Some years ago, when I was pregnant with my daughter, now 18, I remember a friend of mine and her husband decided it was time to start a family. On a visit to the gynecologist we shared, she asked if there was any time during her cycle that was better for having sex to maximize her chances of becoming pregnant. The doctor looked at her oddly and said, "I think any time your husband feels like sex is the right time." Answers like that eventually led both of us to change doctors, but even today women are shockingly ignorant of what their body may be telling them about when they're fertile.

Whether you're trying to get pregnant or trying to avoid pregnancy, understanding your cycle and when you are fertile can help you achieve your goals. More important, notes Toni Weschler, author of Taking Charge of Your Fertility (Perennial, 1995), it's empowering to be knowledgeable about such a fundamental part of being a woman.

If you're trying to start a family, understanding your cycle can expedite the process by helping you pinpoint when you ovulate. This is particularly important for women who don't have a perfect 28-day cycle – in other words, the vast majority of women. "The whole concept of a 28-day cycle with ovulation on day 14 is a myth that has been entrenched in our culture," Weschler says. "The fact is that some women may ovulate on day 10 and some on day 30. If you're having sex around day 14 in an effort to get pregnant, but you're not ovulating for another week, you're not going to be successful."

Understanding your cycle and when you're most fertile also gives you the tools to make some fairly quick judgments about whether it may be necessary to seek fertility counseling, rather than waiting the year that most doctors recommend.

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