Everyone knows the basics of conception: Sperm meets egg, and nine months later a baby is born. But many women don't understand the body's subtle fertility indicators. By learning about fertility awareness, however, women can acquire a useful tool for either aiding conception or preventing pregnancy.

Unlike the rhythm method, which estimates ovulation based on the length of a woman's cycle, fertility awareness is reinforced by daily observation and can work for those whose cycles vary from month to month. "Many women are taught that ovulation occurs on day 14 of their menstrual cycle," says Toni Weschler, author of Taking Charge of Your Fertility. "When it doesn't, they miss their chance to conceive, or misjudge the safe time of the month and conceive accidentally."

THE BODY'S MESSAGES

Here's how fertility awareness works: Early in your monthly cycle, several days after menstruation ends, rising estrogen levels trigger the release of cervical mucus. Throughout the cycle, the mucus increases in volume and changes in texture. You're most fertile -- in other words, you're most likely ovulating -- when the mucus is clear, slippery, stretchy, and resembles raw egg white. This kind of mucus allows sperm to enter the uterus and swim toward the fallopian tubes. After ovulation, an increase in progesterone makes the mucus scant and pasty, blocking the sperm's path through the cervix. Body temperature also offers clues to fertility: It rises about half a degree immediately following ovulation and remains slightly elevated until the start of your next menstrual period.

As a means of facilitating conception, fertility awareness is an effective, low-tech approach that sometimes prevents the need for fertility treatments. Michael Zinaman, M.D., director of reproductive endocrinology at Loyola University Medical Center in Maywood, IL, recommends that a woman check her cervical mucus and chart her temperature for one month to establish her regular pattern. "The next month, she continues to chart her cycle but can refer to last month's record to pinpoint the day she's likely to ovulate," Zinaman says.

Mucus is easy to observe by wiping with toilet tissue before urinating or by doing the stretch test: With mucus between forefinger and thumb, spread your fingers apart. The longer the mucus stretches before breaking, the more likely ovulation is near. To track your temperature, use an oral basal body thermometer (it's more sensitive than an ordinary thermometer) and take your temperature first thing each morning before you get out of bed, use the bathroom, drink, or eat. When you pinpoint an ovulation pattern, experts recommend that in order to conceive, you have sex at least every other day once mucus discharge begins, including the day you're due to ovulate.

THE ABSTINENCE FACTOR

Using fertility awareness as birth control, on the other hand, can be tricky. When it's practiced properly, the method works 85 percent of the time, according to Zinaman (the diaphragm, by comparison, offers 82 to 94 percent protection). If you're trying to prevent pregnancy, you'll need to either abstain from sex or use a barrier method from the time you spot any mucus until four days after it's changed from an egg-white to a pasty consistency and your temperature has risen -- up to ten days a month in all. In addition, new mothers are strongly advised to use a backup contraceptive because mucus patterns are less reliable right after giving birth and while breastfeeding.

Despite the method's flaws, however, many women are convinced that it's well worth the trouble. "It's just as easy to take your temperature every morning as it is to take a pill every night," says Seattle mom Gwen Eakers, who conceived her daughter through fertility awareness and now uses it as birth control. But she admits that the method requires motivation and commitment from both partners: "If you're not disciplined, it's going to be pretty difficult."

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