Which of the following method is the best predictor for ovulation in a female infertility patient during a menstrual cycle

In the anovulatory cycle, plasma progesterone reaches a peak of 15ng/ml at mid-luteal phase (22-23days). Basal body temperature (BBT) falls at the time of ovulation by about 1/2degree. During the progestational half of cycle, the temperature is slightly raised above the preovulatory level. But it is now obsolete because: Tedious daily recording Not very accurate Better modalities are available In endometrial biopsy endometrium from the uterus is curetted preferably 1 or 2days prior to the onset of menstruation. Histological examination done for secreatory changes. Now a days endometrial biopsy is omitted as a routine investigation of infertility. Only used in suspected tubercular endometritis Fern test: cervical mucus is examined under a low power microscope. During estrogenic phase, it shows a charecteristic fern patten which disappears after ovulation