The first thing you need to do is to see a mature follicle under the ultrasound. A mature follicle is one that is 18-23mm in diameter, and if you find an enlarged follicle under the ultrasound, it means you are ovulating. If the enlarged follicles are gone and there is a small amount of fluid in the pelvic cavity, it means that ovulation has already occurred. If the follicles continue to increase in size, you will need to go back for another ultrasound in 1 day until you find that the mature follicles are gone and there is fluid in the pelvic cavity, proving that you have ovulated. In addition, women may also find a more clear, stretched leucorrhea during ovulation, which also indicates ovulation.