The reliability of ovulation prediction by a single ultrasonographic follicle measurement

Since ultrasonographic ovulation detection has been introduced many authors have speculated about the ovulation predictive value of this new technique. Reliable studies in this respect, however, are lacking. The present study describes ultrasonographic data of 158 spontaneously ovulating, infertile patients. Each patient contributed only one cycle to the study. To construct individual follicle growth curves serial follicular measurements were performed. A wide range existed in mean maximum diameters of the preovulatory follicles. Furthermore, the slopes of the follicle growth curves, as well as the durations of the follicle growth phases showed considerable variations. The intrinsic variability in the various characteristics of follicle growth makes a single measurement as accurate as serial measurements in predicting ovulation. A formula has been devised by means of the data of the first 100 women, which correlates follicular diameter with the time interval to ovulation. The formula was developed based on one randomly selected measurement per patient. The validity of the formula has been tested in 58 additional women, also contributing one measurement each. According to this validation the adequacy of the prediction rule was demonstrated. Ultrasound appeared to be a less sensitive method for prediction of ovulation than has been speculated by some investigators. It is, however, an improvement, compared to the prediction of ovulation based upon the length of the previous menstrual cycles. A single follicle measurement may therefore be helpful in timing post-coital tests or artificial inseminations, in addition to being an adjuvant to more reliable methods.