An objective method for detecting the shift in basal body temperature in women.

The upward shift in basal body temperature (BBT) observed in women of child-bearing age is often used as an indicator that ovulation has occurred and that a period of infertility has begun. In natural family planning programmes it is important to detect the BBT shift reliably and with a minimum of user uncertainty, against a background of physiologically induced temperature variations. The cumulative sum (CUSUM) test is adapted to the problem of detecting BBT shift and applied to 137 BBT charts obtained from 21 women using natural family planning. Results show successful detection of the shift in all cases. Shifts occurred at gynaecologically appropriate times in the menstrual cycle.