Follicle size 12 mm

Monika
I am TTC baby#1. I had my pelvic ultrasound done at CD 10 and my follicle size is 12 mm. I  am not taking any medicine. TTC naturally. Anyone have an idea if that's optimum or if it should be bigger. And at what follicle size we should BD and how much does the follicle grow in a day.
Baby dust to you all!!!