Can someone clear me up !

How many mm are follicles ready to release an egg? I went inn for a scan at cd 11 and i had 2 large follicles so she is having me trigger at cd 12 and <a href="https://glowing.com/glow-fertility-program">iui</a> cd 13.... now i had a almost positive opk test at cd 11 and then cd 12 it was lighter..... soo confused did i miss it??