During egg retrieval the doctor aspirates fluid from all follicles with the visual cavity, regardless of size. It happens that some of the eggs we get from such follicles are immature but in some cases mature eggs could come from small follicles and vice versa. On ultrasound all follicles with cavity are usually seen quite clearly, so doctor wouldn't miss them. But in some rare cases the anatomy of ovaries could be quite unusual and follicles could be hard to get by transvaginal access.
Dr. Anna Gusareva
