A New Bead on Birth Control

This approach just might appeal to women who don't want to take the pill or can't do so (because of a history of blood clots, for example), or who are put off by a barrier method of contraception, or who are religiously opposed to medical contraception, says Lawrence B. Finer, associate director for domestic research at the Alan Guttmacher Institute in New York.

The Georgetown system did appeal to Amy S. Adams, 27, a database coordinator in Lynchburg. She seriously considered going on birth control pills last December, "but you hear about the mood swings and weight gain and all that kind of stuff with the birth control pill," she said. "I decided that wasn't something that I wanted to deal with."

Regular condom use also didn't appeal to Adams and her new husband, Robbie. The couple married in May, and "we don't want to take away from the intimacy of [sex]," she explained. So she hit the Internet, found CycleBeads, and bought herself a set. They sit on her dresser now, and Adams advances the gasket across the beads each morning. When she's in her "white bead days," she says, she warns her husband, "Honey I'm fertile today, so we have to be extra careful. . . ."

So far, Adams is pregnancy-free. "We knew there was a balance, and we were determined to find that," she said. "I feel really confident that this method really works."

The Wild Egg Chase

Throughout history, women who have relied on avoiding unprotected sex at certain points in the month to prevent pregnancy have been sorely disappointed.

Until recently, medical experts have had a poor track record at pinpointing when a woman is likely to ovulate each month. In the late 19th century, doctors assumed that women ovulated just before menstruation, as many animals do, explains Andrea Tone, a professor in the social studies of medicine at McGill University in Montreal.

"Doctors advised women wishing to avoid pregnancy to have intercourse only mid-cycle," said Tone, the author of "Devices and Desires, A History of Contraceptives in America" (Hill and Wang, 2001). This meant that women were advised that pregnancy was unlikely at precisely the moment when they were most likely to conceive.

"You can imagine the results," she said.

It wasn't until the 1920s that surgical retrieval of eggs from the fallopian tubes revealed that women tend to ovulate sometime around the middle of their cycle. But to prevent pregnancy, doctors needed to be able to predict the timing with more precision. They also needed to know how long before and after ovulation a woman remained fertile. Complicating the question was the knowledge that most women's cycles vary slightly each month with changes in eating, exercise, sleep and stress.

In addition, doctors weren't sure of the shelf life of sperm and egg: If intercourse occurred a few days before ovulation, how long could the sperm survive inside a woman's body to fertilize the egg? If intercourse occurred after ovulation, how long might an egg still be able to be fertilized?