Abstract: The human reproductive cycle is characterized by single follicular development. Although the controlled ovarian stimulation may promote multiple follicle development and get more oocytes，the desynchronization of follicular growth and development can not be avoided，which is caused by age，ovarian response，polycystic ovary syndrome. In order to obtain the satisfactory outcome in clinical，we should choose the appropriate protocol for each patient. The synchronization between follicles will be improved by adjusting the dosage of GnRHa，injecting HMG/GH and puncturing big ovarian follicle，etc.

Key words: Ovulation induction, Pituitary gland, Ovarian follicle, Gonadotropin-releasing hormone, Fertilization in vitro