Monitoring Basal Body Temperature (BBT)

For women who are unsure of when they ovulate, keeping a basal temperature chart for several cycles may help predict the expected time of ovulation based upon the chart’s historical perspective. Basal temperature charts can help determine the expected mid cycle point, or time of anticipated LH surge, in order to determine when to start testing with an ovulation prediction kit.

The basal body temperature is one’s temperature upon waking up. The woman takes her basal temperature first thing in the morning before getting up and doing any other activity. The reading on the basal thermometer is recorded on a chart. By recording daily basal temperature readings on a chart for two or more months, a couple can gain historical perspective of the female’s time of ovulation within each cycle.

Beginning with the first day of menstruation, or steady flow, through the time preceding ovulation, a typical woman’s BBT will usually range between 97.2 degrees F and 97.6 degrees F up to 98.6 degrees F. On a Celsius scale, the reading will be between 36.2 and 36.4 C. From just after ovulation, at mid-cycle, through the beginning of menstruation, the BBT rises as much as one degree. Therefore, a woman’s temperature is lower during the first half of her cycle than during the last two weeks of the same cycle. This shift from a lower temperature to a higher temperature occurs around the time of ovulation. And is caused by an increased progesterone level after the follicle releases the egg. Keeping a written graphic record of daily basal temperature readings can therefore alert the couple to the time of ovulation.

Since the variation in temperature is slight (only a few tenths of a degree), it is essential that the temperature be taken with the most attention to accuracy. BBT can be taken orally (by inserting the thermometer in the mouth), rectally (by inserting the thermometer in the rectum) or vaginally (by inserting the thermometer in the vagina). The readings are typically the same regardless of the method you choose.