The hypothalamus signals the pituitary gland (via the GnRH hormone) to release a surge of luteinizing hormone (LH) which causes ovulation approximately 36-42 hours later. Normal, regular, ovulation (ideally with a menstrual cycle of less than 32 days) is ideal for establishing a pregnancy. Intercourse should occur around the time of ovulation to provide the optimal chance for conception.
The basal body temperature chart (BBT) was used to predict ovulation. Using this method, the body temperature (using a basal thermometer) is taken every day prior to getting out of bed and entered on a chart and graphed. This is done daily and a slight decrease (0.2-0.3 degrees on the day of ovulation) followed the next day by a slightly greater rise (0.5 degrees) in temperature will be seen on the day after ovulation.
These charts are recorded for several months to establish an ovulatory pattern. Once the ovulation history is determined, the chart can be used to help predict future ovulatory time frames. For women with regular cycles it can be approximately 80% accurate. The main advantage is that it is inexpensive. BBT charting can be time consuming and sometimes frustrating due to its relative inaccuracy.
Several Websites now provide computerized charting and graphs. It is important to realize that the temperature does not rise until after ovulation has occurred (too late for optimally timing intercourse that month). The charts can be useful for analysis of the cycles (start of menses, days ovulation predictor kits (OPK) tests were done, dates intercourse occurred, length of the presumed luteal phase, next menstrual start date, etc).
BBT charting is used less frequently now with most physicians recommending the urinary LH test kits or hormonal tests. The kits accurately (approximately 90-95%) measure the spike in LH that precedes ovulation allowing couples to time intercourse, IUI or cycle related testing.
One indicator of successful ovulation is an increase in progesterone levels. Progesterone is produced by the leftover follicular structures known as the corpus luteum. Low progesterone levels are an indication that “quality” ovulation did not occur.
Sometimes the vaginal probe ultrasound in conjunction with blood testing for estradiol (E2), progesterone (P4) and luteinizing hormone (LH) is used to help document ovulation. The fertility specialist scans the ovaries prior to ovulation and visualizes the follicles. After the predicted ovulatory time, the ovaries are examined again to establish that the follicles ruptured and released their eggs.