Using corpus luteum formation with dominant follicle collapse to improve the criteria for identifying the day of ovulation

Research Questions: (1) Does corpus luteum formation help to identify day of ovulation on ultrasound when follicular collapse is missed?(2) How reliable are sonographers versus a review panel in identifying the day of ovulation on ultrasound?Design: Sonographers in a clinic in Canada performed serial endovaginal ultrasounds (6-8 per cycle) to identify the day of ovulation in regularly cycling women (n=40) who were followed for 1 to 5 cycles (n=85).The day of ovulation was identified by: (1) identification of the dominant follicle, (2) disappearance of the dominant follicle, and (3) identification and dating of the corpus luteum.The main outcome measures were inter-rater reliability between two sonographers and Bland-Altman agreement between the supervising sonographer and a panel that reviewed each scan to identify the day of ovulation.Results: Of the 85 menstrual cycles reviewed, 2 cycles did not have sufficient data to date ovulation, one showed an incidental dermoid cyst and 11 cycles showed anovulatory patterns.This left a total of 71 cycles (84%) for which intra-rater reliability between two sonographers for identifying the day of ovulation was high (intraclass correlation coefficient=0.99,p<0.0001) and Bland-Altman agreement showed no significant difference in the estimated day of ovulation between the supervising sonographer and the panel (t=-0.28,p=0.78).Corpus luteum criteria were necessary to help identify the day of ovulation in 14/71 cycles (20%). Conclusions:The estimated day of ovulation can be reliably determined on ultrasound by trained sonographers using dominant follicle collapse and corpus luteum formation based on 6-8 scans per cycle.