An Introduction to Natural Family Planning

A note to our visitors ...

The text below provides basic information about Catholic teaching on marriage, conjugal love and responsible parenthood, the science and methods of Natural Family Planning, and married couple's experience in living the NFP life-style. This text can be purchased as a booklet from the Natural Family Planning Program, USCCB, orders: 1-866-582-0943; @email. Publication numbers: English language, #9921; Spanish language, #9927.

You have permission to reproduce the text only in part. Please cite as follows: Text taken from, Theresa Notare, Ed. Introduction to Natural Family Planning (Washington, DC: USCCB, 2009). Excerpts reprinted with permission.




A Special Message to You About Married Love and the Gift of Life

This is a small volume about the methods of Natural Family Planning (NFP). In a world of unbelievably amazing technology, this little book will introduce you to the novel idea that something valuable can be gained through something that is simply, well, natural. You will learn the basics of human fertility and gain an understanding of the methods of NFP. If you are married, or planning to marry, hopefully this introduction will inspire you to learn one of the methods of NFP by contacting an organization listed under Resources. Learning an NFP method is an important step to strengthen a marriage. Why? Because the methods of NFP respect God’s plan for marriage!

Marriage is a gift from God. Whether an individual marries or not, everyone benefits from marriage. Marriage nurtures the individual, creates the family and ties the rest of society together. God’s incredible design for marriage is discovered in Sacred Scripture. God created man and woman to embody His life and love: “God created man in His image; in the divine image He created him; male and female He created them” (Gn. 1:27). God desired spouses to share in His procreative love, in reality, to be co-creators with Him, bringing new life into the world: “Be fertile and multiply; fill the earth and subdue it” (Gn. 1:28). God planned that in marriage the mystery of human sexuality would be revealed as man and woman are brought together in a special union—two distinct parts of a whole humanity each with distinct gifts of fertility. Husband and wife are called to be reflections of God’s love to the world.

In their physical complementarity, spouses can say, as did Adam and Eve: “This one, at last, is bone of my bones and flesh of my flesh” (Gn. 2:23). The oneness shared by a husband and wife forms an intimate partnership of life and love: “That is why a man leaves his father and mother and clings to his wife, and the two of them become one body” (Gn. 2:24). In this way, marriage is distinct from all other human relationships. In their mutual self-surrender of giving and receiving love, they form a Communion of Persons. In their mutual love for each other, husband and wife reflect God’s own inner Trinitarian communion of love and life. In fact, they actually participate in God’s way of loving. The power of this intimate marital sharing of love enables spouses, with God’s grace, to create a home that welcomes children.

Sometimes, it is easy to forget that the physical expression of love between spouses (the marital embrace) has a divine twofold purpose. Sexual intercourse unites husband and wife physically and is also meant to draw them into an ever-deeper oneness of mind and heart. At the same time, the marital embrace is designed by God as the means for bringing new life into the world. It is a real participation in God’s love—love that gives and receives and creates life. Love and life are pure gifts from God. Spouses are meant to share in God's creative spirit through their openness to children. This is why the married couple's fertility, which enables them to bring into the world children made in God's own image, is a priceless gift that should never be rejected or harmed. Let’s take a closer look at this reality through hearing from the U.S. Catholic bishops in their document Married Love and the Gift of Life:1

What does the Church teach about married love?

Marriage is more than a civil contract; it is a lifelong covenant of love between a man and a woman. It is an intimate partnership in which husbands and wives learn to give and receive love unselfishly, and then teach their children to do so as well. Christian marriage in particular is a “great mystery,” a sign of the love between Christ and his Church (Eph. 5:32).

Married love is powerfully embodied in the spouses’ sexual relationship, when they most fully express what it means to become “one body” (Gn. 2:24) or “one flesh” (Mk. 10:8, Mt. 19:6). The Church teaches that the sexual union of husband and wife is meant to express the full meaning of love, its power to bind a couple together and its openness to new life.

What does this have to do with contraception?

A husband and wife express their committed love not only with words, but with the language of their bodies.

Married love differs from any other love in the world. By its nature, the love of husband and wife is so complete, so ordered to a lifetime of communion with God and each other, that it is open to creating a new human being they will love and care for together. Part of God’s gift to husband and wife is this ability in and through their love to cooperate with God’s creative power. Therefore, the mutual gift of fertility is an integral part of the bonding power of marital intercourse. That power to create a new life with God is at the heart of what spouses share with each other.

Suppressing fertility by using contraception denies part of the inherent meaning of married sexuality and does harm to the couple’s unity. The total giving of oneself, body and soul, to one’s beloved is no time to say: “I give you everything I am—except...” The Church’s teaching is not only about observing a rule, but about preserving that total, mutual gift of two persons in its integrity.

Are couples expected to leave their family size entirely to chance?

Certainly not! The Church teaches that a couple may generously decide to have a large family or may for serious reasons choose not to have more children for the time being or even for an indefinite period (Humanae Vitae, no. 10).

What should a couple do if they have a good reason to avoid having a child?

A married couple can engage in marital intimacy during the natu­rally infertile times in a woman’s cycle, or after child-bearing years, without violating the meaning of marital intercourse in any way.

This is the principle behind natural family planning (NFP). Natural methods of family planning involve fertility education that enables couples to cooperate with the body as God designed it.

Is there really a difference between using contraception and practicing natural family planning?

On the surface, there may seem to be little difference. But the end result is not the only thing that matters, and the way we get to that result may make an enormous moral difference. Some ways respect God’s gifts to us while others do not. Couples who have practiced natural family planning after using contraception have experienced a profound difference in the meaning of their sexual intimacy.

When couples use contraception, either physical or chemical, they suppress their fertility, asserting that they alone have ultimate control over this power to create a new human life. With NFP, spouses respect God’s design for life and love. They may choose to refrain from sexual union during the woman’s fertile time, doing nothing to destroy the love-giving or life-giving meaning that is present. This is the difference between choosing to falsify the full marital language of the body and choosing at certain times not to speak that language.

The bishops conclude Married Love and the Gift of Life by reminding us that:

By using contraception, couples may think that they are avoiding problems or easing tensions, that they are exerting control over their lives. But the gift of being able to help create another person, a new human being with his or her own life, involves profound relationships. It affects our relationship with God, who created us complete with this powerful gift. It involves whether spouses will truly love and accept each other as they are, including their gift of fertility. Finally, it involves the way spouses will spontaneously accept their child as a gift from God and the fruit of their mutual love. Like all important relationships with other persons, it is not subject solely to our individual control. In the end, this gift is far richer and more rewarding than that.

Striving to understand God’s design for married love is difficult in today’s world where so many noisy messages compete for our attention. Taking the time to learn, reflect, and pray can help us hear God’s call. Remembering to listen for God’s voice in the teaching of the Church is essential. After all, and as the U.S. bishops wrote in the conclusion of Married Love and the Gift of Life, Church teaching “is an invitation for men and women—an invitation to let God be God, to receive the gift of God’s love and care, and to let this gift inform and transform us, so we may share that love with each other and with the world.”

Theresa Notare, PhD, Editor


1 U.S. Catholic Bishops, Married Love and the Gift of Life (Washington, DC: U.S. Conference of Catholic Bishops, 2006), provides a summary of Catholic teaching on marriage and the subject of the responsible transmission of human life. The complete text is available here: Married Love and the Gift of Life. Orders: USCCB Publishing, 1-800-235-8722; publication No. 5-787.

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What is NFP?

Natural Family Planning (NFP) is a general term for certain methods that are based on the observation of the naturally occurring signs and symptoms of the fertile and infertile phases of a woman's menstrual cycle. NFP methods are used to both achieve as well as avoid pregnancy.

Although the first methods of NFP were developed in the mid-twentieth century,2 natural approaches to determining the time of a woman’s periodic fertility are actually a very old practice. The ancient Greeks, for example, had their own theory of a woman’s ovulation that was based on their knowledge of fertility in animals. With the discovery of the woman’s time of ovulation in the early nineteenth century, scientists created a formula for a Safe Time that could help married couples plan their families. Fast forward to the 1930s when the Rhythm or Calendar Method was developed based on the research of two different scientists in two separate parts of the world who had studied hundreds of menstrual cycles. All of these natural methods did not account for the changing signs of fertility in a woman's menstrual cycle. 

Today, the methods of NFP take account of a woman’s changing signs of fertility. Based on observable signs and symptoms of the fertile and infertile phases of the woman’s menstrual cycle, NFP methods track the changes associated with ovulation and treat each menstrual cycle as unique. The accuracy of a woman’s observations about her fertility has been validated by scientific research.3

NFP represents a holistic approach to family planning. Both husband and wife are instructed to understand their combined fertility and to identify their family planning intention (whether to attempt to have a baby or not). The successful use of NFP to postpone or avoid pregnancy relies upon a couple following what they know about the method and matching their intimate behavior to their family planning intentions (whether they are attempting to achieve or postpone a pregnancy). Successful use of NFP requires a couple to communicate. In the daily charting of their fertile signs, married couples quickly appreciate their shared responsibility for family planning. Husbands are encouraged to “tune into” their wives’ cycles, and both spouses are encouraged to speak openly to each other about their sexual desires and their ideas on family size. 

Married couples using NFP to postpone or avoid pregnancy abstain from intercourse and genital contact when the woman is fertile and can conceive. The total days of abstinence will vary from woman to woman and even from cycle to cycle. This is an important point to remember—there will be differences in the length of abstinence. Whatever the length of the fertile phase, no barriers or chemicals are used at any time to avoid pregnancy. To achieve pregnancy couples have intercourse during the fertile time of the cycle. 

NFP is not a contraceptive, it does nothing to suppress or block conception. Instead, couples adjust their behavior according to their family planning intention (that is, whether they hope to achieve or avoid a pregnancy) using the naturally occurring signs and symptoms of a woman's menstrual cycle.

The methods of NFP represent authentic family planning because they respect the nature of sexual intercourse as God made it – to be love-giving and life-giving. NFP methods promote respect between husband and wife, openness to human life and recognize the value of children. When practiced well, NFP methods can help to enrich the bond between husband and wife. As holistic family planning that works with nature, the methods of NFP are acceptable for people of various religious and philosophical beliefs.


2 The Sympto-Thermal methods were developed in the late 1940s-early 1950s. Cervical mucus-based methods were developed in the mid-1960s-early 1970s.

3 See “Research in Natural Family Planning: A Review of Studies from 1998-2003,” in Current Medical Research, 14 (Summer/Fall 2003). See also the foundational NFP studies listed in, Richard Fehring, and Robert Kambic, Natural Family Planning Bibliography (Washington, DC, 1995), available online here: NFP Science Bibliography.

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Human Reproduction and the Signs of Fertility

To appreciate and understand NFP, some background in human reproductive anatomy and physiology is helpful. Let’s start at the beginning. The male cell of reproduction is the sperm and the female cell of reproduction is the egg (or ovum). The uniting of these two cells is called conception (or fertilization). It is the beginning of a human life. 

For pregnancy to occur, a number of conditions must be present to help the sperm and egg unite. The male sperm is produced in the testicles. During intercourse millions of sperm are released into the woman’s vagina. To survive, sperm need to be in a good environment. The woman’s vagina, which is mostly acidic, is actually a poor environment for sperm survival. At certain times in a woman’s menstrual cycle however, she produces a fluid called cervical mucus that will change the chemical nature of the vagina. Cervical mucus is necessary for sperm survival. Sperm can live in cervical mucus from 3 to 5 days. If no cervical mucus is present, sperm die within minutes.

Men produce sperm continuously throughout their lives. Women, on the other hand, are born with all the eggs they will ever have. During a woman’s menstrual cycle, one or more of her eggs will develop and mature. Ovulation is the event when an egg (or eggs) fully matures and leaves the ovary. Usually only one egg is released during a woman’s cycle. Sometimes a second egg is released within the same twenty-four hours. The mature egg (or eggs) once released, will generally live for about twelve to twenty-four hours. Thus, for a woman to become pregnant, three factors are very important: healthy sperm; healthy egg; and cervical mucus for sperm survival.

There are three phases of a woman’s menstrual cycle: the pre-ovulation phase (also called the follicular phase, the time when the egg, or eggs, develop in the ovary's follicle); the fertile phase (leading up to and including ovulation which is the time the egg is released by the ovary); and the post-ovulation phase (also called the luteal phase, the time after the egg is released). 

Pre-Ovulation (Follicular Phase)

The first phase of a woman’s cycle begins on the first day of her period (menstruation) and ends on the day of ovulation. This phase can vary in length and also includes the fertile window or fertile phase of the menstrual cycle. The fertile phase includes the day of ovulation and the five preceding days. The pre-ovulatory phase is also called the follicular phase of the menstrual cycle since the ovary's follicles which contain developing eggs, grow and ripen or mature until ovulation. 

A woman has thousands of eggs which are housed in two small organs called ovaries, one on each side of her body. The ovaries are near the fallopian tubes (see Figure 1). It is in the fallopian tubes where, if present, sperm will meet egg, fertilization will occur, and new human life will begin. 

In the first part of the menstrual cycle, a chemical messenger (hormone) from the brain signals one or more of the thousands of eggs in a woman’s body to develop. As the egg matures its follicle gives off another important hormone called estrogen. Estrogen is essential for fertility, because it helps to prepare both the inside of the vagina for sperm and the uterus for pregnancy. Most people know that the inside of the uterus must be built up with nutrient-rich endometrium cells to sustain a pregnancy; however, few people know the unique responsibility of the base of the uterus (cervix). The cervix is lined with mucus-producing cells that are stimulated by estrogen (see Figure 1). When produced, cervical mucus will neutralize the acidic nature of the vagina allowing the sperm to survive and move up through the uterus and into the fallopian tubes.

The length of pre-ovulation can change from cycle to cycle in the same woman. For example, a woman might ovulate (release an egg) on day 13 in one cycle and in the next cycle ovulate on day 10. Many reasons account for variations during this time, including post-hormonal contraception, breastfeeding, and perimenopause. Research also reveals that factors such as weight loss, emotional stress (good or bad), illness, and even diet can affect the time of ovulation. Despite this, the time of fertility can be known by a woman because her body produces signs that help her identify when her fertility begins, when it peaks, and when her fertility ends.

The Fertile Phase (Fertile Window)

The fertile phase, or fertile window of the menstrual cycle is part of the follicular phase. The fertile phase begins when there is an estrogen rise from a developing follicle. Research shows that the fertile phase lasts six days and includes the day of ovulation and the five preceding days. The reason that this phase is six days is because sperm can live for five days in a good environment that is produced by cervical mucus. The two most fertile days of this phase are the two days before ovulation.

Ovulation occurs when another hormone called luteinizing hormone or LH signals the ovary to release a mature egg. At this time the cervix itself changes from a closed, firm opening (os) that sits low in the pelvic cavity to a soft open os that is positioned higher in the pelvic cavity. Furthermore, the cervical opening produces clear slippery mucus which changes the acidic environment of the vagina and, in turn, will nourish and protect sperm that have been deposited during intercourse.

The time of the six-day fertile window can vary from cycle to cycle. Women can track this variation by monitoring her cervical mucus changes and/or by using hormonal fertility monitors that measure the rise in estrogen and the LH surge.

Post-Ovulation (Luteal Phase)

The third phase of the woman’s menstrual cycle begins after ovulation and ends the day before her next period. This is called the luteal phase; it is a time of infertility. The luteal phase is relatively stable in length (averaging about 10-16 days).

After ovulation has occurred, the woman’s body releases another hormone called progesterone. Progesterone has a number of important functions. It elevates the woman’s body temperature about 4 - 8 tenths of a degree Fahrenheit and can be detected by taking daily waking temperatures. This is called the basal body temperature (BBT). Progesterone also prepares the lining of the uterus for possible implantation of a new life. When the woman’s egg has been fertilized by the sperm, the embryo travels down the fallopian tube in a journey that takes six to nine days and imbeds in the wall of the mother’s uterus. The uterus will keep the new human being safe and nourished for the next nine months. Progesterone will also stimulate cervical cells to produce a thick mucus that closes off the opening of the cervix and becomes a barrier to sperm and bacteria. If, on the other hand, fertilization does not occur, levels of progesterone will decrease, the mucus plug will dissolve, and the lining of the uterus will shed. This shedding of the lining of the uterus, experienced by the woman as bleeding, is called menstruation (menses).


The text above is authored by Richard Fehring, PhD, RN

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Cervical Mucus Methods

A single-index method of NFP, cervical mucus-based methods (or CMMs), chart one primary sign of a woman’s fertility (cervical mucus). CMMs originated with the work of several researchers, notably the Drs. John and Evelyn Billings (Australia).

Due to the extensive work of the Billings, the “Billings Ovulation Method” (or “Ovulation Method”) became synonymous with CMMs. Today,
the BOM continues to be the most popular CMM world-wide. Other approaches to CMMs exist such as the Creighton Model FertilityCare Method, developed by Dr. Thomas Hilgers (USA).

The careful observation and charting of the presence of the woman’s cervical mucus on a day to day basis will ensure a couple’s success in achieving their family planning intention (to achieve, postpone, or avoid pregnancy). When practiced consistently, this observation will soon become part of a woman’s normal daily routine.

Keywords: Cervical Mucus, Peak Day, Daily Observation

*For further information on the Billings Ovulation Method see, Evelyn Billings and Ann Westmore, The Billings Method, Using the body’s natural signal of fertility to achieve or avoid pregnancy (2004). For CMM providers, see Resources.


Cervical mucus methods (CMMs), provide information about the changes in one sign of a woman’s fertility, that of cervical mucus. There are several variations of cervical mucus methods, each with different methods of observing and charting cervical mucus observations and with instructions as to when to abstain from intercourse when postponing or avoiding pregnancy. The following gives a general understanding of cervical mucus methods.

When an egg in a woman’s body starts to mature, the hormone estrogen increases and stimulates the cells lining the cervical canal to produce mucus. Once estrogen stimulates these cells, cervical mucus will be felt by the woman. The result of this hormonal activity is generally described by women as a feeling or sensation of wetness. Mucus can also be observed by wiping the vulvar area from front to back with toilet tissue each time the woman goes to the bathroom. When mucus is present on the tissue, it can be picked up and observed.

The woman must be consistent in daily sensing or observing the presence (or absence) of her cervical mucus. During fertility, as the estrogen level rises, cervical mucus changes in consistency and quantity. The sensation also changes to one of slipperiness and greater lubrication, which the woman can notice as she goes about her normal daily routine. The last day of clear, slippery, and abundant (egg white type) mucus or a slippery sensation of lubrication, followed by a definite change is called Peak Day. Ovulation occurs within 24 to 48 hours of the Peak Day. 

After ovulation, estrogen levels start to drop off, progesterone levels increase, and the cervical mucus becomes sticky and cloudy again and/or dry (see Figure 2). The woman will experience a sensation of dryness. Once ovulation occurs the egg lives 12-24 hours. The fertile phase is from the beginning of the changing mucus pattern until three full days past the Peak.

Achieving Pregnancy

If a couple wishes to achieve pregnancy, obviously the best time to have intercourse is when the woman is fertile. The optimal time to achieve pregnancy (using cervical mucus as a sign) is the day(s) of the greatest quantity and quality of cervical mucus. Good quality mucus is stretchy, clear and gives the woman a sensation of lubrication.

Avoiding Pregnancy

Menstruation is a potentially fertile time since a woman can ovulate early in any cycle. If postponing or avoiding pregnancy is desirable, it is recommended that a couple abstain from intercourse during menses. In addition, because a woman will need to be alert for the onset of mucus during the pre-ovulatory phase of the cycle, the evening of every other dry day (that is, a day where no mucus was present and no sensation of wetness or slipperiness was felt by the woman) can be used for intercourse. Alternate nights are used to ensure that any seminal fluid from the previous night’s intercourse has not masked the onset of cervical mucus. Other cervical mucus only methods have different instructions for intercourse during menses and for managing seminal fluids so that every other day intercourse is not necessary.

Once cervical mucus has been observed, intercourse and all genital to genital contact must be avoided every day while mucus is present. During this time, the last day of mucus (Peak) will have to be identified. Peak Day is identified as the last day of the most fertile sign, whether it is the last day of slippery, stretchy or blood tinged mucus or the last day of a lubricative, wet sensation. Peak cannot be reliably identified until the following day, when mucus undergoes a change under the influence of progesterone.

Cervical mucus methods identify the post-ovulatory phase of the cycle as beginning three full days after the Peak of cervical mucus. This time of infertility will last up to the first day of menstruation. During this phase of the cycle, intercourse can occur any time of the day or night.


The text above is authored by Richard Fehring, PhD, RN

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Sympto-Thermal Methods

A multi‑indexed method of NFP, Sympto-Thermal Methods (STM)* chart the primary signs of fertility (cervical mucus, basal body temperature, and cervical changes) as well as the secondary signs of fertility (breast tenderness, back pain, etc.).

STM is based on the work of various scientists, including Bonomi, the Billings, Döering, Keefe, Prem, Röetzer, and Völlman. Among STM providers, variations exist in some rules, charting two or more of the primary signs of fertility, as well as differences in chart symbols. Despite the variations, all refer to the multi-indexed method as “STM.”

The careful observation and charting of the several signs of fertility on a day to day basis by couples will ensure success in achieving their family planning intention (to achieve, postpone, or avoid pregnancy). When practiced consistently, this observation will soon become part of a woman’s normal daily routine.

Keywords: Cervical Mucus, BBT, Daily Observation

*For further information on one approach to the STM, see: John Kippley, The Art of Natural Family Planning. (Cincinnati, OH: Couple to Couple League, 1996).


For STM providers, see Resources.Sympto-Thermal Methods (STM) provide information on the primary signs of fertility: cervical mucus, basal body temperature, and cervical changes. STM education also provides information on secondary signs of fertility: breast tenderness, mid-cycle back pain, etc. Variations in STM rules, charting two or more of the primary signs of fertility, as well as differences in chart symbols, exist among NFP providers.

The beginning of the cervical mucus symptom is the beginning of the potentially fertile phase. In the pre-ovulatory phase, the increase in estrogen levels affect cervical mucus. As estrogen increases the cervical crypts are stimulated to produce mucus that is thin, clear, and lubricative. A woman will feel wet when estrogen levels increase. As cervical mucus gradually changes it will become clear in appearance and sometimes even blood tinged; stretchy when picked up and held between two fingers; and will have the sensation of slipperiness, lubrication, and/or wetness. The last day of this type of mucus followed by a definite change is Peak Day. Ovulation will occur on or around Peak, after which the mucus changes back to a thicker and sticky texture (see Figure 2).

The basal body temperature (BBT) is the waking temperature of a woman’s body after she has had at least six hours of sleep. The role of the BBT in this method is to support and confirm the mucus sign and identify that ovulation has taken place. The BBT is taken at approximately the same time each day under the same conditions. During the pre-ovulatory phase, it remains at a low level. It is only after ovulation has taken place that a significant rise in the temperature can be seen (see Figure 3).

A third sign of fertility during ovulation is a change in the cervix. Before ovulation the cervix is low in the woman’s body, firm in texture and its opening (os), is closed. With the hormonal changes associated with ovulation, the cervix moves up in the woman’s body, becomes soft in texture and the os opens. Some STM methods do not require the observation of this sign of fertility.

Additional signs during ovulation include breast sensitivity; mid-cycle back pain, lymph node swelling in the groin; abdominal pain; and/or swelling of the vulva. When the presence of fertility signs is recorded on a chart, these secondary signs should also be noted and used to determine the event of ovulation.

As a direct result of ovulation, the hormone progesterone is produced by the body and changes the characteristics of the cervical mucus, making it thick and sticky. The woman’s body temperature also rises as a result of progesterone, and this change can be seen in the daily taking of the BBT. As described above, the first days of the BBT will be low (pre-ovulatory phase). A shift of about .4 F will occur after ovulation. The couple should observe six low temperatures prior to the Peak Day. After Peak Day, three high temperatures are recorded. The post-ovulatory (infertile) phase of the cycle is counted from the third high temperature after Peak until the onset of the next menses (the beginning of a new cycle). The post-ovulatory phase will last 10-16 days.

Achieving Pregnancy

The optimum time to achieve a pregnancy is from the onset of mucus until Peak day. The fertile phase continues until the woman experiences the third high temperature. A high temperature level sustained for 18‑20 days past Peak Day, confirms that conception has taken place. Knowing the exact time of conception assists physicians in determining the due date of the baby rather than guessing based on ambiguous data.

Avoiding Pregnancy

During the pre-ovulatory phase of the cycle, a woman must watch for the presence of cervical mucus. Days of dryness may be considered infertile and intercourse could take place in the evening of alternate nights. Alternate nights are used to ensure that any seminal fluid from the previous night’s intercourse has not masked the onset of cervical mucus.

If pregnancy is to be postponed or avoided, a couple should stop having intercourse or genital to genital contact as soon as mucus is observed, or a sensation of moistness is felt. Peak Day is identified as the last day of the most fertile sign, whether it is the last day of slippery, stretchy or blood tinged mucus or the last day of a lubricative, wet sensation. Peak Day cannot be reliably identified until the following day, when mucus undergoes a change due to the influence of progesterone. 

Sympto-Thermal Methods emphasize the relationship between at least two of the primary signs of fertility (for many, this is the BBT and the change in cervical mucus, see Figure 2). Whichever two primary signs first support each other, it is very important to make accurate observations, record them carefully, identify Peak Day correctly, and confirm the beginning of the infertile time.


The text above is authored by Stella Kitchen

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Other NFP Methods

In addition to the above two categories of now classic NFP methods, some scientists have developed other natural methods. Here’s a summary:

Researchers at the Institute for Reproductive Health at Georgetown University have developed two simple methods of NFP: the Standard Days Method and the TwoDay Method. The Standard Days Method (SDM) makes use of CycleBeads (a plastic ring of colored beads) to track the fertility of the woman’s menstrual cycle. The method is based on research of hundreds of women’s menstrual cycles. The SDM provides a formula for women who have cycles between 26 and 32 days in length. The days of the cycle that are considered fertile are days 8 through 19. If a woman has two cycles longer than 32 days or shorter than 26 days, she is advised to use another method of NFP. When used correctly the SDM is 95% effective for pregnancy avoidance. When not used correctly, the SDM is 87% effective for avoiding pregnancy.

The TwoDay method is based on cervical mucus. It makes use of two simple questions: 1) Did I notice cervical secretions today? And, 2) Did I notice cervical secretions yesterday? If the woman answers “No” to both questions, she can consider herself infertile. When used correctly, the TwoDay method is over 96% effective for avoiding pregnancy.

Researchers at the Institute for NFP at Marquette University have developed a natural method that makes use of an electronic hand-held hormonal fertility monitor and cervical mucus monitoring. The fertility monitor detects two reproductive hormones in the woman’s urine and provides information on three levels of fertility, i.e., low, high, and peak. The observation and charting of cervical mucus is used as a double check to the monitor’s readings. When used correctly, this Sympto-Hormonal method showed effectiveness rates of 98-99% for avoiding pregnancy. When not used correctly, the method is 87-90% effective.


The text above is authored by Richard Fehring, PhD, RN

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A Word About Effectiveness4

Effectiveness, as understood by the general public and family planning researchers, only refers to how well a family planning method can be used to avoid conception. NFP, on the other hand, can be used for both achieving and avoiding pregnancy.

As discussed in the previous chapters, NFP is very effective in helping couples identify the optimum time for conception. With regard to spacing or limiting pregnancies, NFP is up to 99% successful when couples understand the methods, are motivated, and follow their method's guidelines.5

The effectiveness of NFP for pregnancy avoidance depends upon spouses following the guidelines of the method according to their family planning intention (i.e., spacing or limiting births). Those who are strongly motivated to avoid pregnancy and follow the method strictly are very effective in meeting their goal.

Effectiveness of Natural Family Planning for Postponing Pregnancy6

  • Couples can achieve an effectiveness rate of 97-99% when they follow all the guidelines of their NFP method for avoiding pregnancy all the time (perfect use).
  • Couples can achieve an effectiveness rate ranging between 85-90% when they do not follow all the guidelines for avoiding pregnancy all the time (imperfect use).


4 “Effectiveness” as used here is a technical term. It is employed by researchers to indicate how well a family planning method can be used to avoid pregnancy.

5 See “Research in Natural Family Planning: A Review of Studies from 1998-2003,” in Current Medical Research, 14 (Summer/Fall 2003). For foundational studies, see Section II, “Effectiveness of NFP Method,” in Fehring and Kambic, Natural Family Planning Bibliography (1995): 9-12; available online here: Effectiveness of NFP Methods.

6 Research typically cites failure rates for “perfect use” as, 1-3% and for “imperfect-use” as, 10-15%. These failure rates are based on number of pregnancies among 100 couples in one year.


The text above is authored by Richard Fehring, PhD, RN

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NFP and the Couple’s Relationship

Couples who adopt NFP to space the births of children find that it brings about many positive changes in their relationship and even becomes a way of life. It begins with acceptance, and even wonder, at the way the human body is made. As one woman noted, “Knowing and learning about what goes on inside of my unique body amazed me.”6 Both men and women find this information empowering. One young husband commented after using NFP both to avoid and to achieve pregnancy, “I learned a lot about a woman’s body and conception...You know when you see all the things that go into conceiving a child it’s amazing.” The woman gains a new respect for herself and often finds that her husband has a new supportive attitude: “My husband respects me as a person in my own right. He accepts my fertility as part of me.” This new-found confidence contrasts with what one woman explained about how she felt using contraceptives: “I was required to sacrifice my health...I felt as if I were an object and not an equal partner in our marriage.”

Couples using NFP accept their fertility not as a nuisance or even a disease, but as a gift. When the physical pleasures of sexual intercourse are a couple’s primary focus, the woman especially can feel used. NFP treats the woman not as a sexual object, but as the unique person she is. NFP does not downplay the importance of sexual union and sexual pleasure. Through the practice of periodic abstinence NFP helps couples to find other ways in which to be attentive to each other in each cycle. These other ways may be through cooking a favorite dish or bringing home flowers. NFP can reignite the romance of dating for a married couple. As couples who use NFP often say: “Every cycle we have a wedding night.” When spouses love one another enough to abstain and be more considerate of each other, both become more secure in their relationship.

Periodic abstinence is difficult at times. It also brings its own reward. Men find they can direct sexual urges in the service of love and not be controlled by it. Only if a man is in full possession of himself can he love his wife well. As one husband said, “NFP has challenged me to self‑mastery so that I can freely give of myself.” The nature of married love is total self‑giving. If one is controlled by sex or withholds part of himself or herself (his or her fertility), that person cannot give totally to another. Self‑mastery, on the other hand, can actually enhance sexual pleasure. Many couples explain: “Giving our whole selves to each other intensified the sensations of pleasure and the feeling of unity in this expression of our love.”

When NFP is adopted as a lifestyle, fertility is regarded as a gift and children are valued and welcomed. A sense of awe at their power to procreate strikes many couples during the fertile time. One couple remarked that “NFP opened our hearts to children . . . Children are a gift, a blessing, not a burden.” Others have remarked that the time of fertility comes to be viewed with “a tremendous reverence” because fertility “is the time God created us to create.” When a couple knows the most fertile time in the cycle and tries to achieve pregnancy, it becomes a shared joy.

NFP instruction puts the emphasis on a couple’s shared responsibility not only for having children, but also for managing their combined fertility. Taking joint responsibility for fertility means that both spouses accept the challenge of abstinence during the fertile phase if they wish to avoid pregnancy. NFP requires couples to communicate. It helps them to talk about many things that may have been difficult to talk about before, including their sexuality. Through charting their fertility, they have a starting point for discussing the intimate aspects of their life, such as their sexual feelings and desires and their hopes or fears about pregnancy. Good, substantive interpersonal communication strengthens a marriage.

Many couples say that an NFP lifestyle deepens their faith in God. “(NFP) involved us with the Truth...We experienced...the conversion point in our lives.” “NFP is putting ourselves in God’s hands, totally allowing Him to work spiritually in our lives.” With so many rewards for those who persevere with NFP it would be surprising if there were not also challenges. As one husband says: “The reality is that NFP is challenging...[but] it is clear to me that working together through the tough times strengthens and enriches our marriage.” And as another spouse says: “The value I experience in NFP is in the long run...It forces you to place your immediate choices in the context of spouse, children, family and Creator.”

Benefits of NFP

  • Works with human fertility
  • Teaches a couple to understand their combined fertility
  • Treats each menstrual cycle as unique
  • Effective for achieving or avoiding pregnancy
  • Useful throughout a woman’s reproductive lifetime (e.g., post-partum, breastfeeding, perimenopause, etc.)
  • No harmful side effects
  • Economical (fees are typically charged for first instruction)
  • Values children
  • Helps parents teach their children about the meaning of human sexuality and the virtue of chastity
  • Requires mutual responsibility by both husband and wife
  • Encourages couple communication
  • Fosters respect for and acceptance of the total person
  • Respects God’s design for married love!


7 Couples’ quotes taken from Mary Shivanandan’s, Challenge to Love (Bethesda, MD: KM Associates, 1981) and Crossing the Threshold of Love, A New Vision of Marriage in the Light of John Paul II’s Anthropology. (Washington, DC: Catholic University of America Press, 1999).


The text above is authored by Mary Shivanandan, STD

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To find NFP classes in your area visit our Find an NFP Class page.

For distance NFP education, see our Home Study page.

For further information contact:

Natural Family Planning Program
United States Conference of Catholic Bishops
3211 4th St., N.E.
Washington, DC 20017
E-mail: @email

National Natural Family Planning Providers
The following providers offer NFP classes (in person and distance learning) for clients and teacher trainees.

Billings Ovulation Method Association—USA (a CMM provider; the official representative of the BOM in the USA)
P.O. Box 2135
St. Cloud, MN 56302
E-mail: @email

Couple-to-Couple League (a STM provider)
5440 Moeller Ave.
Suite 149
Cincinnati, OH 45212
1-513-557-2449 FAX
E-mail: @email

Family of the Americas Foundation (a CMM provider)
P.O. Box 1170
Dunkirk, MD 20754
1-301-627-0847 FAX
E-mail: @email

Institute for NFP, College of Nursing, Marquette University (a Sympto-Hormonal Method provider)
P.O. Box 1881
Milwaukee, WI 53201-1881
1-414-288-3838 or 3854
1-414-288-1939 FAX
E-mail: @email

Northwest Family Services, Inc. (a STM provider)
6200 S.E. King Road
Portland, OR 97222
1-503-215-7385 FAX
E-mail: @email

Pope Paul VI Institute for the Study of Human Reproduction (provides the Creighton Model FertilityCare™ System, a cervical mucus method)
6901 Mercy Road
Omaha, NE 68106
1-402-390-9851 FAX
E-mail: @email

About the Authors

Richard Fehring, PhD, RN, Director, The Institute for NFP, College of Nursing, Marquette University, Milwaukee; Emeritus Professor of Nursing, Marquette University; former member, NFP National Advisory Board, USCCB; science consultant to the NFP Program, USCCB.

Stella Kitchen, the late Director of the Southern Star NFP Program (an STM teacher training program); former member, NFP National Advisory Board, NFP Program, USCCB; former director of the NFP ministry for the Diocese of Harrisburg (PA) and the Diocese of Savannah (GA). 

Mary Shivanandan, STD, Emeritus Professor, The Pontifical John Paul II Institute for Studies on Marriage and Family, at The Catholic University of America, Washington, DC.

Theresa Notare, PhD, Assistant Director, Natural Family Planning Program, Secretariat of Laity, Marriage, Family Life and Youth, United States Conference of Catholic Bishops, Washington, DC.

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