Temporal relationships between ovulation and defined changes in the concentration of plasma estradiol-17 beta, luteinizing hormone, follicle-stimulating hormone, and progesterone. I. Probit analysis. World Health Organization, Task Force on Methods for the Determination of the Fertile Period, Special Programme of Research, Development and Research Training in Human Reproduction.

One hundred seventy-seven women have been studied over the periovulatory period, in order to obtain detailed information on temporal relationships between ovulation and defined changes in the concentrations of estradiol-17 beta (E2), luteinizing hormone (LH), follicle-stimulating hormone (FSH), and progesterone (P) in peripheral plasma. Serial samples of blood were taken, the surfaces of the ovaries were examined at laparotomy, and the mature follicle or corpus luteum was removed for histologic examination. The results in 107 cases fulfilled the criteria for statistical analysis, and in 78 the operation was performed after the follicle had ruptured. A probit analysis was undertaken with use of the proportion of women who had ovulated at a given time in relation to the interval from a defined rise or peak in the concentration of a circulating hormone. The median time intervals (in hours) from the hormonal event to ovulation and the 95% confidence limits of the estimates are as follows: 17 beta-estradiol--rise 82.5 (54.0 to 100.5), peak 24.0 (16.9 to 32.1); LH--rise 32.0 (23.6 to 38.2), peak 16.5 (9.5 to 23.0); FSH--rise 21.1 (14.1 to 30.9), peak 15.3 (8.1 to 21.7); progesterone--rise 7.8 (-12.5 to 15.9). From the statistical model for LH it was possible to estimate that ovulation in 90% of the cases had occurred between 16 (+/- 6) and 48 (+/- 6) hours after the first significant rise in the concentration of this hormone and between -3 (+/- 5) and 36 (+/- 5) hours after the peak. An examination of the individual results in every woman gave corresponding ranges of between 24 and 56 hours from the first significant rise in LH and between 8 and 40 hours after the peak. From a practical standpoint, the conclusion is that a defined rise in the concentration of circulating LH is the best indirect parameter of impending ovulation.