Polycystic ovary syndrome (PCOS) cannot be diagnosed by ultrasound because polycystic ovaries are not cysts. They’re follicles or eggs which are normal for the ovary.
It’s normal for all women to sometimes have a higher number of follicles. It’s normal for young women to always have a higher number of follicles because young women have more eggs. That’s why the new international PCOS guidelines state that “ultrasound is now not recommended in diagnosis in those within 8 years of the start of periods.”