There are no follicles in the uterus, it may be that the development of a gestational sac in the uterine cavity is mistaken for a follicle, which grows on the ovary. After menstruation, the follicle starts to grow in the next cycle, at a rate of about 1mm per day, and grows to about 18-24mm during ovulation before ovulation occurs. During ovulation, when there is sexual intercourse, the egg and sperm combine to form a fertilized egg, which is transplanted into the uterine cavity for 6-7 days after it is formed. With the prolongation of menopausal days, the development of a pregnancy sac in the uterine cavity during gynecological ultrasound examination at about 40 days after menopause can be diagnosed as normal intrauterine pregnancy. The growth and development of the follicle is closely related to the growth, thickening, and peeling off of the female uterine lining.