We predict that a difference of 1.2 mm between mean follicular size before and after COCPs will be clinically significant. This is based on observations by Fanchin in which women treated with luteal estradiol displayed a decrease in mean follicular size on day 3 of 1.2 mm that was associated with a significant decrease in coefficient of variation between follicles and an increase in mature follicles >16 mm number on day of hCG administration.