Nearly all the follicles on the right ovary were measuring around 17mm. My estradiol level was 913. Ovulation is typically triggered when four or more follicles are larger than 18mm and estradiol is over 2000. Follicles typically grow about 1-2mm per day during this stage of stimulation. Choosing the exact right time is paramount. Waiting too late or going too early could create problems with egg quality which decreases fertilization rates and embryo quality.