Cervical mucus based NFP methods (or CMMs) focus on one primary sign of a woman’s fertility—cervical mucus.

CMMs provide critical information about a man and a woman's combined fertility that creates their fertile window. To appreciate CMMs it is important to understand basic facts about human fertility. Here only a brief description relevant to CMMs is discussed. A more detailed description both of human fertility and cervical mucus methods can be found in An Introduction to NFP.


A woman is fertile for only twenty-four hours in each menstrual cycle. The eruption of a mature egg from a woman's ovary is called ovulation. Prior to this event, a woman's body slowly becomes fertile due to the increase of the reproductive hormone, estrogen. Besides maturing the egg, estrogen also signals the woman's cervical canal to produce a fluid, or "mucus," that is critical to the survival of sperm in her body. When cervical mucus is present in a woman's body, a man's sperm can live for up to six days. That is why NFP methods will teach the facts about the fertile window, which is the result of the husband and wife's combined fertility.

During the time of approaching fertility, the woman can feel and even observe her cervical mucus on the outside of her body. CMMs teach a woman how to understand her cervical mucus and chart it to identify her time of fertility. Considering that sperm can live up to six days with the presence of cervical mucus, married couples can then attempt a pregnancy by targeting their conjugal relations during the fertile window. Husband and wife who discern that they should not attempt a pregnancy, can sexually abstain according to the guidelines of their CMM.

Learn CMM

Please note that each CMM based method treats the teaching of the sensation, observation, and daily charting of cervical mucus differently. In order to decide which CMM is best for you, contact the NFP provider. To view the list of national NFP providers, see Learn NFP.


CMM NFP Providers

Select Articles

(See the NFP Bibliography for a list of foundational and current research.)

Please be advised that the content below represents the research of the authors. Links to external websites are provided solely for the user's convenience. Reference to these sites do not imply USCCB official endorsement.

Please be patient with us as we continue to develop this page. Send suggestions to nfp@usccb.org.


A Prospective Multicentre Study of the Ovulation Method of NFP, III: Characteristics of the Menstrual Cycle and the Fertile Phase
World Health Organization
This study is the first international investigation of the Ovulation Method by the World Health Organization. Researchers studied the characteristics of the menstrual cycles of 725 women. Women were instructed not to use hormones or other forms of contraception, but rather to use the Ovulation Method of NFP (self-recognition of cervical mucus) during the fertile phase. 

Approaching Menopause: The Ovulation Method
Evelyn L. Billings
This article highlights the symptoms leading up to, and during menopause. A woman's cycle may become irregular at this phase of life. Due to this time of life, Dr. Billings stresses the importance of cervical mucus self-regulation and following the guidelines of the Ovulation Method to determine the times of fertility.

Cervical Factors
Erik Odebald
Dr. Odebald describes experimental investigations done on cervical mucus. There are many different techniques as to how to conduct these studies but Odebald uses this article to discuss the most important results and their significance for fertility problems.

Continuous Mucus: Correlation of Point of Change with Preovulatory Rise in Estradiol-17 Beta
Lorna L. Cvetkovich, Thomas W. Hilgers, Barbara B. Gentrup
Cervical mucus observation may be difficult for women who experience continuous mucus throughout their menstrual cycles. This study aims to prove the value of cervical mucus methods for these women. Rather than examining a woman's onset of cervical mucus, this study evaluates the "Point of Change" in the mucus and its correlation to the woman's hormone levels.

Natural Family Planning: Yesterday, Today, Tomorrow
John J. Billings
Dr. Billings and his wife, Evelyn are the creators of the Billings Ovulation Method. In this article, Dr. John describes how he and his wife discovered and developed the Ovulation Method.

The Biophysical Properties of the Cervical-Vaginal Secretions: Part I, Part II, Part III
Erik Odebald et al.
This article describes the work of many researchers over the course of 27 years and the contributions of their work to Natural Family Planning. Dr. Odebald and his colleagues classify the different types of mucus during the phases of the menstrual cycle. This facilitates a sharper recognition of the signs of ovulation.

The Mucus Symptom's Length and Subphases during the Fertile Age
Erik Odebald
Along with his colleagues, Dr. Erik Odebald, chairman of the Department of Medical Biophysics at the University of Umea, Sweden, studied the length and quality of the mucus phases throughout a woman's menstrual cycle. Dr. Odebald and his team analyzed over one hundred records of menstrual cycles fulfilling certain criteria.Their results provide further insight into the woman's reproductive cycle and comprise a strong base for understanding several methods of Natural Family Planning.

The Two-Day Method
See our page, "Other Natural Methods" to learn about the simple cervical mucus method that asks two easy questions to identify the fertile window.


Back to NFP Science