST(S): Funding for the three cohorts analyzed was provided by the Robert Wood Johnson Foundation (CMFS), the Eunice Kennedy Shriver National Institute of Child Health and Human Development (TTP), and the Office of Family Planning, Office of Population Affairs, Health and Human Services (CEIBA). The authors declare that they have no conflict of interest. N/A.