Clinically, follicles usually ovulate at an average of 1-2cm, and under normal circumstances most follicles rupture at about 2cm, expelling an egg. Therefore, during follicle monitoring, it is recommended to have intercourse when the follicle reaches a dominant condition, such as when the follicle reaches a diameter of 18mm. After intercourse, the egg can survive for 24 hours, and the sperm can survive for 2-3 days, so that the sperm and the egg will have a chance to combine and form a fertilized egg, which will clinically achieve the purpose of pregnancy, but some people will have ovulation when the follicle diameter reaches 1cm.