If you're going the natural route for birth control, you'll probably be better off combining two methods rather than depending on only one, suggests health expert Dr. Weil.

For example, the cervical mucus method can be 98 percent effective when used in conjunction with the temperature method.

• Cervical mucus: This involves checking the amount and texture of your cervical mucus, a vaginal discharge that reflects estrogen levels at various points in the menstrual cycle. Just after menstruation you probably won't notice any cervical mucus at all. Later, you'll see a cloudy, sticky mucus. When this increases in volume and resembles raw egg white, ovulation is near. As soon as you notice this change, be sure to avoid intercourse until four days after you observe that the mucus is again cloudy and sticky or has disappeared altogether.
• Temperature: This approach involves taking your temperature with a special "basal" thermometer as soon as you wake up in the morning. Your normal temperature probably will range from 97.2 to 97.7 degrees before ovulation. The hormonal changes prior to ovulation boost basal body temperature; you'll see an increase of 0.5 to 1.6 degrees. When your temperature is elevated for at least two days, you'll know you are ovulating and should avoid intercourse. You can resume having sex when your temperature returns to normal.
• Calendar Method: If your menstrual cycle is very regular, you could try the "calendar" method, which involves avoiding sex during the week that you believe you're ovulating. To do this right you'll have to first track your periods for a year. Then to figure out when you might be fertile, subtract 18 from the number of days of your shortest cycle in the past year. This is the date on which you should stop having sex. To calculate when you can resume, subtract 10 from the number of days in your shortest cycle. Used on its own, the calendar method has a 75 percent success rate.
• Withdrawal: This method requires the man to withdraw his penis from the vagina before ejaculation. This is the least reliable of the natural methods: only 60 to 80 percent successful.

You also have the option of using a diaphragm or condoms. Used consistently, diaphragms are 84 percent effective when used in conjunction with a spermicidal cream; condoms are 97 percent effective when used consistently and correctly and have the added advantage of protecting against sexually transmitted diseases.