How does the Basal Body Temperature Method of natural family planning work?
The temperature is obtained orally after at least six hours of sleep prior to rising (placing the special basal body temperature thermometer into a cup containing the first voided urine sample is a simple way to do this). Following the postovulatory elevation of progesterone, the temperature should rise by at least 0.5C. Although this temperature rise is a consequence of ovulation, not a predictor, it may reveal a pattern for future cycles. It also confirms that ovulation has already occurred and, therefore, the fertile period will end shortly (48 hours later). Since other factors can cause a temperature elevation, resumption of unprotected intercourse too soon after the presumed “ovulatory temperature rise” may lead to unintended pregnancy. Unprotected intercourse should be delayed until at least three consecutive days of raised temperatures have been documented. Up to 20 percent of women with documented ovulation may not show a biphasic basal body temperature (BBT) chart and therefor
