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Modern Rhythm

Finding 'Safe' Sex Days
WebMD Feature
Reviewed by Craig H. Kliger, MD

Jan. 1, 2001 -- Nathan and Kathy Sendan begin each day with a pen, paper, and digital thermometer. The El Sobrante, Calif., couple dutifully record Kathy's basal body temperature before they even think of drinking their morning coffee. Then they combine the temperature readings with other physiological data to track Kathy's fertility cycle and, in effect, to time sex.

Such is the routine for those who practice natural family planning, a method that shuns hormones, condoms, and other artificial forms of birth control. It is the only form of contraception given the stamp of approval by the Catholic Church, but many proponents see a growing interest among non-Catholics as well.

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Joseph Stanford, MD, assistant professor of family and preventive medicine at the University of Utah and former president of American Academy of Natural Family Planning, estimates that as many as 40% of those now practicing this technique are non-Catholics. Natural family planning "offers an alternative where you don't have to mess up your physiology -- you're more in tune with your body, and there are no side effects," Stanford says.

"It's not just a Catholic thing anymore," says Patrick Homan, the western region field director for the Couple to Couple League, an Ohio-based institute whose 1,351 teachers offer instruction on natural family planning. "Our numbers have been going up for the last five to six years."

Indeed, the Sendans are not Catholic, but they chose natural family planning because of dissatisfaction with the pill. "I liked the idea of not putting chemicals in my body," says Kathy Sendan.

She recalls being "grumpy all the time" during the three years she was taking oral contraceptives. She also had a more specific health concern: "I have epilepsy, and the [antiseizure medication could] have made the birth control pill less effective," she says.

Numbers Remain Small

To be sure, the number of people choosing natural family planning still remains small. According to a 1995 survey conducted by the National Center for Health Statistics, only 1.5% of women aged 15-44 reported using periodic abstinence as a means of contraception. That trails the 17.3% of women choosing the pill, the most popular form of reversible contraception. Female sterilization was the most popular method at 17.8%, followed by the condom at 13.1%. Advocates of natural family planning say their efforts are hampered by the stigma of the "old" calendar rhythm method, which relied on the expectation that ovulation occurs on Day 14 of a 28-day cycle, and resulted in numerous "surprise" pregnancies.

In fact, menstrual cycles can vary from one woman to the next, and for many women, from one month to the next. Stress or illness, for instance, can disrupt even the most regular cycles. Such inherent variability was recently demonstrated in a study of 221 healthy women, published in the British Medical Journal in November 2000. Using daily urine tests to check for hormonal evidence of ovulation, researchers from the National Institute of Environmental Health Sciences found that even though clinical guidelines assume the average woman is fertile between days 10 and 17 of her menstrual cycle, only 30% of the women studied had their window of fertility fall entirely within that time period. Even women with reportedly regular cycles had a 10% chance of being fertile "on any given day of their cycle between days six and 21," the researchers wrote.

"What was surprising to us is the fact that not only were fertile days coming early in the cycle, but late when a woman thinks she's on the end of her cycle," says Allen J. Wilcox, MD, PhD, chief of epidemiology at the NIEHS and lead author of the study. "We're just putting numbers on something people had a sense of before."

The researchers also point out that most of the women in the study were between the ages of 25 and 35. Teenagers and women nearing menopause tend to have even more unpredictable cycles.

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