Ovulation of a mature egg is essential for pregnancy. In a normal woman of childbearing age, about 15 to 20 small follicles begin to grow and develop each menstrual cycle, but only one follicle eventually matures and ovulates, and may be fertilized and become pregnant when it encounters sperm. During a cycle of IVF treatment, the doctor also has to stimulate a batch of follicles to a mature stage, that is, when the follicles are at least 14 to 16 mm in diameter, before a fertile and mature egg (oocyte) can be obtained. In today’s clinic, a subset of patients, especially infertile patients with polycystic ovary syndrome (PCOS), have many small immature follicles with no dominant follicle to mature. This kind of ovary responds to stimulating drugs under harsh conditions, at a certain dose, small follicles often do not respond, once the dose is increased, the many small follicles in the ovary are very sensitive to hormonal stimulation, growing together at the same time, easily causing ovarian hyperstimulation syndrome (OHSS), for this reason, for this part of the patient, the use of in vitro maturation of the oocyte (IVM) technology may provide effective help. What is in vitro oocyte maturation technique In vitro oocyte maturation technique (IVM) is an assisted reproduction technique, which simply means that immature eggs from small ovarian follicles are removed and placed in a culture solution that simulates the microenvironment of the follicle in the body for in vitro cultivation to the maturity stage, where the first polar body is discharged, and then the in vitro fertilization technique is performed to assist fertilization, which is much the same as that for the mature eggs in the body. The process of in vitro fertilization is much the same as that of mature eggs in vivo. In the 1990s, Mr. Edwards, the father of IVF, regarded in vitro maturation of oocytes (IVM) as one of the three promising technologies for the future development of assisted reproduction technology, the other two technologies being microstimulation and natural cycle IVF. Second, the development of in vitro maturation of immature eggs The world’s first case of in vitro fertilization of a mature egg was reported in 1991. Successful pregnancies and deliveries have been reported since then. The real use of clinical treatment of infertility was at the beginning of this century, mainly used in patients with PCOS, and then used in patients with different causes of infertility, including the ovary is highly responsive to a history of OHSS, the ovary is not suitable for drug stimulation and there is no mature follicle growth, the technique of removing the rest of the small follicles at the same time as the natural cycle of IVF treatment (IVF/IVM), and so on.