April 8, 2021

FACTS Infertility Awareness Series

FABM Applications in Subfertility: A Research Review


By Jenna Karrow



Editor’s Note: This outstanding article opens our April series to raise awareness about infertility and the many aspects of health and wellbeing affected by this condition. Jenna Karrow wrote it while on the online FACTS fertility awareness elective now attended by 192 students since the fall of 2020. She summarized the research article titled, “‘Fertility Awareness-Based Methods’ and subfertility: a systematic review” published by Thijssen et al in 2014.

Beyond her informative summary of a systematic review about FABMs and subfertility, this month we will publish research reviews about infertility and its impact on endometriosis and on mental health. We will also publish an interview with an Ob-Gyn physician who shares ways he uses FABMs in daily practice as powerful tools to enhance the care of women and couples. Our series will end with a beautiful story of a mother and her adult daughter, and how FABMs brought healing to each of them and ignited their passion to impact entire communities through education. You don’t want to miss it! 

An Introduction to FABMs

The possibility of subfertility is almost certain in 50% of couples when pregnancy is not achieved after six cycles of unprotected intercourse (Gnoth et al, 2003; Wang et al, 2003; Sozou and Hartshorne, 2012). For these couples, assisted reproductive technologies (ART) can be pursued to achieve pregnancy. However, there is great utility and potential for these couples to use fertility awareness-based methods (FABMs) to increase the chance of conception. FABMs can be used to achieve or avoid pregnancy by a woman monitoring physical symptoms, such as cervical mucus and basal body temperature (BBT). Since these symptoms are a result of hormone fluctuations, they can be used to identify fertile and infertile days of a woman’s cycle. Rather than counseling couples to have frequent intercourse—such as every other day—to achieve pregnancy, FABMs provide a targeted, direct strategy to increase pregnancy rates (ASRM, 2008).

Cervical mucus monitoring (CMM) is a reliable and cost-effective type of FABM. With the rise of estrogen prior to ovulation, cervical mucus changes to become more conducive to fertility. During this fertile window, which includes the day of ovulation and the five days prior, cervical mucus can increase in volume and become more “clear, wet, stretchy, and slippery” (Hilgers and Prebil, 1979). This change in consistency of cervical mucus is beneficial for transport, survival, and functional maturation of spermatozoa. During the luteal phase, after ovulation, cervical mucus becomes more “dry, sticky, cloudy, and not stretchy” (Pallone and Bergus, 2009; Stanford et al, 2002). The rise in progesterone is responsible for this change in cervical mucus that impedes sperm maturation and movement (Pallone and Bergus, 2009; Stanford et al, 2002).

A cervical mucus score can be estimated from 1 to 4. A low mucus score of 1 corresponds to drier discharge that is less fertile, whereas a high mucus score of 4 corresponds with fertile stretchy, slippery mucus (Colombo and Masarotto, 2000; Dunson et al, 2001; Bigelow et al, 2004). These changes in cervical mucus are detectable by women and can be used to identify their fertile window.

In addition to its drying effect on cervical mucus, increased progesterone leads to a rise in basal body temperature by 0.3-0.6°C. Daily temperature monitoring can detect an increase in temperature that remains steady, and this change corresponds to the end of the fertile window in each cycle (Pallone and Bergus, 2009).

Specific types of FABMs include the Billings Ovulation Method, the Creighton Model, the TwoDay Method, and the Sympto-Thermal Method. With the Billings Ovulation Method, a woman tracks her cervical mucus and describes it in her own words (Bhargava et al, 1996; Stanford et al, 1999). The Creighton Model utilizes standardized words for categorizing cervical mucus (Howard and Stanford, 1999; Pallone and Bergus, 2009). The TwoDay Method evaluates the presence or absence of cervical mucus; if there is cervical mucus present one day, then fertility is assumed on that day and the next day (Jennings et al, 2011). The Sympto-Thermal Method involves cervical mucus monitoring, BBT tracking, and calculation rules (Frank-Herrmann et al, 2007; Pallone and Bergus, 2009). This method has been shown to be highly effective given the “double check mechanism” (Frank-Herrmann et al, 2007).


The 2014 article by Thijssen et al summarized here utilized a MEDLINE search to evaluate the impact of cervical mucus monitoring on pregnancy rates, particularly in couples with subfertility. Search terms included: fertility awareness, self-assessment, cervical mucus, infertility, subfertility, natural family planning, conception, Sympto-Thermal Method, Billings Ovulation Method, and Creighton Model, in combination with ‘not contraception.’ Studies were excluded if they focused on pregnancy prevention and fertility awareness-based methods for contraception, cancer, and breastfeeding. The search was narrowed down from 3,331 articles to 10 articles to be included in the review. 

Brief Summary of Results of Ten Articles Reviewed

  • In the Colombo et al (2000) study, women tracked cervical mucus, BBT, and intercourse. The study showed that the two days before peak mucus day (day -2) had the greatest likelihood (0.203) of achieving pregnancy when looking at intercourse patterns. Colombo et al (2006) determined that peak mucus day (day 0) correlated with the greatest probability of conception at 0.429.
  • Dunson et al (2001) used the TwoDay Method and reported that fertile days, as determined by the presence of cervical mucus, had the greatest chance of pregnancy. There was a 50% increased rate of pregnancy if mucus was observed for two consecutive days, and they estimated peak day as two days prior to ovulation.
  • Stanford et al (2003) compared pregnancy rates among fertile and subfertile couples using the Creighton Model in four different cities. They found that the peak mucus day, also considered ovulation, had the greatest chance of conception. For fertile couples, the probability of conception on peak mucus day was 0.38 and for subfertile couples, it was 0.14.
  • Bigelow et al (2004) noted an increased likelihood of pregnancy with higher cervical mucus scores rather than the timing of intercourse. Their results concluded that 5 days prior to ovulation constitutes the lowest fertility, but 3 days prior to ovulation is the highest fertility, when using only BBT.
  • Frank-Herrmann et al (2005) showed that although women can distinguish ovulation well with CMM and BBT, using both measures was a better predictor. Additionally, pregnancy was achieved by 81% after 6 months and 92% after 12 months when using fertility-focused intercourse based on FABMs.
  • Scarpa et al (2006) studied the impact of cervical mucus scores on the probability of conception. They found that on days with no cervical mucus, conception was improbable, with a likelihood of conception rising to nearly 30% on days with fertile-type mucus.
  • Scarpa et al (2007) demonstrated that timing intercourse during days with the highest mucus score, which only occurred between cycle days 7 and 20, can shorten the time to pregnancy. Conversely, days outside this time frame had a very low likelihood of conception.
  • Evans-Hocker et al (2013) investigated women using CMM to categorize their cervical mucus and its usefulness in achieving pregnancy. They found that with consistent use of CMM, fecundability increases and the time to pregnancy can be decreased for couples.
  • Mu et al (2014) reported an increase in pregnancy rates of 0.87 when intercourse occurred on high or peak days, but a rate of 0.5 correlated with intercourse during low mucus days. Women used CMM and/or electronic hormonal fertility monitoring.


These ten studies have demonstrated the utility of FABMs to increase the likelihood of achieving pregnancy by using cervical mucus monitoring to identify the fertile window. When using BBT, the greatest likelihood of pregnancy occurs one to two days prior to ovulation. By purposefully timing intercourse during high mucus score days during the mid-cycle, couples can achieve pregnancy more quickly. FABMs can also be used to help diagnose couples with subfertility and as an alternative to assisted reproductive technologies.



ASRM. Optimizing natural fertility. Fertil Steril. 2008;90:S1–6.

Bigelow JL, Dunson DB, Stanford JB, et al. Mucus observations in the fertile window: a better predictor of conception than timing of intercourse. Hum Reprod. 2004;19:889-892.

Colombo B, Masarotto G. Daily fecundability: first results from a new data base. Demogr Res. 2000;3:39.

Colombo B, Mion A, Passarin K, et al. Cervical mucus symptom and daily fecundability: first results from a new database. Stat Methods Med Res. 2006;15:161–180.

Dunson DB, Sinai I, Colombo B. The relationship between ­cervical secretions and the daily probabilities of pregnancy: effectiveness of the TwoDay Algorithm. Hum Reprod. 2001;16:2278–2282.

Evans-Hoeker E, Pritchard DA, Long DL, et al. Cervical mucus monitoring prevalence and associated fecundability in women trying to conceive. Fertil Steril. 2013;100:1033–1038.

Frank-Herrmann P, Gnoth C, Baur S, et al. Determination of the fertile window: reproductive competence of women – ­European cycle databases. Gynecol Endocrinol. 2005;20:305–312.

Frank-Herrmann P, Heil J, Gnoth C, et al. 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. Hum Reprod. 2007;22:1310–1319.

Gnoth C, Godehardt D, Godehardt E, et al. Time to pregnancy: results of the German prospective study and impact on the management of infertility. Hum Reprod. 2003;18:1959–1966

Hilgers TW, Prebil AM. The ovulation method – vulvar ­observations as an index of fertility/infertility. Obstet ­Gynecol. 1979;53:12–22.

Jennings V, Sinai I, Sacieta L, et al. TwoDay Method: a quick-start approach. Contraception. 2011;84:144–149.

Mu Q, Fehring RJ. MCN Am J Matern Child Nurs. 2014;39:35–40.

Pallone SR, Bergus GR. Fertility awareness-based methods: another option for family planning. 2009;22:147–157.

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;125:72–78.

Scarpa B, Dunson DB, Giacchi E. Bayesian selection of ­optimal rules for timing intercourse to conceive by using calendar and mucus. Fertil Steril. 2007;88:915–924.

Stanford JB, Smith KR, Dunson DB. Vulvar mucus observations and the probability of pregnancy. Obstet Gynecol. 2003;101:1285–1293. 

Thijssen, A., Meier, A., Panis, K., & Ombelet, W. (2014). ‘Fertility Awareness-Based Methods’ and subfertility: a systematic review. Facts, views & vision in ObGyn6(3), 113–123.

Wang X, Chen C, Wang L, et al. Conception, early pregnancy loss, and time to clinical pregnancy: a population-based prospective study. Fertil Steril. 2003;79:577–784.

About the Author

Jenna Karrow

Author Bio: Jenna Karrow is a fourth-year medical student at Des Moines University in Des Moines, Iowa. She plans to pursue residency in obstetrics and gynecology. She is grateful to have a background in FABMs in order to educate future patients.



The FACTS 2021 CME Conference

Fertility Awareness – Expanding Care for Women’s Health

On the heels of the success of our fall 2020 two-day CME virtual conference, we are excited to announce the details for our 2021 event. We are looking forward to this year’s virtual conference as an opportunity to connect with one another, to learn more about fertility awareness, and to explore timely topics in women’s reproductive health together. Expand your toolbox and join us in May!  Click here for more details and registration information.We hope to “see” you there!

• FABM overview and their applications for:
– Hypothalamic Amenorrhea
– Dysmenorrhea
– Thyroid Dysfunction
– Infertility
– Recurrent Pregnancy Loss
– Adolescence and Body Literacy
– Polycystic Ovarian Syndrome (PCOS)

• Fem Tech – NeoFertility and FEMM
• Functional Medicine in Women’s Health and FABMs
• Extensive Q&A with our expert panels
• Bonus Pre-conference Presentations!
• CME Credit*
*AAFP (American Academy of Family Physicians) CME credit is pending.

Can’t make it on these days?! Not to worry – Your registration will also allow access to these presentations through the end of 2021!

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