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Article in Scientific American

March 26, 2007

Modified Rhythm Method Shown to Be as Effective as the Pill—But Who Has That

Kind of Self-Control?

Depending on whom you ask, not having babies is easier, or harder, than ever

By Mims

For years the birth control methods collectively known as periodic

abstinence have been jokingly referred to as " Vatican roulette, " a nod to

the fact that these techniques are both Vatican approved and quite likely to

end in pregnancy. (The World Health Organization reports that on average,

women practicing periodic abstinence for a year have a one in four chance of

becoming pregnant.)

A new German study, however, has found that, when practiced correctly, a

method of periodic abstinence known as the sympto-thermal method (STM) leads

to an unintended pregnancy rate of only 0.6 percent annually. This rate is

comparable with that of unintended pregnancies in women who use birth

control pills, the most popular method of contraception in the U.S.

For the sympto-thermal method to work, women must keep track of three

things: their core body temperature, the fertile days of their cycle as

measured by a calendar, and their cervical secretions. Using this

information, women are able to abstain from sex during their fertile period,

which is the two weeks that surround the day on which they ovulate.

According to lead study author Petra -Herrmann, a fertility researcher

at the University of Heidelberg in Germany, STM is more effective than the

other so-called periodic abstinence methods because it uses more than one

type of information to predict the dates of a woman's fertile period.

As effective as STM can be, experts say it is not right for everyone.

Whereas the method is cheap (read: free) and appeals to women who want a

natural birth control method, it requires a strong commitment on the part of

both partners.

" You really can't extrapolate from this paper, " says Grimes, an

obstetrician-gynecologist and vice president of biomedical affairs at the

nonprofit public health organization Family Health International. " Naive

readers see these results, and they think [sTM] is the greatest thing since

laptop computers. The researchers on this paper went back and cherry-picked

this data from an ongoing study from the past 20 years. They chose the users

who were the best users for this method. "

Hilda Hutcherson, an ob-gyn and co-director of the New York Center for

Women's Sexual Health at New York-Presbyterian Hospital/Columbia University

Medical Center, found that her patients often stop using periodic abstinence

methods after only a few months. " It's difficult to abstain from sex for two

out of four weeks, " she says. " That means half the month you can't have sex.

That's very difficult for young couples. "

Grimes of Family Health International believes that studies of periodic

abstinence are often motivated in part by religious beliefs. " Many of the

authors of these studies have religious orientations, " he says, " and that

clouds the motivations. " Some 74 percent of the women who participated in

-Herrmann's study, which will be published in the journal Human

Reproduction, listed their religion as Roman Catholic, a faith for which

this is the only church sanctioned method of family planning.

But Suzanne Parenteau-Carreau, a researcher and an advisor at Serena, a

Canadian volunteer organization devoted to teaching couples how to practice

the method, disagrees. She says that although religion was the early

impetus, couples who practice STM are now seeking " natural'' birth control.

" Now it's more and more from a natural motivation; to be closer to nature, "

she says. " We often say it's people who like camping, bicycling, outdoor

exercise—people who want healthy food and healthy natural family planning. "

But that notion irks Grimes, who insists it is misleading. " I chafe at the

term 'natural family planning,' " he says. " For many couples this is highly

unnatural. 'Natural' is methods that you don't have to think about, that

allow you to be spontaneous…. STM is very unpopular, hard to use, and has a

poor success rate in average couples. Most people aren't willing to put up

with it. "

-Herrmann acknowledges that one U.S. study conducted in 1980 in Los

Angeles had a 90 percent dropout rate after less than two years.

But Grimes concedes that STM has its advantages, chief among them that " it

is cheap, safe and approved by the Roman Catholic Church…. It is a

reasonable part of the mix of contraceptive methods, it's just that for most

people it's not an acceptable method. "

Whether or not this method will ever gain ground on other contraceptive

methods—the most recent data available indicate that less than 1 percent of

women who use birth control in the U.S. use any method of periodic

abstinence—all observers agreed that STM can only work for couples who stick

to the plan 100 percent.

" It's not for everybody, " -Herrmann notes, " but there is a group of

women who are interested in this method, and I think we should offer it to

them. "

The bottom line: all contraceptive methods have their drawbacks, including

the potential of passing along the HIV virus and sexually transmitted

diseases best prevented by condoms. Ultimately, Grimes says, " the best

method for a couple to use is whatever they want. It's counterproductive to

try to steer people to one thing or another. "

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