Cervical Health Awareness Month
Cervical Mucus as a Marker of Fertility: A Review of Research
By: Mariah West, DO
Director’s Note: January is Cervical Health Awareness Month, and this week we feature a brief summary of research  that examined the accuracy of cervical mucus as a biomarker of fertility. The study titled, “Cervical mucus secretions on the day of intercourse: an accurate marker of highly fertile days” was reviewed by Dr. Mariah West, a family medicine resident and former FACTS elective participant. Modern fertility awareness-based methods (FABMs) provide women a range of biomarkers to track for family planning and to monitor their reproductive and overall health. The Billings Ovulation Method is one of the most thoroughly researched FABMs. In the study summarized below, Scarpa et al present a valuable statistical analysis of fertility based upon cervical mucus observations among couples charting with the Billings Ovulation Method.
Many natural methods have been developed over the last half century for women to identify their “fertile window,” which is defined as the 5 days before ovulation and ovulation itself. Natural family planning (NFP) or fertility awareness-based methods (FABMs) use a woman’s cervical mucus and other biomarkers to identify the fertile window and ovulation. These methods have long been used as a technique for women to achieve or avoid/delay pregnancy.
Cervical mucus is produced by the endocervical crypts in response to an increase in estrogen just before ovulation. Estrogen-induced mucus can be easily identified by women based on the observation and/or sensation of cervical discharge on the vulva. By observing and tracking cervical mucus, women are able to approximate the days in which they can be considered fertile. Fertile mucus, or type E mucus, is identified as thin, translucent, lubricative, and clear in color. One of the oldest and most studied methods to identify cervical mucus is the Billings Ovulation Method. This method was created for women to chart their monthly cycles to identify menses, dry, and wet days; wet days represent the presence of cervical mucus. Using this method, a woman can correctly identify her fertile window.
“Estrogen-induced mucus can be easily identified by women based on the observation and/or sensation of cervical discharge on the vulva. Fertile mucus, or type E mucus, is identified as thin, translucent, lubricative, and clear in color.”
This study was based in Italy. Researchers gained access to volunteers via four institutions teaching the Billings Ovulation Method between 1993 and 1997. There were 193 women willing to take part in this study. Entry criteria included experienced use of the Billings Method, married or in a stable relationship, 18-40 years of age, had at least one menses after cessation of breastfeeding or after delivery, and not taking hormonal medication or drugs affecting fertility. The participants were followed prospectively based upon their daily logging of menstrual bleeding and cervical mucus observations. Statistical analysis was used to identify the day of conception in couples who used the Billings Method to conceive. The researchers were also interested in identifying which mucus type and symptom is most sufficient for family planning. Data was collected daily with probability scores of conception based solely upon mucus observations reported by participants. Mucus was reported based on a numerical score from 1 to 4, with a score of 1 being dry and 4 being the most fertile type.
Fertile-type mucus was reported an average of 6 times per cycle. Intercourse was reported by couples an average of 4.15 times per cycle, with a standard deviation of 2.41. Couples in the study averaged intercourse 6% of the time with a mucus score of 4 and 19% of the time with a mucus score of 1 to 3. On days with no mucus score, the probability of conception was 0.003, which is essentially a zero percent chance. With a mucus score of 2, the probability of conception was 0.013, and 0.025 with a mucus score of 3. With a mucus score of 4, the most fertile-type mucus, the probability of conception increases dramatically to 0.29, which is statistically significant. This study was done with couples who were trying to achieve and avoid pregnancy, so the results do not reflect one pattern versus another.
“With a mucus score of 4, the most fertile-type mucus, the probability of conception increases dramatically to 0.29, which is statistically significant.”
Cervical mucus categorization is a valuable tool to avoid or achieve pregnancy. This study reinforces the importance of cervical mucus observation for women who want to monitor their fertility with natural methods. The simplicity of categorizing mucus in numerical order from 1 to 4 enables women to monitor their fertility easily and effectively. This study showed that on dry days, there is essentially a zero percent likelihood of conception, whereas the probability increases substantially when a woman notes fertile-type mucus (level 4), which occurs mid-cycle in most women.
“This study showed that on dry days, there is essentially a zero percent likelihood of conception, whereas the probability increases substantially when a woman notes fertile-type mucus (level 4).”
Limitations of this study include the reliance on mucus observations by individuals, as these are subjective recordings. However, each participant was well trained and educated in the use of the Billings Ovulation Method for cervical mucus observation. Although this study provides a good statistical analysis of fertility based upon mucus observations, it does not give any probabilities of pregnancy. Further research should be done comparing couples who wish to conceive versus couples that do not wish to conceive. Furthermore, it would be advantageous for future studies to have a method to quantify results using a device for precise measurement of cervical mucus characteristics, removing any subjectivity from the study.
 Scarpa B, Dunson DB, Colombo B. Cervical mucus secretions on the day of intercourse: an accurate marker of highly fertile days. Eur J Obstet Gynecol Reprod Biol. 2006 Mar 1;125(1):72-8. doi: 10.1016/j.ejogrb.2005.07.024. Epub 2005 Sep 8. PMID: 16154254.
ABOUT THE AUTHOR
Mariah West, DO
Mariah West, DO is an intern at OSU-OMECO Family Medicine Residency. She attended medical school at Oklahoma State University College of Osteopathic Medicine in Tulsa, OK, graduating in May 2023 with honors in family medicine. She completed her undergraduate education at East Central University in Ada, Oklahoma, where she received a B.S. in biology. Mariah is passionate about providing quality primary care to patients in rural Oklahoma. She enrolled in the FACTS elective to become more competent in women’s health and to gain a better understanding of natural family planning methods to be able to offer patients a natural method to monitor fertility.