As a teenager, Susan began taking “The Pill” to help regulate her menstrual cycle. Once married, she appreciated the “convenience” of it — an opportunity to enjoy the privileges of matrimony without the worry of changing diapers too soon. But, tired of pill-popping and the physical wear and tear that comes with the daily intake of synthetic hormones, Susan decided to take back her fertility, and she and her husband learned natural family planning. “The rewards — including marriage-building and knowledge of one's body — are so worth it.”

Susan is not alone. Among the couples she knows who use natural family planning, many of whom she met over the Internet, most say it's “easy.” She and her natural family planning-using friends — many of whom left the world of artificial hormones because of the havoc it had already wreaked on their bodies — also share a complaint often heard among those who've discovered natural family planning: Why didn't anyone ever tell me sooner?

Call it the world's best-kept family planning secret. It has long been derided and caricatured as part of a patriarchal Roman Catholic understanding of human sexuality. (The old joke is: What do you call couples who use natural family planning? Parents.) Now, natural family planning may be ready to go prime time, showing up in places like the Vegetarian Times, attracting an audience interested in going natural. Ironically, it may be the increasing numbers of brands of artificial contraceptives — most of which come with their own set of potential side effects, including threats to future fertility — available at their local pharmacies that are driving women to abandon pills, rubber, creams and jellies for nature's own.

It's not just Catholics who are signing up for natural family planning classes. “The large numbers of those who have turned to natural methods are not doing so for religious reasons,” says Rosalie Wesley, director of research at the Institute for Reproductive Health at Georgetown University in Washington, D.C.

“I would say that starting 10 years ago we were probably talking about 80 to 90% [of people learning natural family planning] were Catholics and now it is probably closer to 60%,” Joseph Stanford, former president of the American Academy of Natural Family Planning, recently told the Boston Globe.

Robert Kambic, a researcher who focuses on natural family planning at Johns Hopkins University in Baltimore, has been teaching natural family planning with his wife since 1970. In his experience, religion is rarely the catalyst for learning natural family planning. “In our 30 years of pre Canas, we always stress the lack of side effects, health, ‘understand self,’ ‘understand sexuality,’ ‘work together to plan and space pregnancies.’ These are the things that people come in wanting to know.”

And, although far from being cheerleaders, the reproductive-rights crowd can't rule natural methods of family planning out of the smorgasbord of available birth-control options. When asked, Princeton University's James Trussell, long-time editor of the field's bible, Contraceptive Technology, admits that while natural family planning methods are “very unforgiving of imperfect use,” “they are quite effective when used correctly and consistently.”

Still, granting institutions are rarely willing to fork over much money for research and development — nor are HMOs always willing to cover natural family planning classes, which usually run at a little over $100.

Pinpointing the actual numbers of natural family planning users is a challenge. According to the 1995 National Survey of Family Growth, 3% of all those limiting their family size in the U.S. chose natural family planning to do so. Georgetown's Institute for Reproductive Health, which focuses exclusively on natural family planning methods worldwide, finds that among married women who use any family-planning method, 14% use some form of periodic abstinence.

But interpreting the numbers is difficult. The World Health Organization considers natural family planning to be “methods for planning and preventing pregnancies by observation of the naturally occurring signs and symptoms of the fertile and infertile phases of the menstrual cycle, with the avoidance of intercourse during the fertile phase if pregnancy is to be avoided.”

In keeping with that definition, the limited numbers of surveys extant with a focus on natural family planning, lump together couples using the old, fairly obsolete rhythm method with those using withdrawal, and those using the much more structured Sympto-Thermal and Creighton methods, which require training in identifying cervical mucus in relation to fertility and temperature-taking. Surveys on pregnancy rates also fail to discriminate between those using natural family planning methods to avoid pregnancy and those who are simply trying to space out their children.

Still, despite the problems with surveys, a year-old, much-lauded study in the Journal of Reproductive Medicine proved what natural family planning doctors, teachers and users have long claimed.

Among some 2,000 couples using the most popular of methods, the Creighton model, the effectiveness rate was comparable to the pill or the condom. But don't expect natural family planning to become a viable option in sex-ed courses, since, in keeping with its religious roots, it is not “contraception” in the usual sense.

Natural family planning is meant to be divorced from the contraceptive mentality, rather than from procreation. It doesn't protect against sexually-transmitted diseases, nor is it an alternative for the promiscuous, who presumably don't have much flexibility in planning their dalliances.

And it still has its public-relations problems. Natural family planning is branded, tied very directly in public opinion to the Catholic Church and its opposition to abortion and contraception. And as the contraceptive mentality has been absorbed by people of all denominations, a sense of defeat on the issue among Catholics may have settled in, too.

Despite his dedication to natural family planning methods, on both theoretical and practical levels, Robert Kambic is skeptical about claims of a newfound popularity for natural family planning. “My wife and I have always seen this before — people coming to this just because they think it is a good thing — not for religious reasons. These new, younger people see things a little more short term. They see things positively.”

And, he faults his beloved Church for the lack of enthusiasm and understanding among her flock for natural family planning. Until the Church jumps in with financial support for advertising and education, and even full-time coordinators in dioceses that don't have them, a significant increase in Catholics using natural family planning is a far way off.

Kathryn Jean Lopez is production editor for National Review.