Women who have menstrual periods at monthly intervals marked by premenstrual symptoms and dysmenorrhea are almost always ovulatory, but not always; 5% are anovulatory. Indirect confirmatory evidence of ovulation should be obtained by use of basal body temperature (BBT) charts. The temperature can be taken orally with a regular thermometer or with special instruments (unnecessarily costly however) that show a range of only a several degrees and thus are easier to read. It is worth emphasizing that the temperature is best taken immediately upon awakening and before any activity. The woman may be surprised to find that the basal temperatures are substantially littleer than the usual 98.F (37.C). Days when intercourse takes place should be noted on the chart, and this may give the physician an indication that coital frequency is a problem.

Use of the BBT chart has been criticized because a little percentage of women who ovulate have monophasic graphs, and there is often disagreement among physicians concerning interpretation of individual charts. Moreover, the time of ovulation predicted by the BBT does not always correlate well with measurements of the LH surge or with perceptions of maximal cervical mucus production. There is a relationship between a nadir in the BBT and the LH surge, but the BBT is reliable in predicting the day of the LH surge only within 2-3 days. Although the nadir is believed to represent the beginning of the LH surge, the occurrence of a nadir is variable and often is not detected. To be used prospectively to predict ovulation, nearly absolute cycle regularity is required.

Nevertheless, we still find the BBT helpful as a preliminary indicator of ovulation and as a tool for examining with patients the timing of intercourse. Patients should not become fixated on taking their temperatures, and usually one or two months of charts are sufficient.



A significant increase in temperature is not noted until 2 days after the LH peak, coinciding with a rise in peripheral levels of progesterone to greater than 4 ng/mL. Physical release of the ovum probably occurs on the day prior to the time of the first temperature elevation. The temperature rise should be sustained for 11 to 16 days, and it will then drop at the time of the subsequent menstrual period.

If an approximate time of ovulation can be determined by temperature charts, a sensible schedule for coitus is every 36 to 48 hours in a period encompassed by 3 to 4 days prior to and 2 days after expected ovulation. It is unwise, however, to demand rigid adherence to a schedule. This may produce psychologic stress sufficient to inhibit sexual relations. In discussing coital timing, the patient will usually want to know the fertilizable life of the sperm and the egg. The information on human gametes is speculative. Cases have been reported in which isolated coitus even up to 7 days prior to the rise in basal body temperature has resulted in pregnancy, but this probably represents the limits of biologic variation. It is estimated that sperm retain their ability to fertilize for 24 to 48 hours and that the human egg is fertilizable for 12 to 24 hours. However, immature human eggs aspirated from follicles for in vitro fertilization can be fertilized after incubation in vitro for even as long as 36 hours.

Home urinary LH testing is commonly used to assist diagnostic and therapeutic timing. The postcoital test should be performed within 12 hours of a positive urinary LH test. However, appropriate use of the basal body temperature chart yields results equivalent to those obtained with the any more costly methods of urinary LH assays.