Improved prediction of postovulatory day using temperature recording, endometrial biopsy, and serum progesterone

The use of basal body temperature (BBT) recording and a single progesterone (P) level at the time of the endometrial biopsy in the late luteal phase improved our ability to predict the onset of the next menstrual period (NMP) and determine the postovulatory day (POD) in 124 regularly menstruating infertile women. We determined BBT shift using a microcomputer program, analyzed P levels by radioimmunoassay, and evaluated endometrial biopsies both prospectively (blinded) and retrospectively (with knowledge of the other variables). Serum P levels were within the normal range for the luteal phase and prospective and retrospective histological diagnoses closely agreed (82% within 2 days). The best correlation with the NMP was the BBT shift (r = 0.493) followed by P (r = 0.426) and prospective histologic dating (r = 0.390). Multiple regression analysis confirmed that use of all of the variables markedly improved the ability to estimate the POD (R2 = 0.51).