This is because testing follicles is not only about checking the size of the follicles, but first of all about checking a few endometrium, which for a pregnancy requires a fertile soil, i.e. the endometrium. The thickness of the endometrium is only measured more accurately with a negative ultrasound. The other thing is the follicles and it is important to check not only the larger, dominant follicles but also how many there are. A vaginal ultrasound is recommended because especially for some infertile, polycystic ovaries, the number of follicles, their dominant follicles, and the presence of dominant follicles need to be counted. With vaginal ultrasound, the number of follicles is viewed when looking at the ovaries with polycystic ovary syndrome. If the patient is chronically infertile, it is a very effective or more helpful clinical diagnosis for polycystic ovaries by determining the number and size of follicles.