Eggs usually go to 15mm or more, we will monitor more densely, probably around 18-20mm will ovulate, of course, everyone is different, and I’m talking about most of them. It’s possible that some people may ovulate with a smaller follicle, which actually signals that this follicle may be of poor quality and her likelihood of getting pregnant will be lower; some people will ovulate beyond this size again. Usually around 18mm, the doctor will use a combination of other tests to determine if the egg is about to be ovulated, so this size is not unique, it has to be combined with her menstrual history, previous ovulation monitoring, and urine LH peaks or blood values, etc.