1-2-3 Rule (Ovary)

The 1-2-3 rule is a simple aide-mémoire that describes the nomenclature of any small simple anechoic structure in the ovary on ultrasound:

<1 cm = follicle

1-2 cm = dominant follicle

>3 = cyst

dominant follicle
Dominant Follicle
ovarian cyst
Simple cyst