The follicles are measured in millimeters in 2 dimensions. When doing the u/s the focal point of the picture changes and the follicles move in and out of view. When the oval cross-section in view looks the largest, they mark it on the computer screen. The computer measures the 2 dimensions and averages them to come up with the follicle's "size". So my 5 largest follicles that measure 14 are about the size of a small marble, but a little oblong instead of round.

One of my cycle buddies has an E2 of over 3000. She's on the same day as me, and they are cutting back on her stimulation medicine for the second time. I hope she doesn't end up hyperstimulating and having her IVF cancelled. She started out on 6 amps (450iu) and is now cut back to 1 amp (75iu). It's amazing to me how differently every person responds to the medications.