<qa>  What is the unique feature of the WHIRL?We tracked the growth and regression of dominant follicles after administration of OC by means of highly sophisticated transvaginal ultrasonography and computerized image analysis techniques. The extremely high resolution ultrasonography of the ovarian follicles and the computer-assisted image analysis are unique to the Womens Health Imaging Research Laboratory WHIRL at the University of Saskatchewan. The synergyne R.A. Pierson image analysis program was developed in the WHIRL and has the ability to allow assessment of the physiologic status of follicles as small as 6 to 10 mm. This unique protocol will allow us to characterize patterns of follicular growth and atresia under the suppressive effects of oral contraception, as well as the assessment of anovulatory follicles which may develop when OCs are administered at advanced stages of follicular development. 