As a Catholic theologian, I am aware that the Catholic Church tends to be so promotional of NFP as to neglect to inform users that, as in all medical advice, there are potentially dangerous “side effects” to the use of NFP. This practice is unfortunate. It destroys confidence and subverts “honesty in advertising.”

Consider, for example, the medical advice given to patients by The American College of Obstetricians and Gynecologists:

Q.   How effective is NFP in preventing pregnancy?

A.   Natural family planning is not as effective as most other methods of birth control. One in four women who use this method become pregnant. The method is not suited for the following women:

• Women who should not get pregnant because of medical reasons

• Women with irregular menstrual periods who may not be able to tell when they are fertile

• Women with abnormal bleeding, vaginitis, or cervicitis (these make the cervical mucus method unreliable)

• Women who use certain medications (for instance, antibiotics, thyroid medications, and antihistamines) that may change the nature of vaginal secretions, making mucus signs impossible to read

• Women with certain problems unrelated to fertility (for instance, fever) that can cause changes in basal body temperature  (source)

If our  bishops would include these on a “warning label” with their NFP promotional pitches, then Catholic women who suffered through unwanted pregnancies would feel relieved that it was not their fault that they got pregnant while using NFP.  Meanwhile, those considering using NFP for the first time would be encouraged to know that the bishops are straight shooters and that they are not blinded by ideological and theological factors.

As things now stand, the glowing testimonials in favor of NFP are motivated by the “unspoken truth” that NFP is currently the ONLY OFFICIALLY APPROVED method for regulating pregnancies.  Hence, Catholics who want to believe that Paul VI could make no major error in drafting Humanae Vitae will want to do fancy cartwheels to demonstrate  that he was 100% right about NFP.

Consider this, for example.  When you visit the  cheerful site known as Catholic Online,  you will hear a Catholic mother of six explaining how she came to hold fast to NFP.   Along the way, however, she makes some pretty fantastical claims:

When women learn to read their cycles, they often report a renewed sense of self-worth. . . .  Women often can’t place their finger on it, but they sense this. Not surprisingly, couples who practice a method of NFP have only a 5% rate of divorce by comparison to the 50% rate in the population at large. Clearly, when couples treat one another with dignity and respect, honoring the wholeness of each person, their relationship is positively effected.

I say “fantastical” because if the text in red were true, then sex therapist and couples counselors would have used this info by way of shoring up sagging marriages everywhere–and not just among Catholics.  Yet, if it seems too good to be true, it probably is not true.   And this unfortunately is the case, despite the fact that I have heard this claim routinely used in NFP  promotionals.   Hence, this is something like being told to take huge doses of vitamin C to prevent the onset of the common cold.  “Every belief works in the eyes of the believer” (Michael Polanyi).

Mark Twain — ‘What gets us into trouble is not what we don’t know. It’s what we know for sure that just ain’t so.’

Fraternally,

Aaron Milavec

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I did an AI search and discovered some things that I never knew before regarding the effectiveness of NFP.  Here it is:

1. “The influence of ever‐use of Natural Family Planning and contraceptive methods on divorce rates among Catholic women”

Rodriguez, Fehring, et al. (2013 NSFG data, Journal of Catholic Health Studies)
This analysis used data from the 2006–2010 U.S. National Survey of Family Growth (NSFG) to compare marital stability among 1,502 Catholic women who had ever used NFP (e.g., mucus or temperature methods) versus those who used hormonal contraception or sterilization. Key findings include:

• Catholic women who had ever used NFP showed a 9.5% divorce rate, compared to 18.3% among those who never used it, yielding an adjusted odds ratio (OR = 0.47; 95% CI: 0.24–0.91), indicating 53% lower odds of divorceen.wikipedia.org+5epublications.marquette.edu+5guttmacher.org+5usccb.org.

• Sterilization correlated with more than double the odds of divorce (OR = 2.41; 95% CI: 1.82–3.20), while pill use showed no significant effectusccb.org.

• Frequent church attendance also reduced divorce risk (OR = 0.66)reddit.com+15epublications.marquette.edu+15usccb.org+15.

Limitations: Self‑selection bias (NFP users may be more religious/committed), cross-sectional design limits causal inference, and “ever-use” lacks detail on duration or fidelity. Authors caution interpreting results beyond correlation as divorce may be influenced by religiosity or marital commitment, not solely NFP.

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2. “Natural family planning: effective birth control supported by the Catholic Church”

R.E. Ryder (BMJ, 1993)
This paper reviews clinical studies worldwide on cervical mucus-based NFP, emphasizing its effectiveness and promoting it for global use. Main points:

• WHO data indicate 93% of women across diverse cultures can accurately identify ovulation via mucus patterns.

• Pregnancy probability after intercourse outside fertile periods was just 0.4%, while near ovulation it rises predictablypubmed.ncbi.nlm.nih.gov.

• A large survey of 19,843 low-income Indian women using mucus-based NFP reported nearly zero pregnancy rate, comparable to combined oral contraceptivesepublications.marquette.edu+12pubmed.ncbi.nlm.nih.gov+12hli.org+12.

• NFP was celebrated as cheap, side-effect-free, culturally acceptable, and empowering—especially in resource-limited settings.

Limitations: Effectiveness depends heavily on perfect use and motivation; critiques highlight that “perfect-use” efficacy is unattainable in general populations. Method effectiveness varies by instruction quality and user adherence.

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3. “Comparisons of marital, sexual, and spiritual dynamics among Catholic couples using NFP vs contraception”

Fehring & Kurz (2007, USCCB report + supporting research)
This study synthesizes small-scale comparative research (~22 NFP couples vs ~22 contraceptive couples) on relational and spiritual outcomes:

• Over 75–85% of NFP users reported enhancements in marriage intimacy, communication, spiritual well-being, trust, and self-controlusccb.org+3uffl.org+3hli.org+3.

• Couples said periodic abstinence fostered appreciation for each other, though 42% reported challenges with spontaneity, scheduling sex, or fear of unintended pregnancyuffl.org.

• Small studies also found NFP users reported higher self-esteem than those using contraceptivesusccb.org+11uffl.org+11hli.org+11.

Limitations: Non-randomized, small samples, and potential self-selection bias—motivated couples may both prefer NFP and have healthier relationships. Lack of long-term or large-scale comparative data limits external validity.

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🔍 Summary & Takeaways