Now used by only about 5 percent of couples in this country, fertility awareness (along with male condoms) was for many years the preferred and sometimes the only method of contraception readily available. Fertility awareness uses the biological rhythms of the menstrual cycle; couples time intercourse for days when conception is unlikely to occur, and abstain from intercourse when conception is likely. The method works on the principle that you are most likely to get pregnant if you have intercourse around the time of ovulation, and it offers three ways of determining when ovulation occurs.
Fertility awareness is not a reliable contraceptive method and you should use it only if you would not be devastated by an unplanned pregnancy or cannot use other methods because of your religious beliefs. Any other method, including contraceptive foam, is more effective.
Because your fertility depends not only on when you ovulate but also on the life span of your partner’s sperm, which can live inside your body for as long as five and even seven days, an egg is more likely to be fertilized from intercourse that took place before or during ovulation than from intercourse after ovulation (though fertilization can happen a day or two afterward). You need to take this into consideration when planning your “safe” days.
The three techniques for predicting ovulation are the calendar method, the basal body temperature method, and the cervical mucus method. For maximum protection, you should use all three. All demand abstinence from sexual intercourse during a significant part of the month, and all demand accurate record keeping.
The Basal Body Temperature Method
The basal body temperature method works because your basal temperature (temperature at rest) falls during the twelve to twenty-four hours before ovulation; after ovulation it rises. By charting these changes, you can keep better track of when you ovulate. This method is quite accurate in documenting when ovulation occurs, but it is not so good in predicting when it will happen.
At a family planning clinic or pharmacy you can buy a special basal body temperature thermometer, for ten to twelve dollars, which comes with charts for recording changes. The scale runs from only 96 to 100 degrees Fahrenheit and shows small fluctuations in temperature. Or you can use a regular thermometer, which costs about a dollar.
Take your basal body temperature every morning before you get up — before you eat, drink, smoke, read the paper, watch television, or have sex. It doesn’t matter whether you take your temperature orally or rectally, though rectal temperatures are thought to be more accurate, but be consistent. Record the temperature on your chart and connect the dots, to make a graph showing the temperature changes throughout the month.
When the temperature falls, you are about to ovulate. When it rises (usually a half degree or a full degree Fahrenheit), you are ovulating or have ovulated. The rise may be sudden, making a spike on the chart, or it may be gradual, like steps. The pattern may change from one cycle to the next. Illness, emotional distress, jet lag, or even a poor night’s sleep can alter your basal body temperature. So can sleeping under an electric blanket or drinking more than your usual amount of alcohol the night before. Noting these events on your chart will help you interpret the results.
Which days are safe, according to the basal body temperature method?
After your temperature has risen and stayed up at least three days, you can assume your safe days have begun. These safe days last until the temperature drop that usually comes before your next menstrual period. You should consider unsafe all the days from the start of your period until the fourth day of the next temperature rise.
Why the long unsafe period? While the egg can only be fertilized for about a day after ovulation, sperm remain capable of fertilizing an egg for two or three days after ejaculation. If you have intercourse a couple of days before ovulation, there is a chance that lingering sperm will be available to fertilize the egg as it is released into the fallopian tube. Sperm can only survive eight hours in the vagina, but in the fallopian tubes they can live five to seven days.
How long should you chart your temperature before you begin using this method alone?
Chart your temperature for at least three months before you begin relying on this method. But it is much better to combine temperature charting with another method to help predict ovulation.